Microwave dielectric ceramic composition

Abstract: Disclosed herein is a microwave dielectric ceramic composition which comprises as the main ingredient, a composition represented by xMgTiO₃ ·(1-x)CaTiO₃ (0.93 ≦ x ≦ 0.95), to which 3-9wt% of ZnO, 2-4wt% of Ta₂O₅, 1-6wt% of Nb₂O₅,0.1-6wt% of MnO₂, 3-12wt% of Al₂O₃ or 3-12wt% of Co₂O₃ to xMgTiO₃ ·(1-x)CaTiO₃. And the microwave dielectric ceramic compositions have a Qu value in the range of 3000 to 4600 (at 6 GHz), a temperature coefficient of the resonance frequency(τf) in the range of -10 to +10 ppm/°C and relative dielectric constant(ε r ) in the range of 18 to 22. The dielectric ceramic compositions are capable of reducing τf approximately to zero or optionally and stably controlling τf to a desired value both to positive and negative sides around zero as the center while maintaining ε r and Qu within practical characteristic ranges by controlling the addition (constitution) ratio of the specified oxides. Further, even if the sintering temperature is changed within a wide range, the sintering products of high density and high quality can be attained due to the addition of the specified oxides.

Description: Background of the Invention The present invention concerns a microwave dielectric ceramic composition and, more specifically, it relates to a microwave dielectric ceramic composition capable of reducing the temperature coefficient of resonance frequency (hereinafter simply referred to as τf) while maintaining unloaded Q (hereinafter simply referred to as Qu) and, further, capable of optionally controlling τf to positive and negative sides around zero as the center by controlling the mixing ratio of CaTiO 3 or a specified oxide. The present invention also relates to a microwave dielectric ceramic composition having high quality even if it is sintered at a low temperature due to the addition of a specified oxide or with less scattering in the quality even if it is sintered in a wide temperature range. The present invention is applicable to impedance matching or the like of dielectric resonators, microwave integrated circuit boards and various kinds of microwave circuits in the microwave region. Since the dielectric loss of a microwave dielectric ceramic composition (hereinafter simply referred to as a dielectric ceramic composition) tends to increase as the working frequency increases, a dielectric ceramic composition of high Qu in a microwave frequency region has been demanded. As conventional dielectric ceramic materials, a dielectric ceramic composition of a crystal structure containing two phases, that is, a perovskite phase and an ilmenite phase (Japanese Patent Laid-Open Hei 2-129065) and a dielectric ceramic composition containing a predetermined amount of CaTiO 3 in MgTiO 3 and TiO 2 (Japanese Patent Laid-Open Sho 52-118599) have been known. However, the former dielectric ceramic composition contained other ingredients such as Nd 2 O 3 , La 2 O 3 , PbO, ZnO in a great amount and, in addition, the value Qu is not always high. The latter dielectric ceramic composition contains TiO 2 as the essential ingredient and τf changes greatly as from +87 to -100 within a range for the mixing amount of CaTiO 3 from 3 to 10 % by weight to cause difficulty in controlling τf to be a small value around zero. The present invention intends to solve the foregoing problem and it is an object of the present invention to provide a dielectric ceramic composition capable of reducing τf approximately to zero or optionally and stably controlling τf to a desired value both to positive and negative sides around zero as the center while maintaining ε r (relative dielectric constant) and Qu within practical characteristic ranges by controlling the addition (constitution) ratio of specified oxides (ZnO, Ta 2 O 5 , Nb 2 O 5 , MnO 2 , Al 2 O 3 or Co 2 O 3 ) and, further, having a high quality even if it is sintered at a low temperature or even if even if it is sintered in a wide temperature range due to the addition of a specified oxide. Summary of the Invention The present inventor has made various studies on a composition of a dielectric ceramic composition capable of bringing τf to approach zero while maintaining a high Qu value and having stable quality even