Dielectric ceramic composition and its use in a monolithic ceramic capacitor

Abstract: The present invention provides a dielectric ceramic composition which comprises a primary component and a secondary component in a molar ratio of from 100/0.5 to 100/5.0 and an auxiliary component in an amount of from 0.2 to 3.0 parts by weight for 100 parts by weight in total of said primary and secondary components, said primary component being composed of barium titanate (containing less than 0.02 wt% of alkali metal oxide as an impurity), scandium oxide, yttrium oxide, samarium oxide, europium oxide, manganese oxide, cobalt oxide, and nickel oxide, as expressed by the compositional formula below: (1 - α - β - γ) {BaO} m ×TiO 2 + αM 2 O 3 + βRe 2 O 3 + γ(Mn 1-x-y Ni x Co y )O (where M 2 O 3 denotes Sc 2 O 3 or Y 2 O 3 or both, Re 2 O 3 denotes Sm 2 O 3 or Eu 2 O 3 or both, α, β, γ, m, x, and y are defined by: 0.0025 ≤ α + β ≤ 0.025 0 < β ≤ 0.0075 0.0025 ≤ γ ≤ 0.05 γ/(α + β) ≤ 4 0 ≤ x < 1.0 0 ≤ y < 1.0 0 ≤ x + y < 1.0 1.0000 < m ≤ 1.035 said secondary component being magnesium oxide (MgO), and said auxiliary component being an oxide represented by Li 2 O-(Si,Ti)O 2 -Al 2 O 3 -ZrO 2 . The above dielectric ceramic composition can be used for a monolithic ceramic capacitor having internal electrodes made from nickel or nickel alloy. The dielectric ceramic composition can be sintered without the possibility of becoming a semiconductor even when sintered in an atmosphere having a low oxygen partial pressure and has a permittivity higher than 3000 and also has an insulation resistance and an electrostatic capacity such that their product (CR) is greater than 6000 Ω×F.

Description: The present invention relates to a dielectric ceramic composition and use of the dielectric ceramic composition for a monolithic ceramic capacitor, especially for a monolithic ceramic capacitor provided with internal electrodes of nickel or nickel alloy. Conventional dielectric materials composed mainly of barium titanate, which are used for ceramic capacitors, pose a problem of becoming a semiconductor as the result of reduction upon firing in a neutral or reducing atmosphere having a low oxygen partial pressure. Therefore, it is necessary to make internal electrodes from precious metal (such as palladium and platinum) which does not melt at the sintering temperature of the dielectric ceramic materials during firing in an atmosphere having a high oxygen partial pressure which prevents the dielectric ceramic material from becoming a semiconductor. This is a great hindrance to the cost reduction of monolithic ceramic capacitors. One way to address the above-mentioned problem is to make internal electrodes from an inexpensive base metal such as nickel. Unfortunately, such internal electrodes become oxidized (and hence become useless) upon firing under the conventional conditions. To avoid this problem it is necessary to use a dielectric ceramic composition which does not become a semiconductor but becomes a dielectric ceramics having sufficient resistivity and good dielectric properties even when fired in a neutral or reducing atmosphere having a low oxygen partial pressure. Those materials meeting this condition have been proposed as follows: A composition based on BaTiO 3 -CaZrO 3 -MnO-MgO, as disclosed in Japanese Patent Laid-open No. 256422/1987. A composition based on BaTiO 3 -MnO-MgO-rare earth oxide, as disclosed in Japanese Patent Laid-open No. 103861/1985. A composition based on BaTiO 3 -(Mg, Zn, Sr, Ca)O-Li 2 O-SiO 2 -MO (where MO denotes BaO, SrO, or CaO), as disclosed in Japanese Patent Publication No. 14610/1986. JP-A-07 272 973 describes a ceramic dielectric composition the main component of which is barium titanate containing at least one of scandium oxide and yttrium oxide, at least one of samarium oxide and europium oxide, and a phosphate or vanadate of manganese or nickel. MgO and/or ZnO as well as CaO and/or SrO may be admixed, and Li 2 O and SiO 2 may be present as an additive. The