Dielectric Ceramic Composition

1. (Field of the Invention)

The present invention relates to a dielectric ceramic composition. More specifically, the invention relates to a dielectric ceramic composition which contains BaTiO.sub.3 as a chief component, as well as Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and MnO, and which can be preferably used as a material of ceramic capacitors and resonators.

2. (Description of the Related Art)

Dielectric ceramic compositions have heretofore been used as materials for multi-layer ceramic capacitors. Such a multi-layer ceramic capacitor is fabricated by stacking plural pieces of a green sheet of a dielectric ceramic composition having an internal electrode formed therein such that a predetermined capacitance is obtained followed by firing as a unitary structure. For instance, a dielectric ceramic composition used for a multi-layer ceramic capacitor of X7R (EIA Standards: change of capacitance is within .+-.15% over a temperature range of from -55.degree. C. to +125.degree. C.) has a dielectric constant of as high as not smaller than 2500 at +25.degree. C., and has a thickness of not larger than 15 .mu.m per a piece of green sheet. It is important here that the firing temperature is not higher than, for example, 1300.degree. C.

That is, by employing a green sheet having a dielectric constant of not smaller than 2500 at 25.degree. C. and a thickness of not larger than 15 .mu.m, it is allowed to minimize the thickness of the raw green between the internal electrodes and to minimize the opposing areas and, hence, to realize a multi-layer ceramic capacitor in a small size. By selecting the firing temperature to be not higher than 1300.degree. C., furthermore, it is allowed to choose the internal electrodes from an increased variety of materials such as from an expensive material consisting of 100% of palladium through up to cheap Pd-Ag. In addition to the above, sufficient degree of attention must be given to properties of the dielectric ceramic composition such as dielectric loss tan .delta. and insulation resistance, and it is further desired that the dielectric loss is little dependent upon the AC voltage.

So far, dielectric ceramic compositions containing BaTiO.sub.3, Nb.sub.2 O.sub.5 and ZnO have been proposed already featuring improved dielectric constants (see Japanese Laid-Open Patent Publications Nos. 18162/1984, 18159/1984, etc.). Dielectric constants of from 2000 to 3000 can be obtained by using such dielectric ceramic compositions. Despite of their high dielectric constants, however, such dielectric ceramic compositions have large dielectric losses tan .delta. making it difficult to decrease the thickness of the green sheet. When used for the multi-layer capacitors, therefore, a large capacitance is not obtained.

In order to decrease the dielectric loss tan .delta., a dielectric ceramic composition containing BaTiO.sub.3, Nb.sub.2 O.sub.5, MgO and La.sub.2 O.sub.3 has been developed already (see Japanese Patent Publication No. 10766/1993). There has further been proposed a composition comprising BaTiO.sub.3 to which are added Nb.sub.2 O.sub.5 and MgO in such amounts that the molar ratio of Nb.sub.2 O.sub.5 /MgO is from 2.3 to 4 as well as rare earth oxides in amounts of from 0.1 to 0.5% by weight (see Japanese Patent Publication No. 19007/1980).

In fact, however, the above-mentioned dielectric ceramics all have dielectric constants of not larger than 2200, with which it is difficult to obtain a capacitor having a large capacitance in a small size. Besides, these dielectric ceramics still have such large dielectric losses that it is difficult to decrease the thickness of the green sheet.

Moreover, the above-mentioned dielectric ceramics all have AC voltage dependence of dielectric loss of not smaller than 3.0% under the application of a voltage of 2000 V/cm, making it difficult to decrease the thickness of the dielectric layer and, hence, making it difficult to obtain a capacitor having a large capacitance in a small size.

In view of the above-mentioned problems, the present inventors have conducted keen study and have accomplished the present invention after having discovered the fact that a ceramic composition containing barium titanate (BaTiO.sub.3) as a chief component as well as Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and MnO at a predetermined composition ratio, the molar ratio of MgO to Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 lying within a particular range, exhibits a dielectric constant of as large as not smaller than 2500, has a temperature chararistics of capacitance that satisfies X7R of the EIA Standards, has a dielectric loss of as small as 2.5% or less, and has an AC voltage dependence of as small as 3.0% or less even under the application of an AC voltage of 2000 V/cm.

It is therefore an object of the present invention to provide a dielectric ceramic composition having a dielectric constant of not smaller than 2500, a temperature chararistics of capacitance satisfying X7R of the EIA Standards, a dielectric loss of as small as 2.5% or less, and such a small AC voltage dependence that the dielectric loss is not larger than 3.0% even under the application of an AC voltage of 2000 V/cm.

Another object of the present invention is to provide a dielectric ceramic composition which is obtained in the form of a layer of a decreased thickness, and is suited as a material for producing a multi-layer ceramic capacitor of a small size having a large capacitance.

A further object of the present invention is to provide a dielectric ceramic composition that can be fired at a temperature of not higher than 1300.degree. C. and can be easily produced industrially.

According to the present invention, there is provided a dielectric ceramic composition containing, per 100 parts by weight of BaTiO.sub.3, at least either one of Nb.sub.2 O.sub.5 or Ta.sub.2 O.sub.5 in an amount of from 0.8 to 3.5 parts by weight, MgO in an amount of from 0.06 to 0.7 parts by weight, oxides of rare earth elements in an amount of from 0.005 to 0.520 parts by weight, and MnO in an amount of from 0.01 to 0.30 parts by weight in the form of MnCO.sub.3, the molar ratio of MgO to Nb.sub.2 O.sub.5 or Ta.sub.2 O.sub.5 being from 0.5 to 2.2.

According to the present invention, furthermore, there is provided a dielectric ceramic composition which comprises the above-mentioned composition and further containing at least either one of SiO.sub.2 or Al.sub.2 O.sub.3 in an amount of from 0.05 to 0.50 parts by weight per 100 parts by weight of BaTiO.sub.3.

According to the present invention, there is further provided a dielectric ceramic composition which comprises the above-mentioned composition and further containing ZnO in an amount of not larger than 0.5 parts by weight per 100 parts by weight of BaTiO.sub.3.