if sintering temperature varies and, as a result, has accomplished the present invention based on the finding that the foregoing drawback can be overcome by adjusting the addition ratio of CaTiO 3 and specified oxide. Namely, the dielectric ceramic composition according to the present invention comprises, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTiO 3 (0.925 ≦ x ≦ 0.950), to which 3 to 9 parts by weight (hereinafter referred to as % by weight) of ZnO is added and incorporated based on 100 parts by weight of xMgTiOa ·(1-x)CaTiO 3 . If x is smaller than 0.925, τf takes a large positive value and Qu is lowered, whereas τf takes a large negative value if x exceeds 0.950, which are not preferred. In particular, it is preferred that x is from 0.935 to 0.945 and the addition amount of ZnO is 6% by weight, since Qu is from 3900 to 4100, τf is -5 to +5 (ppm/ °C) and ε r is about 21, high quality can be ensured even by sintering at a low temperature and stability to the sintering temperature is obtained. As the mixing ratio of CaTiO 3 increases, τf increases from negative to positive (Fig. 3) and ε r increases (Fig. 2), while Qu tends to decrease (Fig. 1). Further, as shown in Fig. 7, a sintering product of high density can be produced even by sintering at a low temperature (for example, at 1325 to 1350 °C) and, accordingly, stable quality can be attained even if the sintering temperature changes variously (or even if sintering is conducted at a low temperature)(Figs 4-11). In view of the above, within an appropriate mixing range for CaTiO 3 and ZnO described above, a balance is attained for the characteristics and stable quality can be obtained. The dielectric ceramic composition according to another aspect of the present invention comprises, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x) CaTiO 3 (in which 0.923≦ x ≦ 0.940), to which 2 to 4 parts by weight (hereinafter referred to as % by weight) of Ta 2 O 5 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . If x is smaller than 0.923, τf takes a large positive value and Qu decreases, whereas if x exceeds 0.940, τf takes a large negative value, which are not preferred. Particularly, it is preferred that x is from 0.927 to 0.935 and the addition amount of Ta 2 O 5 is 3% by weight, since Qu is from 3920 to 4260, τf is from -8.5 to +2.3 (ppm/°C), ε r is from 19.7 to 21.6 and the scattering in the characteristics is extremely small even if sintering temperature is varied. As the mixing ratio of CaTiO 3 increases, τf increases from a negative to a positive value (Fig. 16), ε r increases (Fig. 15), while Qu tends to decrease (Fig. 14). Further, as shown in Fig. 23, sintering products at high density can be produced even if sintering is applied at a low temperature (for example, at 1300-1325 °C) due to the addition of Ta 2 O 5 . Further, products of stable quality can be obtained if the sintering temperature is varied within a range of 1300 to 1400 °C (Figs. 17-23). In view of the above, within the appropriate mixing range of CaTiO 3 and Ta 2 O 5 described above, the characteristics are well-balanced and products of stable quality can be obtained. The dielectric ceramic composition according to another aspect of the present invention comprises, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x) CaTiO 3 (in which 0.925≦ x≦ 0.940), to which 1 to 6 parts by weight (hereinafter referred to as % by weight) of Nb 2 O 5 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . If x is smaller than 0.925, τf takes a large positive value and Qu decreases, whereas τf takes a large negative value if x exceeds 0.940, which are not preferred. Particularly, it is preferred that x is 0.930 and the addition amount of Nb 2 O 5 is 2% by weight, since Qu is from 3980 to 4320 τf is from -3.69 to +0.52 ppm/ °C and ε r is from 19.05 to 21.5 when sintering is applied at 1275-1400°C, and products of high quality can be obtained stably even if sintering is applied within a wide temperature range. As the mixing ratio of CaTiO 3 increases, τf increases from a negative to a positive value (Fig. 28), ε r increases (Fig. 27), while Qu tends to decrease (Fig. 26). Further, as shown in Figs. 29 - 31 although Qu and τf do not vary so much, but τf tends to decrease