above-mentioned first composition (which is a non-reducible dielectric ceramic composition) suffers the disadvantage that CaZrO 3 and CaTiO 2 (which form during firing) combine with Mn to cause heterogeneity. This poses a problem with decrease in reliability at high temperatures. The above-mentioned second composition (which is a non-reducible dielectric ceramic composition) suffers the disadvantage that its insulation resistance and capacity are greatly affected by the grain size of BaTiO 3 as the principal component. This causes difficulties in producing stable characteristic properties. In addition, it has an unpractically low CR value of 1000-2000 Ω×F (which is a product of insulation resistance and electrostatic capacity). The above-mentioned third composition suffers the disadvantage of giving rise to a dielectric material having a permittivity of 2000-2800, which is inferior to conventional compositions containing precious metal (such as palladium) which have a permittivity of 3000-3500. Therefore, it will not meet the requirement for capacitors having a smaller size and a large capacity if it is used to replace conventional materials only for cost reduction. In addition, the non-reducible dielectric ceramic compositions proposed so far suffer the disadvantage of greatly decreasing in resistance at high temperatures (although they have high insulation resistance at room temperature). Decrease in resistance occurs remarkably especially in a strong electric field. This is a great hindrance to the reduction of thickness of dielectric layers. This is the reason why there has been no practical thin-layer laminated capacitors made of non-reducible dielectric ceramic compositions. Moreover, as compared with the prior art technology that employs internal electrodes of precious metal (such as palladium), they are poor in reliability at high temperatures under high humidity (or so-called moisture-resistant load characteristics). In order to address the above-mentioned problems, the present inventors have proposed some new non-reducible dielectric ceramic compositions in Japanese Patent Laid-open Nos. 9066-9068/1993. Recent requirements for improved performance at high temperatures under high humidity have made it necessary to propose new compositions having better characteristic properties. It is an object of the present invention to provide a dielectric ceramic composition which can be sintered without the possibility of becoming a semiconductor even when sintered in an atmosphere having a low oxygen partial pressure and which has a permittivity higher than 3000 and also an insulation resistance and an electrostatic capacity such that their product (CR) is greater than 6000 Ω×F. It is another object of the present invention to provide a monolithic ceramic capacitor having the following features. A small rate of decrease in insulation resistance in a strong electric field. High reliability despite thin dielectric layers. High rated voltage. Temperature characteristics of electrostatic capacity meeting the B specification prescribed in JIS and X7R specification prescribed in EIA. Good load characteristics at high temperatures under high humidity. Small size and high capacity. The present invention provides a dielectric ceramic composition which comprises a primary component and a secondary component in a molar ratio of from 100/0.5 to 100/5.0 and an auxiliary component in an amount of from 0.2 to 3.0 parts by weight for 100 parts by weight in total of said primary and secondary components, said primary component being composed of barium titanate containing less than 0.02 wt% of alkali metal oxide as an impurity, at least one of scandium oxide, and yttrium oxide, at least one of samarium oxide and europium oxide and manganese oxide optionally containing cobalt oxide and/or nickel oxide, as expressed by the compositional formula below: (1 -α-β-γ) {BaO} m ×TiO 2 + αM 2 O 3 + βRe 2 O 3 + γ(Mn 1-x-y Ni x Co y )O (where M 2 O 3 denotes Sc 2 O 3 or Y 2 O 3 or both, Re 2 O 3 denotes Sm 