A dielectric ceramic composition of the present invention contains BaTiO.sub.3 as a chief component as well as Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and MnO in predetermined amounts. Here, in the composition of the present invention, Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 are contained in amounts over a range of from 0.8 to 3.5 parts by weight per 100 parts by weight of BaTiO.sub.3.

When the contents of the above components are smaller than 0.8 parts by weight, the ceramic composition exhibits large dielectric loss, poor temperature characteristics and poor sintering property. When the contents of the above components exceed 3.5 parts by weight, the dielectric constant decreases and the temperature characteristics are greatly deteriorated.

It is desired that Nb.sub.2 O.sub.5 is contained in an amount within a range of from 1.3 to 3.0 parts by weight per 100 parts by weight of BaTiO.sub.3.

MgO is contained in an amount within a range of from 0.06 to 0.7 parts by weight per 100 parts by weight of BaTiO.sub.3. When the content of this component is smaller than 0.06 parts by weight, the dielectric constant and insulation resistance decrease, the temperature characteristics are deteriorated, and the voltage dependence of dielectric loss increases. When the content of this component exceeds 0.70 parts by weight, the dielectric constant drops and the insulation resistance decreases, either. It is desired that the amount of MgO lies within a range of from 0.1 to 0.4 parts by weight.

According to the present invention, the oxides of rare earth elements are contained in amounts of from 0.005 to 0.520 parts by weight. Examples of the oxides of rare earth elements used in the present invention include those oxides of, for example, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Among them, La.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Sm.sub.2 O.sub.3, Gd.sub.2 O.sub.3, and Tb.sub.4 O.sub.7 are desirably used.

When the contents of the oxides of rare earth elements are smaller than 0.005 parts by weight, the dielectric constant drops and the sintering property is deteriorated. When their contents exceed 0.520 parts by weight, the temperature characteristics are deteriorated. It is desired that the oxides of rare earth elements are contained in amounts of from 0.005 to 0.2 parts by weight.

In the present invention, furthermore, MnO is contained in an amount of from 0.01 to 0.30 parts by weight in the form of MnCO.sub.3.

When the content of this component is smaller than 0.01 part by weight, the insulation resistance decreases, dielectric loss increases and sintering property is deteriorated. When the content of this component exceeds 0.30 parts by weight, the dielectric constant drops. It is desired that MnO is contained in an amount of from 0.04 to 0.10 part by weight in the form of MnCO.sub.3.

In the present invention, furthermore, it is important that the molar ratio of MgO to Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5 is over a range of from 0.5 to 2.2. When this molar ratio is smaller than 0.5, the dielectric constant drops, and the temperature characteristics and sintering property are deteriorated. When the molar ratio is larger than 2.2, on the other hand, the temperature characteristics are deteriorated and the dielectric constant drops.

More preferably, it is desired that the molar ratio lies over a range of from 0.6 to 1.4.

According to a preferred embodiment of the present invention, a dielectric ceramic composition contains 0.8 to 2.5 parts by weight of Nb.sub.2 O.sub.5, 0.06 to 0.70 parts by weight of MgO, 0.005 to 0.520 parts by weight of at least one oxide of a rare earth element selected from La.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Gd.sub.2 O.sub.3, Tb.sub.4 O.sub.7 and Sm.sub.2 O.sub.3, and 0.01 to 0.30 parts by weight of MnO reckoned as MnCO.sub.3 per 100 parts by weight of BaTiO.sub.3, the molar ratio of MgO to Nb.sub.2 O.sub.5 lying within a range of from 0.5 to 2.2.

From the standpoint of dielectric properties contemplated by the present invention, it is more desired that, in the above-mentioned composition, the content of Nb.sub.2 O.sub.5 lies within a range of from 1.3 to 2.0 parts by weight, the content of MgO lies within a range of from 0.1 to 0.4 parts by weight, the contents of the oxides of rare earth elements lie within a range of from 0.005 to 0.2 parts by weight, and the content of MnO lies within a range of from 0.04 to 0.10 reckoned as MnCO.sub.3, the above-mentioned molar ratio lying within a range of from 0.6 to 1.4.

According to a second preferred embodiment of the present invention, the dielectric ceramic composition contains 1.3 to 3.5 parts by weight of Ta.sub.2 O.sub.5, 0.06 to 0.6 parts by weight of MgO, 0.005 to 0.5 parts by weight of oxides of rare earth elements, and 0.01 to 0.30 parts by weight of MnO reckoned as MnCO.sub.3 per 100 parts by weight of BaTiO.sub.3, the molar ratio of MgO to Ta.sub.2 O.sub.5 lying within a range of from 0.5 to 2.0.

In the composition of the second embodiment, it is more desired that the content of Ta.sub.2 O.sub.5 is from 2.0 to 3.0 parts by weight, the content of MgO is from 0.1 to 0.4 parts by weight, the contents of the oxides of rare earth elements are from 0.005 to 0.2 parts by weight, and the content of MnO is from 0.04 to 0.10 part by weight reckoned as MnCO.sub.3.

Moreover, it is desired that the molar ratio of MgO to Ta.sub.2 O.sub.5 is within a range of from 0.6 to 1.4.

It is further desired that the dielectric ceramic composition of either embodiment of the present invention containing BaTiO.sub.3, Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and MnO which are the essential components, further contains at least either one of SiO.sub.2 or Al.sub.2 O.sub.3 in an amount of from 0.05 to 0.50 parts by weight per 100 parts by weight of BaTiO.sub.3 from the standpoint of further increasing capacitance and dielectric constant, and lowering the firing temperature depending upon the composition. The above-mentioned action is not so much exhibited when the content of SiO.sub.2 or Al.sub.2 O.sub.3 is not greater than 0.05 parts by weight. When the content of SiO.sub.2 or Al.sub.2 O.sub.3 is larger than 0.50 parts by weight, on the other hand, the dielectric constant drops. More desirably, at least either SiO.sub.2 or Al.sub.2 O.sub.3 is contained in an amount of from 0.1 to 0.2 parts by weight per 100 parts by weight of BaTiO.sub.3.

