DIELECTRIC CERAMIC COMPOSITION

Abstract: A dielectric ceramic composition possessing a high dielectric constant and a high unloaded Q and exhibiting stable electric properties even in the high frequency range of 10 GHz contains not less than 59.0 mol% and not more than 66.0 mol% of BaO, less than 10 mol% of ZnO, less than 10 mol% of MgO, less than 10 mol% of NiO, less than 10 mol% of ZrO₂, and not less than 19.0 mol% and less than 24 mol% of Ta₂O₅.

Description: This invention relates to a dielectric ceramic composition which possesses a high dielectric constant and a high unloaded Q and exhibits stable temperature properties. Generally in dielectric resonators and dielectric substrates used as incorporated in signal circuits operating in the high frequency region such as of microwave and millimeter wave, dielectric ceramics possessing a high dielectric constant and a high unloaded Q and exhibiting stable temperature properties find utility. Heretofore, as dielectric ceramics of this kind, dielectric ceramics of the Ba(Zn-Ta)O type [Japanese Patent Publication SHO 59(1984)-48,484], the Ba(Zn-Nb)O type [Japanese Patent Publication SHO 59(1984)-48,483], the Ba(Zn-Ta-Nb)O type [Japanese Patent Publication SHO 59(1984)-23,044], the Ba(Mg-Ni-Ta)O type [Japanese Patent Application Disclosure SHO 60(1985)-216,407], and the Ba(Mg-Co-Ta)O type [Japanese Patent Application Disclosure SHO 61(1986)-8,804] have been proposed. The dielectric ceramics of the compositions disclosed in the three Japanese Patent Publications mentioned above have a high dielectric constant of the order of 30 to 40 and yet offer a small unloaded Q of about 5,000 in the high frequency region of about 10 GHz. The dielectric ceramics of the compositions disclosed in the two Japanese patent application disclosures mentioned above indeed have a large unloaded Q of about 8,000 and yet offer a low dielectric constant on the order of 25. Thus, they have a problem that they do not fulfil the requirement for a higher unloaded Q and a larger dielectric constant which the dielectric ceramic articles used in communication devices are expected to possess in keeping pace with the gradual advance in performance of such communication devices in recent years. It is, therefore, an object of this invention to provide a dielectric ceramic composition which is freed from the problem mentioned above and allowed to possess a high unloaded Q and a large dielectric constant and exhibit stable temperature properties even in the high frequency region of 10 GHz. The inventors continued a diligent study for the purpose of solving the problem mentioned above and accomplishing the object mentioned above. They have consequently found that the object is fulfilled by an oxide composition containing Ba, Zn, Mg, Ni, Zr, and Ta in specified proportions. The present invention has been completed as the result. To be specific, this invention is directed to a dielectric ceramic composition containing not less than 59.0 mol% and not more than 66.0 mol% of BaO, less than 10 mol% of ZnO, less than 10 mol% of MgO, less than 10 mol% of NiO, less than 10 mol% of ZrO₂, and not less than 19.0 mol% and less than 24 mol% of Ta₂O₅. For the components of the composition of this invention, the corresponding oxide powders to be used are desired each to have a purity of about 99.9% by weight. The unloaded Q is lowered if the proportion of BaO is less than 59.0 mol% or more than 66.0 mol%. The unloaded Q is similarly lowered if the proportion of ZnO exceeds 10 mol%. The dielectric constant is lowered or the unloaded Q is lowered if the ZnO content is absent. The dielectric constant is lowered if the proportion of MgO exceeds 10 mol%. The unloaded Q is low if the MgO content is absent. The unloaded Q is lowered if the proportion of NiO exceeds 10 mol%. The temperature coefficient of resonant frequency is unduly large on the positive side if the NiO content is absent. The temperature coefficient unduly increases if the proportion of ZrO₂ exceeds 10 mol%. The dielectric constant is lowered if the ZrO₂ content is absent. The unloaded Q is lowered if the proportion of Ta₂O₅ deviates from the range of not less than 10 mol% and less than 24 mol%. Hence, the aforementioned ranges for the component oxides mentioned above are required. The raw material powder prepared by combining the component oxides in the ratio described above is mixed with pure water in a pot made of resin with the aid of resin-coated balls for a period of 10 to 20 hours. The resultant mixture is dried at a temperature in the range of 100° to 150°C for a period in the range of one to three hours. The dried mixture is then calcined in an atmosphere of oxygen or in the air at a temperature in the range of 1,000° to 1,300°C for a period in the range of one to five hours. The product of calcination is pulverized into particles 420 µm - 150 µm (40 to 100 mesh) in diameter. The resultant powder is molded in a prescribed shape in a hydrostatic press under a pressure of 9.80 x 10⁷ - 1.96 x 10⁸ Pa (1 to 2 t/cm²). The product aimed at is obtained by firing the molded pass in an atmosphere of oxygen or in the air at a temperature in the range of 1,450° to 1,650°C for a period in the range of two to ten hours. Now, the present invention will be described more specifically below with reference to working examples. Examples 1 to 9: As raw materials, powders of barium carbonate, zinc oxide, magnesium oxide, nickel oxide, zirconium oxide, and tantalum oxide each of a purity of 99.9% by weight were weighed out in amounts calculated to permit production of dielectric ceramic particles of compositions shown in Table 1. Each of the raw materials so weighed out was placed in conjunction with pure water in a pot made of resin and mixed therein with the aid of resin-coated balls for a period of 16 hours. The resultant mixture was dried at 150°C for three hours and then calcined in an atmosphere of oxygen at a temperature in the range of 1,000° to 1,200°C for two hours. The product of this calcination was pulverized and then passed through a 355 µm (42-mesh) sieve for unification of particle diameter. In a metallic die, the resultant powder was subjected to primary molding in the shape of a disk 10 mm in diameter and 5 mm in thickness under a pressure of 4.9 x 10⁷ Pa (500 kg/cm²) and then press molded in a prescribed shape in a hydrostatic press under a pressure of 1.96 x 10⁸ Pa (2,000 kg/cm²). The shaped mass thus obtained was fired in an atmosphere of oxygen at a temperature in the range of 1,500° to 1,650°C for a period of four hours, to obtain a dielectric ceramic article. The dielectric ceramic article was tested for dielectric constnat (εr), unloaded Q (Q o ), and temperature coefficient (τf) of resonant frequency by the dielectric rod resonator method using a frequency of about 10 GHz. The results were as shown in Table 1. Comparative Experiments 1 to 10: Dielectric ceramic articles of compositions shown in Table 1 were produced by following the procedure of Example 1 and they were tested for the same properties as mentioned above in the same manner as in Example 1. The results were as shown in Table 1. This invention brings about the truly conspicuous effect of permitting production of a heretofore unattainable dielectric ceramic composition excelling in dielectric constant and unloaded Q and in stability of temperature properties because it contains Ba, Zn, Mg, Ni, Zr, and Ta in specific proportions.