2 O 3 or Eu 2 O 3 or both, α, β, γ, m, x, and y are defined by: 0.0025 ≤ α + β ≤ 0.025 0 < β ≤ 0.0075 0.0025 ≤ γ ≤ 0.05 γ/(α + β) ≤ 4 0 ≤ x < 1.0 0 ≤ y < 1.0 0 ≤ x + y < 1.0 1.0000 < m ≤ 1.035 said secondary component being magnesium oxide (MgO), and said auxiliary component being an oxide represented by Li 2 O-(Si,Ti)O 2 -Al 2 O 3 -ZrO 2 . The present invention further provides a dielectric ceramic composition as defined above, wherein said auxiliary component is represented by the general formula of pLi 2 O-q(Si z Ti 1-z )O 2 -rM (where p, q, and r denote the mol% of the respective constituents, z is defined by 0.30 ≤ z ≤ 1.0, M stands for Al 2 O 3 or ZrO 2 or both, and p, q, and r are within the area enclosed by the polygon having apexes defined as follows in the triangular coordinates: A (20, 80, 0) B (10, 80, 10) C (10, 70, 20) D (35, 45, 20) E (45, 45, 10) F (45, 55, 0) provided that 0.3 ≤ z < 1.0 for the composition corresponding to the line A-F. The present invention further provides a use of the above described dielectric ceramic compositions for a monolithic ceramic capacitor comprising; a plurality of dielectric ceramic layers made from said dielectric ceramic composition, a plurality of internal electrodes made from nickel or nickel alloy formed between said dielectric ceramic layers. In a preferable embodiment, the above described internal electrodes show their edges from the ends of the dielectric ceramic layers, and external electrodes are electrically connected to the edges of said internal electrodes. In the other preferable embodiment, the above described external electrodes are constructed of sintered layers of electrically conductive metal powder containing or not containing glass frit. In the other preferable embodiment, the above described sintered layers have a plated layer thereon. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram (triangular coordinates) showing the compositional variables of three components constituting the oxide glass contained in the dielectric ceramic composition. Fig. 2 is a sectional view showing the monolithic ceramic capacitor using the composition of the present invention. Example 1 Four kinds of barium titanate (BaTiO 3 ) as shown in Table 1 were prepared from TiCl 4 and Ba(NO 3 ) 2 (both varying in purity) in prescribed amounts by precipitation in the form of titanylbarium oxalate (BaTiO(C 2 O 4 )×4H 2 O) with oxalic acid, followed by pyrolysis at 1000°C or above. Designation of BaTiO 3 Content of impurities (wt%) Average grain size (µm) Alkali metal oxide SrO CaO SiO 2 Al 2 O 3 A 0.003 0.012 0.001 0.010 0.005 0.60 B 0.020 0.010 0.003 0.019 0.008 0.56 C 0.012 0.179 0.018 0.155 0.071 0.72 D 0.062 0.014 0.001 0.019 0.004 0.58 A powder was prepared from oxides, carbonates, and hydroxides of respective components for the compositional formula 0.25 Li 2 O-0.65 (0.30 TiO 2 ×0.70 SiO 2 )-0.10 Al 2 O 3 (in molar ratio) by mixing, crushing, evaporation, and drying. This powder was made into an oxide glass powder having an average grain size smaller than 1 µm by melting at 1300°C, quenching, and crushing. Each sample in powder form was prepared by mixing from barium titanate (prepared as mentioned above), BaCO 3 (to adjust the Ba/Ti molar ratio m in barium titanate), oxide glass powder (prepared as mentioned above), and Sc 2 O 3 , Y 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , MnCO 3 , NiO, Co 2 O 3 , and MgO, all of which have a purity higher than 99%, as much as necessary to conform to the compositional formula shown in Table 2. The powder mixture obtained as mentioned above was mixed with a binder (polyvinyl butyral) and an organic solvent (ethanol) by wet ball-milling to give a ceramics slurry. By using the doctor blade method, the slurry was made into a rectangular ceramics green sheet, 11 µm thick. The green sheet was coated with a nickel-based conductive paste by printing, so as to form a conductive paste layer which becomes the internal electrode afterward. Several pieces of the green sheets, each