According to the present invention, it is further desired that the dielectric ceramic composition comprising the essential components such as BaTiO.sub.3, etc. further contains ZnO alone or in addition to the above-mentioned SiO.sub.2 or Al.sub.2 O.sub.3 in an amount of not larger than 0.5 parts by weight and, particularly, from 0.0001 to 0.3 parts by weight per 100 parts by weight of BaTiO.sub.3, in order to further improve insulation resistance, dielectric loss, sintering property, dielectric constant and temperature characteristics of the ceramic composition. When the content of ZnO is larger than 0.5 parts by weight, the temperature characteristics are rather deteriorated and the dielectric loss increases, which are not desirable.

In the dielectric ceramic composition that contains ZnO, it is particularly desired that ZnO is contained in an amount over a range of from 0.1 to 0.5 parts by weight per 100 parts by weight of BaTiO.sub.3, and the molar ratio of the total amount of MgO and ZnO to Nb.sub.2 O.sub.5 or Ta.sub.2 O.sub.5 is from 0.5 to 2.2 from the standpoint of dielectric constant and temperature characteristics.

According to the present invention, BaTiO.sub.3 particles used for preparing the dielectric ceramic composition are those having an average particle diameter of not larger than 1.0 .mu.m and formed by, for example, calcination synthesizing method, sol-gel method, oxalic acid method or hydrothermal synthesizing method.

The dielectric ceramic composition of the present invention is prepared by weighing powders of Nb.sub.2 O.sub.5 and/or Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements and, as required, powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts with respect to 100 parts by weight of BaTiO.sub.3, wet-grinding the powders using a ball mill or the like for 20 to 48 hours followed by drying, adding a binder in a predetermined amount thereto to mold the mixture into a predetermined shape, and firing the molded article in an open air at 1200.degree. to 1300.degree. C. for 1 to 2 hours.

To obtain a multi-layer ceramic capacitor, a slurry of the above-mentioned powders is prepared and is formed into a sheet relying upon a doctor blade method, and a suitable internal electrode such as of Ag-Pd is applied onto the sheet. The sheets are then stacked in a plural number one upon the other and are fired under the above-mentioned firing conditions.

Instead of the powders of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, MgO, oxides of rare earth elements, MnCO.sub.3, SiO.sub.2, Al.sub.2 O.sub.3 and ZnO that are used in the present invention, there can be used hydroxides, carbonates, nitrates, oxalates or alkoxides of Nb, Ta, Mg, rare earth metal elements, Mn, Si, Al and Zn, that decompose at a temperature lower than the sintering temperature to form oxides.

In order to improve AC voltage dependence of the dielectric ceramic composition of the present invention, it is desired to control the average particle diameter d of the sintered product to be d<1.0 .mu.m. To control the average particle diameter d of the sintered product to be d<1.0 .mu.m, it is necessary to use a powder of barium titanate having an average particle diameter of not larger than 1.0 .mu.m as a starting material, or to decrease the particle diameter of the powder to be not larger than 0.8 .mu.m through wet-type milling executed for a long period of time, and to set the firing temperature to be as low as possible and to execute the firing for only a short period of time.

The dielectric ceramic composition of the present invention exhibits a temperature characteristics of capacitance of within .+-.15% over a range of from -55.degree. C. to 125.degree. C., a dielectric constant at +25.degree. C. of not smaller than 2500, a dielectric loss of as small as 2.5% or less despite a green sheet thereof has a thickness of 15 .mu.m, and a dielectric loss of as small as 3% or less under the application of an AC voltage of 2000 V/cm. It is therefore allowed to obtain a multi-layer capacitor which is small in size but having a large capacitance. Moreover, since the firing temperature is not higher than 1300.degree. C., the dielectric ceramic composition can be easily produced industrially permitting an internal electrode composed of cheaply available silver-palladium (Ag/Pd=20/80 to 40/60) to be incorporated therein, lending the composition itself to be well suited for producing multi-layer capacitors. Furthermore, there is obtained a dielectric ceramic composition having a dielectric loss of not larger than 2.5% and an insulation resistance (IR) of not smaller than 10.sup.4 M.OMEGA. which are sufficiently satisfactory fundamental properties.

Examples of the present invention will now be described in detail.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the hydrothermal synthesizing method was used as a chief component. Powders of Nb.sub.2 O.sub.5 MgO, La.sub.2 O.sub.3 and MnCO.sub.3 were weighed as shown in Table 1 with respect to 100 parts by Weight of BaTiO.sub.3, and were wetgrinded in a ball mill for 20 to 48 hours. Then, an organic binder agent was added thereto followed by milling, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm, overlapped in a number of 20 pieces one upon the other and was hot-pressed at 80.degree. C. to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1250.degree. to 1320.degree. C. for two hours. Then, the electrodes of the silver paste were glazed on both end surfaces at 800.degree. C. for 10 minutes to obtain samples for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute.

The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of more than 500 were measured and calculated by the line intercept method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 2.

The dielectric ceramic compositions lying within the scope of the present invention all have dielectric constants which are as large as 2500 or more and satisfy X7R characteristics (change of the capacitance is within .+-.15% over a temperature range of from -55.degree. C. to +125.degree. C.) stipulated under the EIA Standards. Moreover, the compositions have dielectric losses tan .delta. which are as small as 2.5% or less and exhibit losses of not larger than 3.0% even under the application of an AC voltage of 2000 Vrms/cm. The compositions further have insulation resistances (IR) of more than 10.sup.4 M.OMEGA..

In Table 1, samples Nos. 1-1 to 1-4 are those in which Nb.sub.2 O.sub.5 was added in an amount of from 0.7 to 2.5 parts by weight to BaTiO.sub.3 that is the chief component of the dielectric ceramic compositions. In these cases, MgO, La.sub.2 O.sub.3 and MnCO.sub.3 were added in amounts of 0.2 parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.