Claims: A dielectric ceramic composition, characterized by containing not less than 59.0 mol% and not more than 66.0 mol% of BaO, more than O but less than 10 mol% of ZnO, more than O but less than 10 mol% of MgO, more than O but less than 10 mol% of NiO, more than O but less than 10 mol% of ZrO₂, and 19.0 to less than 24 mol% of Ta₂O₅. A composition according to claim 1, wherein the component oxides each possess purity of approximately 99.9% by weight. A process for producing a dielectric ceramic article using a composition according to claim 1 comprising mixing raw materials for the component oxides with pure water, drying and calcining the resultant mixture, pulverizing the product of the calcination into particles 150 - 420 µm (40 to 100 mesh) in diameter, and moulding the resultant powder into a prescribed shape under pressure in the range of 9.8 x 10⁷ - 1.96 x 10⁸ Pa (1 to 2 t/cm²) and firing the moulded mass. A process according to claim 3, wherein the mixing is carried out with the aid of resin-coated balls. A process according to claim 3, wherein the drying is carried out at a temperature in the range of 100° to 150°C for a period in the range of one to three hours and the calcination at a temperature in the range of 1,000° to 1,300°C for a period in the range of one to five hours. A process according to claim 3, wherein the pressure moulding is carried out with a hydrostatic press. A process according to claim 3, wherein the firing is carried out at a temperature in the range of 1,450° to 1,650°C for a period of two to ten hours.

Inventors: HYUGA, TAKEHIRO, MATSUMOTO, KAZUTOSHI, MUKAI, TETSUYA
Applicants: SUMITOMO METAL MINING COMPANY LIMITED
Application year: 1989
Main classification: C04B35
IPC codes: H01P11, C04B35, H01B3, H01P7