having the conductive paste layer, were placed on top of the other to give a laminate such that the conductive paste layers show themselves alternately on one side of the laminate. The resulting laminate was heated at 350°C in a nitrogen atmosphere so as to burn the binder and then fired at the firing temperature shown in Table 3 for 2 hours in a reducing gas atmosphere composed of H 2 , O 2 , and H 2 O, with the oxygen partial pressure being 10 -9 - 10 -12 MPa. Thus there was obtained a sintered body. The sintered body had its both ends coated with a silver paste, which was subsequently baked at 600°C in a nitrogen atmosphere. This step formed external electrodes (electrically connected to internal electrodes). Thus there was obtained a monolithic ceramic capacitor. The thus obtained monolithic ceramic capacitor measures 1.6 mm wide, 3.2 mm long, and 1.2 mm thick, and the dielectric ceramic layer held between the internal electrodes is 8 µm thick. The effective dielectric ceramic layers count 19, and the area of opposed electrodes for each layer is 2.1 mm 2 . The monolithic ceramic capacitor was tested for the following characteristic properties. Electrostatic capacity (C) and dielectric loss (tan δ), measured at 1 kHz and 1 V rms and 20°C with an automatic bridge-type meter. Permittivity (ε) was calculated from the electrostatic capacity. Insulation resistance (R), measured at 25°C and 125°C with an insulation resistance meter by application of DC voltages of 16V and 160V for 2 minutes. CR products at different temperatures and voltages were calculated from the electrostatic capacity (C) and insulation resistance (R). Rate of change with temperature in electrostatic capacity, expressed in terms of ΔC/C 20°C and ΔC/C 25°C the former representing the rate of change at -25°C and 85°C relative to the electrostatic capacity at 20°C, and the latter representing the rate of change at -55°C and 125°C relative to the electrostatic capacity at 25°C. Maximum rate of change (|ΔC| max ), in terms of absolute value, in the range from -55°C to 125°C. Life under load at high temperatures was tested (on 36 specimens for each test) by measuring the change with time in insulation resistance that occurred when a DC voltage of 100V was applied at 150°C. Time required for each specimen to decrease in insulation resistance (R) below 10 6 Ω is regarded as its life. The results are given in terms of average life time. Humidity resistance under load was tested (on 72 specimens for each test) by measuring the change with time in insulation resistance that occurred when a DC voltage of 16V was applied at 121°C and 2 atmospheric pressure (100% RH). The results are expressed in terms of the number of the defective specimens which decreased in insulation resistance (R) below 10 6 Ω within 250 hours. The results of the above-mentioned tests are shown in Table 3. In Tables 2 and 3, those samples not pertaining to the present invention are indicated by an asterisk. It is apparent from Tables 1 to 3 that the monolithic ceramic capacitors pertaining to the present invention have a permittivity (ε) higher than 3000, a dielectric loss tangent (tan δ) lower than 2.5%, and a rate of change with temperature in electrostatic capacity that meets the B specification prescribed in JIS in the temperature range from -25°C to 85°C and also meets the X7R specification prescribed in EIA in the temperature range from -55°C to 125°C. In addition, the samples pertaining to the present invention have a high insulation resistance measured for 16V and 160V at 25°C which is evidenced by the respective CR products of 6000 Ω×F and 2000 Ω×F. They also have a high insulation resistance measured for 16V and 160V at 125°C which is evidenced by the respective CR products of 2000 Ω×F and 500 Ω×F. They have an average life longer than 500 hours and pass the humidity load test. They can be formed by sintering at comparatively low temperatures (1300°C or below). The compositional variables specified in the present invention are based