In the sample No. 1-1 (Nb.sub.2 O.sub.5 is added in an amount of 0.7 parts by weight), the dielectric constant .epsilon.r is as good as 3500 but the dielectric loss tan .delta. becomes as large as 3.3%. Besides, the temperature characteristics become -27%. In the samples Nos. 1-2 to 1-4 (Nb.sub.2 O.sub.5 is added in an amount of from 0.8 to 2.5 parts by weight), the dielectric constants .epsilon.r are from 2700 to 3700, dielectric losses tan .delta. are not larger than 2.5%, temperature characteristics are within .+-.14%, tan .delta. are not larger than 2.8% when an AC voltage of 2000 V/cm is applied, and insulation resistances (IR) are from 3 to 9.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, the dielectric ceramic compositions have large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss.

In the samples Nos. 1-5 to 1-9, the amount of MgO to be added to BaTiO.sub.3 which is the chief component of the dielectric ceramic compositions was changed to be from 0.05 to 0.75 parts by weight. In these cases, the amounts of Nb.sub.2 O.sub.5, La.sub.2 O.sub.5 and MnCO.sub.3 were selected to be 0.8 to 2.5 parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.

In the sample No. 1-5 (MgO is contained in an amount of 0.05 parts by weight), tan .delta. becomes 4.0% when an AC voltage of 2000 V/cm is applied. In the samples Nos. 1-6 to 1-8 (MgO is added in an amount of from 0.06 to 0.70 parts by weight), the dielectric constants .epsilon.r are from 2700 to 3100, dielectric losses tan .delta. are not larger than 2.0%, temperature characteristics are within .+-.13%, tan .delta. are not larger than 2.8% when an AC voltage of 2000 V/cm is applied, and insulation resistances (IR) are from 3 to 8.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, the dielectric ceramic compositions exhibit high dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 1-9 (MgO is added in an amount of 0.75 parts by weight), the dielectric loss tan .delta. is as good as 1.7% but the dielectric constant .epsilon.r is 2100. In the present invention, therefore, the amount of MgO to be added to the barium titanate BaTiO.sub.3 is selected to be from 0.06 to 0.70 parts by weight per 100 parts by weight of the barium titanate BaTiO.sub.3.

In the samples Nos. 1-10 to 1-14, the amount of La.sub.2 O.sub.3 to be added to BaTiO.sub.3 that is the chief component of the dielectric ceramic compositions was changed to be from 0.004 to 0.53 parts by weight. In these cases, the amounts of Nb.sub.2 O.sub.5, MgO and MnCO.sub.3 were selected to be 1.8 parts by weight, 0.3 parts by weight and 0.1 part by weight, respectively.

In the sample No. 1-10 (La.sub.2 O.sub.3 is added in an amount of 0.004 parts by weight), the dielectric loss tan .delta. is 2.5% but the dielectric constant .epsilon.r is as low as 2350. In the samples Nos. 1-11 to 1-13 (La.sub.2 O.sub.3 is added in an amount of from 0.005 to 0.52 parts by weight), the dielectric constants .epsilon.r are from 2800 to 3600, dielectric losses tan .delta. are not larger than 2.0%, temperature characteristics are within .+-.11%, tan .delta. are not larger than 2.8% when an AC voltage of 2000 V/cm is applied and insulation resistances (IR) are from 3 to 7.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, there are obtained dielectric ceramic compositions having high dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 1-14 (La.sub.2 O.sub.3 is added in an amount of 0.53 parts by weight), the dielectric constant .epsilon.r is as large as 3800 and the dielectric loss tan .delta. is as small as 1.8%, but the temperature characteristics are deteriorated. According to the present invention, therefore, the amount of La.sub.2 O.sub.3 to be added to the barium titanate BaTiO.sub.3 is selected to be from 0.005 to 0.52 parts by weight per 100 parts by weight of the barium titanate BaTiO.sub.3.

In the samples Nos. 1-15 to 1-19, the amount of MnCO.sub.3 to be added to BaTiO.sub.3 which is the chief component of the dielectric ceramic compositions was changed to be from 0.005 to 0.31 parts by weight. In these cases, the amounts of Nb.sub.2 O.sub.5 MgO and La.sub.2 O.sub.3 were selected to be 1.8 parts by weight, 0.3 parts by weight and 0.2 parts by weight.

In the sample No. 1-15 (MnCO.sub.3 is added in an amount of 0.005 parts by weight), the dielectric constant .epsilon.r is 3000 but the dielectric loss tan .delta. becomes 2.6%. Moreover, the insulation resistance is 9.times.10.sup.3 M.OMEGA.. In the samples Nos. 1-16 to 1-18 (MnCO.sub.3 is added in an amount of from 0.01 to 0.3 parts by weight), the dielectric constants .epsilon.r are from 2800 to 3000, dielectric losses tan .delta. are not larger than 2.2%, temperature characteristics are within .+-.6%, tan .delta. are not larger than 3.0% when an AC voltage of 2000 V/cm is applied and insulation resistances (IR) are from 9.times.10.sup.4 to 2.times.10.sup.5 M.OMEGA., which are within favorable ranges. That is, there are obtained dielectric ceramic compositions having large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 1-19 (MnCO.sub.3 is added in an amount of 0.31 parts by weight), the dielectric loss tan .delta. is as small as 1.4% but the dielectric constant .epsilon.r is as low as 2100. In the present invention, therefore, the amount of MnCO.sub.3 to be added to the barium titanate BaTiO.sub.3 is selected to be from 0.01 to 0.3 parts by weight per 100 parts by weight of the barium titanate BaTiO.sub.3.

To the composition of the sample No. 1-12 of Table 1 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 3. The mixture was then formed into a tape in the same manner as in Example 1. The tapes were stacked one upon the other and internal electrodes were formed to fabricate a laminate. Properties were measured in the same manner as in Example 1. The results were as shown in Table 4.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of La.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 3 and 4 that with SiO.sub.2, Al.sub.2 O.sub.3 and ZnO being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 1-12 of Table 1) and exhibit increased dielectric constants.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the oxalic acid method was used as a chief component. Powders of Nb.sub.2 O.sub.5, MgO, Nd.sub.2 O.sub.3 and MnCO.sub.3 were weighed as shown in Table 5 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1240.degree. to 1340.degree. C. for two hours. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain samples for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change capacitance depending upon the temperature was measured over a range of from -55.degree. to +125 .degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered ceramic, the surface of the ceramic was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of not smaller than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 6.