on the following experimental facts. Sample No. 1, in which the amount (α+β) of (M 2 O 3 + Re 2 O 3 ) is less than 0.0025, has a permittivity (ε) lower than 3000, a dielectric loss tangent (tan δ) higher than 2.5%, a high rate of change with time in electrostatic capacity, and an extremely short life. Sample No. 19, in which the amount (α+β) of (M 2 O 3 + Re 2 O 3 ) is more than 0.025, has a permittivity (ε) lower than 3000, a low insulation resistance, and a short average life. In addition, it needs a high sintering temperature and gives rise to some defectives in the humidity load test. Sample No. 2, in which the amount (γ) of (Mn, Ni, Co)O is less than 0.0025, is subject to reduction during firing in a reducing atmosphere. This reduction changes the ceramics into a semiconductor, thereby decreasing its insulation resistance (which is undesirable). Sample No. 20, in which the amount (γ) of (Mn, Ni, Co)O exceeds 0.05, has a low insulation resistance at 25°C (with 160V) and at 125°C and an average life shorter than 500 hours. Samples Nos. 23 to 25, which do not contain Mn at all, have a low insulation resistance and an average life shorter than 500 hours. Sample No. 3, in which the value of b is 0, has an average life shorter than 500 hours. Sample No. 22, in which the value of b exceeds 0.0075, has a high rate of change with temperature in electrostatic capacity. Hence, it does not meet the B specification of JIS and the X7R specification of EIA. Sample No. 21, in which the ratio γ/(α+β) exceeds 4, has a high rate of change with temperature in electrostatic capacity (which is not desirable). Samples Nos. 4 and 5, in which the molar ratio (m) of barium titanate is smaller than or equal to 1.000, is subject to change into semiconductor and has a low insulation resistance and an average life shorter than 500 hours. Sample No. 26, in which the molar ratio (m) exceeds 1.035, is not capable of sintering even at 1350°C. Sample No. 6, in which the amount of MgO is less than 0.5 mole, has an insulation resistance lower than 2000 Ω×F (at 25°C and 160V) and an average life shorter than 500 hours. In addition, it has a rate of change with temperature in electrostatic capacity which does not meet the B specification of JIS and the X7R specification of EIA. By contrast, Sample No. 27, in which the amount of MgO exceeds 5 moles, needs a high sintering temperature, has a permittivity lower than 3000, is poor in insulation resistance, and fails the humidity load test. Sample No. 7, in which the amount of oxide glass is less than 0.2 parts by weight, is not completely sintered even at 1350°C. By contrast, Sample No. 28, in which the amount of oxide glass exceeds 3.0 parts by weight, has a low permittivity and a high rate of change with temperature in electrostatic capacity. Sample No. 29, in which the amount of alkali metal (as an impurity in barium titanate) exceeds 0.02 parts by weight, has a low permittivity. Although the value of ratio β/α is not particularly specified, it should desirably be smaller than or equal to 1 so that the samples have a rate of change with temperature in electrostatic capacity which meets the specification with a margin. Example 2 A powder of dielectric material was prepared from barium titanate (designated as A in Table 1) and respective starting materials in such amounts as specified below. 97.3 {BaO} 1.010 ×TiO 2 + 0.6 Y 2 O 3 + 0.1 Sm 2 O 3 + 0.6 MnO + 0.6 NiO + 0.8 CoO (in molar ratio). This powder was incorporated with 1.2 moles of MgO. The thus prepared raw material was incorporated with an oxide glass (having an average particle size smaller than 1 µm) as shown in Table 4). This oxide glass was prepared in the same manner as in Example 1. The resulting dielectric ceramic composition was made into monolithic ceramic capacitors in the same manner as in Example 1. (The monolithic ceramic capacitor has internal electrodes and silver external electrodes electrically connected to the internal electrodes.) Incidentally, the glass melting temperature was adjusted in the range of 1200-1500°C according to the glass composition. Sample No. Amount of glass (wt%) Components of oxide glass (wt%) Li 2 O Si z Ti 1-z z Al 2 O 3 ZrO 3 1 1.00 20 80 0.3 0 0 2 0.80 10 80 0.6 5 5 3 1.00 10 70 0.5 20 0 4 1.00 35 45 1.0 10 10 5 1.20 45 45 0.5 10 0 6 1.00 45 55 0.3 0 0 7 0.80 20 70 0.6 5 5 8 1.00 20 70 0.4 10 0 9 1.00 30 60 0.7 5 5 10 0.80 30 60 0.8 10 0 11 1.50 40 50 0.6 5 5 12 2.00 40 50 0.9 0 10 13* 1.20 10 85 0.4 5 0 14* 1.50 5 75 0.6 10 10 15* 1.00 20 55 0.5 25 0 16* 1.20 45 40 0.8 0 15 17* 1.00 50 45 0.7 5 0 18 0.80 25 75 0.9 0 0 19* 1.00 25 75 1.0 0 0 20 1.50 35 65 0.9 0 0 21* 1.20 35 65 1.0 0 0 22* 1.00 20 70 0.2 0 10 The composition of the oxide glass is defined by the triangular coordinates shown in Fig. 1. The monolithic ceramic capacitors in this example have the same dimensions as those in Example 1. The monolithic ceramic capacitors were tested for electrical properties as follows: Electrostatic capacity (C) and dielectric loss (tan δ), measured at 1 kHz and 1 V rms and 20°C with an automatic bridge-type meter. Permittivity (ε) was calculated from the electrostatic capacity. Insulation resistance (R), measured at 25°C and 125°C with an insulation resistance meter by application of ΔC voltages of 16V and 160V for 2 minutes. CR products at different temperatures and voltages were calculated from the electrostatic capacity (C) and insulation resistance (R). Rate of change with temperature in electrostatic capacity, expressed in terms of ΔC/C 20°C and ΔC/C 25°C the former representing the rate of change at -25°C and 85°C relative to the electrostatic capacity at 20°C, and the latter representing the rate of change at -55°C and 125°C relative to the electrostatic capacity at 25°C. Maximum rate of change (|ΔC| max ), in terms of absolute value, in the range from -55°C to 125°C. Life under load at high temperatures was tested (on 36 specimens for each test) by measuring the change with time in insulation resistance that occurred when a DC voltage of 100V was applied at 150°C. Time required for each specimen to decrease in insulation resistance (R) below 10 6 Ω is regarded as its life. The results are given in terms of average life time. Humidity resistance under load was tested (on 72 specimens for each test) by measuring the change with time in insulation resistance that occurred when a DC voltage of 16V was applied at 121°C and 2 atmospheric pressure (100% RH). The results are expressed in terms of the number of the defective specimens which decreased in insulation resistance (R) below 10 6 Ω within 250 hours. The results of the above-mentioned tests are shown in Table 5. In Tables 4 and 5, those samples not pertaining to the present invention of claim 2 are indicated by an asterisk. It is apparent from Tables 4 and 5 that the monolithic ceramic capacitors composed of dielectric ceramic layers containing the oxide glass specified in the present invention have a permittivity (ε) higher than 3000, a dielectric loss tangent (tan δ) lower than 2.5%, and a rate of change with temperature in electrostatic capacity that meets the X7R specification prescribed in EIA in the temperature range from -55°C to 125°C. In addition, the samples pertaining to the present invention have a high insulation resistance measured for 16V and 160V at 25°C which is evidenced by the respective CR products of 6000 Ω×F and 2000 Ω×F. They also have a high insulation resistance measured for 16V and 160V at 125°C which is evidenced by the respective CR products of 2000 Ω×F and 500 Ω×F. They have an average life longer than 500 hours and pass the humidity load test. They can be formed by sintering at comparatively low temperatures (1300°C or below). The composition of the oxide glass is specified by the area enclosed by six lines in the triangular coordinates as mentioned above. This is justified by the fact that Samples Nos. 13 to 17 are poor in sinterability and liable to fail the humidity load test. However, the composition corresponding to the line A-F (with z = 1.0) is excluded from the scope of the invention. This is justified by the fact that Sample No. 19 has a high sintering temperature and fails the humidity load test. The composition having the value of z smaller than 0.3 is also excluded from the scope of the invention. This is justified by the fact that Sample No. 22 has a high sintering temperature and fails the humidity load test. Fig. 2 is a sectional view showing the monolithic ceramic capacitor pertaining to the present invention. The monolithic ceramic capacitor 1 is composed of dielectric ceramic layers 3 and internal electrodes 2a, 2b, 2c, and 2d, which are placed alternately on top of the other. The monolithic ceramic capacitor 1 has external electrodes 4a and 4b which are electrically connected to the internal electrodes 2a, 2b, 2c, and 2d. The external electrodes 4a and 4b have another external electrodes 5a and 5b of nickel or copper formed thereon by plating. The external electrodes 5a and 5b have another external electrodes 6a and 6b of solder or tin formed thereon by plating. The monolithic ceramic capacitor 1 can be obtained by the manufacturing process mentioned in Example 1 or 2. The one shown in Fig. 2 has the external electrodes of three-layer structure; however, the external electrodes may be of single-layer structure or multi-layer structure depending on the usage of the capacitor. Although barium titanate in powder form prepared from the oxalic acid method was used in the above-mentioned examples, it may be replaced by the one prepared by the alkoxide method or hydrothermal method so as to improve the characteristic properties of the monolithic ceramic capacitor. In addition, yttrium, cobalt, and nickel may be used in the form of alkoxide solution or organometal solution in place of oxide powder without any adverse effect of the characteristic properties so long as they are used in specified amounts for the dielectric ceramic composition. The internal electrodes may be formed by any of screen printing, vacuum deposition, and plating. The external electrodes may be formed from the same material as used for the internal electrodes. It may also be formed from silver, palladium, or silver-palladium alloy, which may be adequately selected depending on the usage of the monolithic ceramic capacitor. In the examples mentioned above, the external electrodes were formed by coating with metal powder paste and subsequent baking after firing. Alternatively, they may be formed by coating prior to firing and subsequent baking simultaneous with the firing of the monolithic ceramic capacitor. The external electrodes of silver may also be coated sequentially with a layer of nickel or copper and a layer of solder or tin which are formed by plating. According to the present invention, the dielectric ceramics capacitor using the composition can be formed by firing at 1260-1300°C in a neutral or reducing atmosphere. Yet, it has an insulation resistance and an electrostatic capacity such that their product (CR product) is higher than 6000 Ω×F. This value changes only a little even in a high electric field. It has a high rated voltage with high reliability and exhibits a permittivity higher than 3000 even though the dielectric ceramic layers are made thinner. The dielectric ceramic composition of the present invention can be made into monolithic ceramic capacitors which have the above-mentioned characteristic properties and the temperature-dependent electrostatic capacity which meets the B specification of JIS and the X7R specification of EIA. These outstanding properties remain unchanged even at high temperatures under high humidity. The monolithic ceramic capacitor using the composition of the present invention has internal electrodes of nickel or nickel alloy. Therefore, it is less expensive than the conventional one that has internal electrodes of precious metal such as palladium. Yet, it exhibits good weather-resistance performance such as load characteristics at high temperatures under high humidity.