The dielectric ceramic compositions lying within the scope of the present invention all have dielectric constants which are as large as 2500 or more and satisfy X7R characteristics (change in the capacitance is within .+-.15% over a temperature range of from -55.degree. C. to +125.degree. C.) stipulated under the EIA Standards. Moreover, the dielectric ceramic compositions have dielectric losses tan .delta. which are as small as 2.5% or less and exhibit losses of not larger than 3.0% even under the application of an AC voltage of 2000 Vrms/cm. The compositions further have insulation resistances (IR) of not smaller than 10.sup.4 M.OMEGA..

In Table 5, samples Nos. 3-1 to 3-4 are those in which Nb.sub.2 O.sub.5 was added in an amount of from 0.6 to 2.5 parts by weight to BaTiO.sub.3 that is the chief component of the dielectric ceramic compositions. In these cases, MgO, Nd.sub.2 O.sub.3 and MnCO.sub.3 were added in amounts of 0.2 parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.

In the sample No. 3-1 (Nb.sub.2 O.sub.5 is added in an amount of 0.6 parts by weight), the dielectric constant .epsilon.r is as good as 3330 but the dielectric loss tan .delta. becomes as large as 3.2%. Besides, the temperature characteristics become -26%. In the samples Nos. 3-2 to 3-4 (Nb.sub.2 O.sub.5 is added in an amount of from 0.8 to 2.5 parts by weight, the dielectric constants .epsilon.r are from 2570 to 3500, dielectric losses tan .delta. are not larger than 2.5%, temperature characteristics are within .+-.14%, tan .delta. are not larger than 3.0% when an AC voltage of 2000 V/cm is applied, and insulation resistances (IR) are from 5 to 9.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, the dielectric ceramic compositions have large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss.

In the samples Nos. 3-5 to 3-9, the amount of MgO to be added to BaTiO.sub.3 which is the chief component of the dielectric ceramic compositions was changed to be from 0.04 to 0.75 parts by weight. In these cases, the amounts of Nb.sub.2 O.sub.5, Nd.sub.2 O.sub.3 and MnCO.sub.3 were selected to be 0.8 to 2.5 parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.

In the sample No. 3-5 (MgO is contained in an amount of 0.04 parts by weight), tan .delta. becomes 4.0% when an AC voltage of 2000 V/cm is applied. In the samples Nos. 3-6 to 3-8 (MgO is added in an amount of from 0.06 to 0.70 parts by weight), the dielectric constants .epsilon.r are from 2580 to 2950, dielectric losses tan .delta. are not larger than 2.0%, temperature characteristics are within .+-.13%, tan .delta. are not larger than 2.6% when an AC voltage of 2000 V/cm is applied, and insulation resistances (IR) are from 3 to 8.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, the dielectric ceramic compositions exhibit large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 3-9 (MgO is added in an amount of 0.75 parts by weight), the dielectric loss tan .delta. is as good as 1.7% but the dielectric constant .epsilon.r is 2100. In the present invention, therefore, the amount of MgO to be added to the barium titanate BaTiO.sub.3 is selected to be from 0.06 to 0.70 parts by weight per 100 parts by weight of the barium titanate BaTiO.sub.3.

In the samples Nos. 3-10 to 3-14, the amount of Nd.sub.2 O.sub.3 to be added to BaTiO.sub.3 that is the chief component of the dielectric ceramic compositions was changed from 0 to 0.55 parts by weight. In these cases, the amounts of Nb.sub.2 O.sub.5, MgO and MnCO.sub.3 were selected to be 1.8 parts by weight, 0.3 parts by weight and 0.1 part by weight, respectively.

In the sample No. 3-10 (addition of Nd.sub.2 O.sub.3 is 0), the dielectric loss tan .delta. is 2.5% but the dielectric constant .epsilon.r is as low as 2350. In the samples Nos. 3-11 to 3-13 (Nd.sub.2 O.sub.3 is added in amounts of from 0.005 to 0.52 parts by weight), the dielectric constants .epsilon.r are from 2660 to 3420, dielectric losses tan .delta. are not larger than 2.0%, temperature characteristics are within .+-.11%, tan .delta. are not larger than 2.8% when an AC voltage of 2000 V/cm is applied and insulation resistances (IR) are from 3 to 7.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, there are obtained dielectric ceramic compositions having high dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 3-14 (Nd.sub.2 O.sub.3 is added in an amount of 0.55 parts by weight), the dielectric constant .epsilon.r is as large as 3630 and the dielectric loss tan .delta. is as small as 1.8%, but the temperature characteristics are deteriorated. According to the present invention, therefore, the amount of Nd.sub.2 O.sub.3 to be added to the barium titanate BaTiO.sub.3 is selected to be from 0.005 to 0.52 parts by weight per 100 parts by weight of the barium titanate BaTiO.sub.3.

In the samples Nos. 3-15 to 3-19, the amount of MnCO.sub.3 to be added to BaTiO.sub.3 which is the chief component of the dielectric ceramic compositions was changed from 0.005 to 0.35 parts by weight.

In these cases, the amounts of Nb.sub.2 O.sub.5 MgO and Nd.sub.2 O.sub.3 were selected to be 1.8 parts by weight, 0.3 parts by weight and 0.2 parts by weight.