Claims: A dielectric ceramic composition which comprises a primary component and a secondary component in a molar ratio of from 100/0.5 to 100/5.0 and an auxiliary component in an amount of from 0.2 to 3.0 parts by weight for 100 parts by weight in total of said primary and secondary components, said primary component being composed of barium titanate containing less than 0.02 wt% of alkali metal oxide as an impurity, at least one of scandium oxide and yttrium oxide, at least one of samarium oxide and europium, oxide, and manganese oxide optionally containing cobalt oxide and/or nickel oxide, as expressed by the compositional formula below: (1 - α - β - γ){BaO} m ×TiO 2 + αM 2 O 3 + βRe 2 O 3 + γ(Mn 1-x-y Ni x Co y )O (where M 2 O 3 denotes Sc 2 O 3 or Y 2 O 3 or both, Re 2 O 3 denotes Sm 2 O 3 or Eu 2 O 3 or both, α, β, γ, m, x, and y are defined by: 0.0025 ≤ α + β ≤ 0.025 0 < β ≤ 0.0075 0.0025 ≤ γ ≤ 0.05 γ/(α + β) ≤ 4 0 ≤ x < 1.0 0 ≤ y < 1.0 0 ≤ x + y < 1.0 1.0000 < m ≤ 1.035 said secondary component being magnesium oxide (MgO), and said auxiliary component being an oxide represented by Li 2 O-(Si,Ti)O 2 -Al 2 O 3 -ZrO 2 . A dielectric ceramic composition according to Claim 1, characterized in that; said auxiliary component is represented by the general formula of pLi 2 O-q(Si z Ti 1-z )O 2 -rM (where p, q, and r denote the mol% of the respective constituents, z is defined by 0.30 ≤ z ≤ 1.0, M stands for Al 2 O 3 or ZrO 2 or both, and p, q, and r are within the area enclosed by the polygon having apexes defined as follows in the triangular coordinates: A (20, 80, 0) B (10, 80, 10) C (10, 70, 20) D (35, 45, 20) E (45, 45, 10) F (45, 55, 0) provided that 0.3 ≤ z < 1.0 for the composition corresponding to the line A-F. Use of the dielectric ceramic composition according to Claim 1 or 2 for a monolithic ceramic capacitor (1) comprising; a plurality of dielectric ceramic layers (3) made from said dielectric ceramic composition, a plurality of internal electrodes (2a, 2b, 2c, 2d) made from nickel or nickel alloy formed between said dielectric ceramic layers (3). Use of the dielectric ceramic composition according to Claim 1 or 2 for a monolithic ceramic capacitor (1) comprising; a plurality of dielectric ceramic layers (3) made from said dielectric ceramic composition, a plurality of internal electrodes (2a, 2b, 2c, 2d) made from nickel or nickel alloy formed between said dielectric ceramic layers (3) such that their edges show themselves from the ends of the dielectric ceramic layers (3), and external electrodes (4a,4b) electrically connected to the edges of said internal electrodes (2a, 2b, 2c, 2d). Use of the dielectric ceramic composition according to Claim 1 or 2 for a monolithic ceramic capacitor (1) comprising; a plurality of dielectric ceramic layers (3) made from said dielectric ceramic composition, a plurality of internal electrodes (2a, 2b, 2c, 2d) made from nickel or nickel alloy formed between said dielectric ceramic layers (3) such that their edges show themselves from the ends of the dielectric ceramic layers (3), and external electrodes (4a, 4b) electrically connected to the edges of said internal electrodes (2a, 2b, 2c, 2d), wherein said external electrodes (4a,4b) are constructed of sintered layers of electrically conductive metal powder containing or not containing glass frit. Use of the dielectric ceramic composition according to Claim 1 or 2 for a monolithic ceramic capacitor (1) comprising; a plurality of dielectric ceramic layers (3) made from said dielectric ceramic composition, a plurality of internal electrodes (2a, 2b, 2c, 2d) made from nickel or nickel alloy formed between said dielectric ceramic layers (3) such that their edges show themselves from the ends of the dielectric ceramic layers (3), and external electrodes (4a, 4b) electrically connected to the edges of said internal electrodes (2a, 2b, 2c, 2d), wherein said external electrodes (4a, 4b) are constructed of sintered layers of electrically conductive metal powder containing or not containing glass frit, and said sintered layers have a plated layer thereon.

Inventors: HARUNOBU SANO, HIROYUKI WADA, NORIHIKO SAKAMOTO, YUKIO HAMAJI, HARUNOBU, SANO, HIROYUKI, WADA, NORIHIKO, SAKAMOTO, YUKIO, HAMAJI
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1997
Main classification: H01G4
IPC codes: H01G4, C04B35, H01B3