In the sample No. 3-15 (MnCO.sub.3 is added in an amount of 0.005 parts by weight), the dielectric constant .epsilon.r is 2850 but the dielectric loss tan .delta. becomes 2.6%. Moreover, the insulation resistance is 9.times.10.sup.3 M.OMEGA.. In the samples Nos. 3-16 to 3-18 (MnCO.sub.3 is added in an amount of from 0.01 to 0.3 parts by weight), the dielectric constants .epsilon.r are from 2650 to 2860, dielectric losses tan .delta. are not larger than 2.2%, temperature characteristics are within .+-.6%, tan .delta. are not larger than 3.0% when an AC voltage of 2000 V/cm is applied and insulation resistances (IR) are from 3.times.10.sup.4 to 1.times.10.sup.5 M.OMEGA., which are within favorable ranges. That is, there are obtained dielectric ceramic compositions having large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 3-19 (MnCO.sub.3 is added in an amount of 0.35 parts by weight), the dielectric loss tan .delta. is as small as 1.4% but the dielectric constant .epsilon.r is as low as 2200. In the present invention, therefore, the amount of MnCO.sub.3 to be added to the barium titanate BaTiO.sub.3 is selected to be from 0.01 to 0.3 parts by weight per 100 parts by weight of the barium titanate BaTiO.sub.3.

In the samples Nos. 3-20 to 3-28, the ratio of MgO to Nb.sub.2 O.sub.5 was changed to be from 0.4 to 2.2. When the ratio is as small as 0.4 or is as large as 2.3, the dielectric constants are 2310 and 2030 which are smaller than 2500. Temperature characteristics lie outside the range of the present invention, either. When the ratio is from 0.5 to 2.2, on the other hand, the dielectric constants are not smaller than 2500, and temperature characteristics and other properties become satisfactory.

To the composition of the sample No. 3-12 of Table 5 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 7. The mixture was then formed into a tape in the same manner as in Example 3. The tapes were laminated one upon the other and internal electrodes were formed to fabricate a laminate. Properties were measured in the same manner as in Example 3. The results were as shown in Table 8.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Nd.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 7 and 8 that with SiO.sub.2, Al.sub.2 O.sub.3 and ZnO being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 3-12 of Table 5) and exhibit increased dielectric constants.

Laminates were prepared in the same manner as in Example 3 but using Pr.sub.6 O.sub.11 instead of Nd.sub.2 O.sub.3, and samples for measurement were obtained in the same manner as in Example 3 but effecting the firing in the air at 1230.degree. to 1330.degree. C. for two hours. The tested results of these samples were as shown in Tables 9 and 10.

The dielectric ceramic compositions lying within the scope of the present invention all have dielectric constants which are as large as 2500 or more and satisfy X7R characteristics (change in the capacitance is within .+-.15% over a temperature range of from -55.degree. C. to +125.degree. C.) stipulated under the EIA Standards. Moreover, the dielectric ceramic compositions have dielectric losses tan .delta. which are as small as 2.5% or less and exhibit losses of not larger than 3.0% even under the application of an AC voltage of 2000 Vrms/cm. The compositions further have insulation resistances (IR) of not smaller than 10.sup.4 M.OMEGA..

To the composition of the sample No. 5-12 of Table 9 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 11, and the mixture was formed into a tape. The tape was laminated, an internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 5. The results were as shown in Table 12.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Pr.sub.6 O.sub.11, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 11 and 12 that with SiO.sub.2, Al.sub.2 O.sub.3 and ZnO being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 5-12) and exhibit increased dielectric constants.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the oxalic acid method was used as a chief component. Powders of Nb.sub.2 O.sub.5, MgO, Gd.sub.2 O.sub.3 and MnCO.sub.3 were weighed as shown in Table 13 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1240.degree. to 1320.degree. C. for two hours. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain samples for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of not smaller than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 14.

To the composition of the sample No. 7-12 of Table 13 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 15, and the mixture was formed into a tape in the same manner as in Example 7. The tape was laminated, internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 7. The results were as shown in Table 16.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Gd.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the hydrothermal synthesizing method was used as a chief component. Powders of Nb.sub.2 O.sub.5, MgO, Tb.sub.4 O.sub.7 and MnCO.sub.3 were weighed as shown in Table 17 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1250.degree. to 1340.degree. C. for two hours as shown in Table 17. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain samples for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of not smaller than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 18.

To the composition of the sample No. 9-12 of Table 17 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 19, and the mixture was formed into a tape in the same manner as in Example 9. The tape was laminated, an internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 9. The results were as shown in Table 20.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Tb.sub.4 O.sub.7, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

Laminates were prepared in the same manner as in Example 9 but using Sm.sub.2 O.sub.3 instead of Tb.sub.4 O.sub.7, and samples for measurement were obtained in the same manner as in Example 9 but effecting the firing in the air at 1260.degree. to 1340.degree. C. for two hours. The samples and the tested results were as shown in Tables 21 and 22.

To the composition of the sample No. 11-12 of Table 21 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 23, and the mixture was formed into a tape in the same manner as in Example 11. The tape was laminated, an internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 11. The results were as shown in Table 24.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Sm.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the oxalic acid method was used as a chief component. Powders of Ta.sub.2 O.sub.5, MgO, La.sub.2 O.sub.3, MnCO.sub.3, SiO.sub.2, Al.sub.2 O.sub.3 and ZnO were weighed as shown in Table 25 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1240.degree. to 1340.degree. C. for two hours. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain samples for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of not smaller than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 26.

The dielectric ceramic compositions lying within the scope of the present invention all have dielectric constants which are as large as 2500 or more and satisfy X7R characteristics (change in the 5 capacitance is within .+-.15% over a temperature range of from -55.degree. C. to +125.degree. C.) stipulated under the EIA Standards. Moreover, the dielectric losses tan .delta. are as small as 2.5% or less and exhibit losses of not larger than 3.0% even under the application of an AC voltage of 2000 Vrms/cm. The compositions further have insulation resistances (IR) of not smaller than 10.sup.4 M.OMEGA..

In Table 25, samples Nos. 13-1 to 13-4 are those in which Ta.sub.2 O.sub.5 was added in an amount of from 1.3 to 3.6 parts by weight to BaTiO.sub.3 that is the chief component of the dielectric ceramic compositions. In these cases, MgO, La.sub.2 O.sub.3 and MnCO.sub.3 were added in amounts of 0.2 parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.

In the samples Nos. 13-1 to 13-3 (Ta.sub.2 O.sub.5 is added in amounts of from 1.3 to 3.5 parts by weight), the dielectric constants .epsilon.r are from 2640 to 3600, dielectric losses tan .delta. are not larger than 2.5%, the temperature characteristics are within .+-.13%, tan .delta. are not larger than 3.0% when an AC voltage of 2000 V/cm is applied, and insulation resistances (IR) are from 6 to 9.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, the dielectric ceramic compositions have large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 13-4 (Ta.sub.2 O.sub.5 is added in an amount of 3.6 parts by weight), the dielectric constant .epsilon.r is as small as 2260 and the temperature characteristics are deteriorated down to -18%.

In the samples Nos. 13-5 to 13-8, the amount of MgO to be added to BaTiO.sub.3 which is the chief component of the dielectric ceramic compositions was changed to be from 0.05 to 0.6 parts by weight. In these cases, the amounts of Ta.sub.2 O.sub.5, La.sub.2 O.sub.3 and MnCO.sub.3 were selected to be 1.3 to 3.5 parts by weight, 0.2 parts by weight and 0.1 part by weight, respectively.

In the sample No. 13-5 (MgO is contained in an amount of 0.05 parts by weight), tan .delta. becomes 4.0% when an AC voltage of 2000 V/cm is applied. In the samples Nos. 13-6 to 13-8 (MgO is added in an amount of from 0.06 to 0.60 parts by weight), the dielectric constants .epsilon.r are from 2630 to 3020, dielectric losses tan .delta. are not larger than 2.0%, temperature characteristics are within .+-.12%, tan .delta. are not larger than 2.6% when an AC voltage of 2000 V/cm is applied, and insulation resistances (IR) are from 5 to 8.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, the dielectric ceramic compositions exhibit high dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the present invention, the amount of MgO to be added to BaTiO.sub.3 is selected to be from 0.06 to 0.70 parts by weight per 100 parts by weight of BaTiO.sub.3.

In the samples Nos. 13-9 to 13-13, the amount of La.sub.2 O.sub.3 to be added to BaTiO.sub.3 that is the chief component of the dielectric ceramic compositions was changed to be from 0 to 0.6 parts by weight. In these cases, the amounts of Ta.sub.2 O.sub.5, MgO and MnCO.sub.3 were selected to be 2.8 parts by weight, 0.3 parts by weight and 0.1 part by weight, respectively.

In the sample No. 13-9 (no La.sub.2 O.sub.3 is added), the dielectric loss tan .delta. is 2.3% but the dielectric constant .epsilon.r is as low as 2370. In the samples Nos. 13-10 to 13-12 (La.sub.2 O.sub.3 is added in an amount of from 0.005 to 0.5 parts by weight), the dielectric constants .epsilon.r are from 2740 to 3520, dielectric losses tan .delta. are not larger than 1.9%, temperature characteristics are within .+-.10%, tan .delta. are not larger than 2.8% when an AC voltage of 2000 V/cm is applied and insulation resistances (IR) are from 5 to 7.times.10.sup.4 M.OMEGA., which are within favorable ranges. That is, there are obtained dielectric ceramic compositions having high dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 13-13 (La.sub.2 O.sub.3 is added in an amount of 0.6 parts by weight), the dielectric constant .epsilon.r is as large as 3820 and the dielectric loss tan .delta. is as small as 1.7%, but the temperature characteristics are deteriorated down to -20%. According to the present invention, therefore, the amount of La.sub.2 O.sub.3 to be added to BaTiO.sub.3 is selected to be from 0.005 to 0.520 parts by weight per 100 parts by weight of BaTiO.sub.3.

In the samples Nos. 13-14 to 13-18, the amount of MnCO.sub.3 to be added to BaTiO.sub.3 which is the chief component of the dielectric ceramic compositions was changed to be from 0.005 to 0.4 parts by weight. In these cases, the amounts of Ta.sub.2 O.sub.5 MgO and La.sub.2 O.sub.3 were selected to be 2.8 parts by weight, 0.3 parts by weight and 0.2 parts by weight. In the sample No. 13-14 (MnCO.sub.3 is added in an amount of 0.005 parts by weight), the dielectric constant .epsilon.r is 2930 but the dielectric loss tan .delta. becomes 2.6%. Moreover, the insulation resistance is 8.times.10.sup.3 M.OMEGA.. In the samples Nos. 13-15 to 13-17 (MnCO.sub.3 is added in an amount of from 0.01 to 0.3 parts by weight), the dielectric constants .epsilon.r are from 2560 to 2880, dielectric losses tan .delta. are not larger than 2.2%, temperature characteristics are within .+-.8%, tan .delta. are not larger than 2.9% when an AC voltage of 2000 V/cm is applied and insulation resistances (IR) are from 5.times.10.sup.4 to 1.times.10.sup.5 M.OMEGA., which are within favorable ranges. That is, there are obtained dielectric ceramic compositions having large dielectric constants .epsilon.r, excellent temperature characteristics, small dielectric losses tan .delta. and small AC voltage dependence of dielectric loss. In the sample No. 13-18 (MnCO.sub.3 is added in an amount of 0.4 parts by weight), the dielectric loss tan .delta. is as small as 1.5% but the dielectric constant .epsilon.r is as low as 2230. In the present invention, therefore, the amount of MnCO.sub.3 to be added to BaTiO.sub.3 is selected to be from 0.01 to 0.3 parts by weight per 100 parts by weight of BaTiO.sub.3.

In the samples Nos. 13-19 to 13-26, the molar ratio of MgO to Ta.sub.2 O.sub.5 was changed to be from 0.4 to 2.0. When the molar ratio is as small as 0.4 or is larger than 2.2, the dielectric constant becomes small and the temperature characteristics lie outside the range of the invention, either. When the molar ratio is within a range of from 0.5 to 2.2, on the other hand, the dielectric constant becomes not smaller than 2500, and the temperature characteristics and other properties become satisfactory.

To the composition of the sample No. 13-11 of Table 25 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 27. The mixture was then formed into a tape in the same manner as in Example 13. The tape was laminated one upon the other and internal electrodes were formed to fabricate a laminate. Properties were measured in the same manner as in Example 13. The results were as shown in Table 28.

The sample possessed a composition comprising 2.8 parts by weight of Ta.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of La.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 27 and 28 that with SiO.sub.2, Al.sub.2 O.sub.3 and ZnO being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 13-11) and exhibit increased dielectric constants.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the oxalic acid method was used as a chief component. Powders of Ta.sub.2 O.sub.5, MgO, Nd.sub.2 O.sub.3 and MnCO.sub.3 were weighed as shown in Table 29 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1260.degree. to 1340.degree. C. for two hours. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain a sample for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of more than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 30.

To the composition of the sample No. 15-11 of Table 29 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 31, and the mixture was formed into a tape in the same manner as in Example 15. The tape was laminated, an internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 15. The results were as shown in Table 32.

The sample possessed a composition comprising 2.8 parts by weight of Ta.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Nd.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 31 and 32 that with SiO.sub.2, Al.sub.2 O.sub.3 and ZnO being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 15-11) and exhibit increased dielectric constants.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the oxalic acid method was used as a chief component. Powders of at least one of the oxides of rare earth elements (RE oxides) such as Ta.sub.2 O.sub.5, MgO, Pr.sub.6 O.sub.11, Sm.sub.2 O.sub.3, Gd.sub.2 O.sub.3 and Tb.sub.4 O.sub.7, as well as MnCO.sub.3 were weighed as shown in Tables 33 and 34 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1240.degree. to 1340.degree. C. for two hours. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain a sample for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of more than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Tables 35 and 36.

The dielectric ceramic compositions lying within the scope of the present invention all have dielectric constants which are as large as 2500 or more and satisfy X7R characteristics (change in the capacitance is within .+-.15% over a temperature range of from -55.degree. C. to +125.degree. C.) stipulated under the EIA Standards. Moreover, the dielectric losses tan .delta. are as small as 2.5% or less and exhibit losses of not larger than 3.0% even under the application of an AC voltage of 2000 Vrms/cm. The compositions further have insulation resistances (IR) of not smaller than 10.sup.4 M.OMEGA..

To the composition of the sample No. 17-11 of Table 33 were added the powders of SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in amounts as shown in Table 37, and the mixture was formed into a tape in the same manner as in Example 13. The tape was laminated, an internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 13. The results were as shown in Table 38.

The sample possessed a composition comprising 2.8 parts by weight of Ta.sub.2 O.sub.5, 0.3 parts by weight of MgO, 0.2 parts by weight of Pr.sub.6 O.sub.11, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2, Al.sub.2 O.sub.3 and ZnO in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 37 and 38 that with SiO.sub.2, Al.sub.2 O.sub.3 and ZnO being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 17-11) and exhibit increased dielectric constants.

A BaTiO.sub.3 powder having an average particle diameter of not larger than 1.0 .mu.m formed by the hydrothermal synthesizing method was used as a chief component. Powders of Nb.sub.2 O.sub.5, MgO, La.sub.2 O.sub.3, MnCO.sub.3 and ZnO were weighed as shown in Table 39 with respect to 100 parts by weight of BaTiO.sub.3, and were wet-pulverized in a ball mill for 20 to 48 hours. Then, an organic sticking agent was added thereto followed by stirring, and the mixture was formed into a tape having a thickness of 15 .mu.m by the doctor blade method. The tape was cut into 130 mm.times.100 mm and was overlapped in a number of 20 pieces one upon the other and was hot-pressed at 80.degree. C. to prepare a laminate thereof.

An Ag paste (Ag/Pd=30/70) was printed to form an internal electrode. The laminate was cut into 3.2 mm.times.1.6 mm and was fired in the air at 1250.degree. to 1340.degree. C. for two hours. Then, the electrodes of the silver paste were printed on both end surfaces at 800.degree. C. for 10 minutes to obtain samples for measurement.

The thus obtained samples were measured for their capacitances and dielectric losses at a reference temperature of 25.degree. C., a frequency of 1.0 KHz and a voltage of 1.0 Vrms. The change of capacitance depending upon the temperature was measured over a range of from -55.degree. to +125.degree. C., and the capacitance at +25.degree. C. was used as a reference. The insulation resistance was measured at a moment after a DC voltage of 25 V was applied for one minute. The dielectric constant was calculated from the capacitance.

As for the average particle diameter of the sintered product, the surface of the sintered product was observed using a scanning-type electron microscope at a magnification of 15000 times, and particles of more than 500 were measured and calculated by the line intercepting method. Furthermore, the dielectric loss was measured by applying a voltage of 2000 Vrms/cm at a frequency of 1 KHz. The results were as shown in Table 40.

The dielectric ceramic compositions lying within the scope of the present invention all have dielectric constants which are as large as 2500 or more and satisfy X7R characteristics (change in the capacitance is within +15% over a temperature range of from -55.degree. C. to +125.degree. C.) stipulated under the EIA Standards. Moreover, the dielectric deramic compositions have dielectric losses tan .delta. which are as small as 2.5% or less and exhibit losses of not larger than 3.0% even under the application of an AC voltage of 2000 Vrms/cm. The compositions further have insulation resistances (IR) of not smaller than 10.sup.4 M.OMEGA..

To the composition of the sample No. 19-5 of Table 39 were added the powders of SiO.sub.2 and Al.sub.2 O.sub.3 in amounts as shown in Table 41, and the mixture was formed into a tape in the same manner as in Example 19. The tape was laminated, an internal electrode was formed, and a laminate was prepared. Properties were measured in the same manner as in Example 19. The results were as shown in Table 42.

The sample possessed a composition comprising 1.8 parts by weight of Nb.sub.2 O.sub.5, 0.2 parts by weight of MgO, 0.2 parts by weight of La.sub.2 O.sub.3, 0.1 part by weight of MnO reckoned as MnCO.sub.3, and SiO.sub.2 and Al.sub.2 O.sub.3 in predetermined amounts per 100 parts by weight of BaTiO.sub.3.

It will be understood from these Tables 41 and 42 that with SiO.sub.2 and Al.sub.2 O.sub.3 being contained, the compositions are fired at temperatures lower than those of when these compounds are not contained (sample No. 19-5) and exhibit increased dielectric constants.