due to the addition of Nb 2 O 5 . Particularly, at the mixing ratio of CaTiO 3 of 0.07, the addition amount of Nb 2 O 5 of about 2% by weight is extremely preferred since τf is about 0 ppm/ °C. Further, as shown in Figs. 32-36 and Tables 5 and 6, sintering products of stable performance and high sintering density can be produced even if sintering is applied within a wide temperature range. Accordingly, addition amount of Nb 2 O 5 , particularly, of 1 to 4% by weight, (more particularly, about 2% by weight) is excellent in view of further excellent balance of performance and stable sintering product. In view of the above, within the appropriate mixing range of CaTiO 3 and Nb 2 O 5 described above, products of excellent performances with excellent balance and of stable quality can be obtained. The dielectric ceramic composition according to other aspect of the present invention comprises, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x) CaTiO 3 (in which 0.93 ≦ x≦ 0.95), to which 0.1 to 6 parts by weight (hereinafter referred to as % by weight) of MnO 2 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . If x is smaller than 0.93, τf takes a large positive value and Qu decreases, whereas τf takes a large negative value if x exceeds 0.95, which are not preferred. Particularly, if x is 0.94 and the addition amount of MnO 2 is 3 to 6% by weight, Qu is from 3080 to 3890, τf is from -2.60 to +1.78 ppm/ °C, and ε r is from 19.04 to 20.95 when sintering is applied at 1350-1425 °C as shown in Table 8, and products of high quality can be obtained even if sintering is applied with in a wide temperature range. As the mixing ratio of CaTiO 3 increases, τf increases from a negative to a positive value (Table 7, Figs. 40, 44, 48), ε r increases (Table 7, Figs. 39, 43, 47), while Qu tends to decrease (Table 7, Figs. 38, 42 and 46). Further, in the case of adding MnO 2 , Qu tends to decrease (Fig. 38), ε r (within a range of 1375 to 1425 °C) shows no substantial change (Fig. 39), τf tends to decrease (Figs. 40, 48) and the sintering density tends to increase (Figs. 41, 49). Particularly, at the mixing ratio of CaTiO 3 is 0.06, the addition amount of MnO 2 of about 3% by weight is extremely preferred since τf is about 0 ppm/ °C even if the sintering temperature is greatly varied as 1325 to 1425°C as shown in Fig. 40. Further, as shown in Figs. 38-49 and Tables 8-10, sintering products with stable performance and high sintering density can be produced even if sintering is applied within a wide temperature range (particularly from 1375 to 1425 °C). Further, in a case where the mixing ratio of CaTiO 3 is 0.05, τf is as small as about -10 ppm/ °C even within the range for the addition amount of MnO 2 from 0.1 to 0.6. On the other hand, in a case where the mixing ratio of CaTiO 3 is 0.07, τf is as large as +10 ppm/ °C within the addition amount range of MnO 2 of 3 to 6% by weight. Accordingly, the mixing ratio of CaTiO 3 of about 0.06 and the addition amount of MnO 2 , particularly, of 1 to 6% by weight (more particularly, about 3% by weight) are more excellent in view of further excellent balance of performance and stable sinterability. In view of the above, within the appropriate mixing range of CaTiO 3 and MnO 2 described above, products of excellent, well-balanced performance and of stable quality can be obtained. The dielectric ceramic composition according to another aspect of the present invention comprises, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x) CaTiO 3 (in which 0.93 ≦ x ≦ 0.95), to which 3 to 12 parts by weight (hereinafter referred to as % by weight) of Al 2 O 3 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . If x is smaller than 0.93, τf takes a large positive value and Qu decreases, whereas τf takes a large negative value if x exceeds 0.95, which are not preferred. As the addition amount of Al 2 O 3 increases Qu tends to increase (Fig. 51), and ε r , τf and the sintering density tend to decrease (Figs. 52-54). Particularly, if the addition amount of Al 2 O 3 is 3 to 9% by weight and the sintering temperature is from 1300 to 1375°C, Qu is 3360 to 3730, ε r is 18.4 to 20.6, τf is -2.2 to +2.6 ppm/°C, the sintering density is 3.57 to 3.82 g/cm 3 as shown in Table 11 and Figs. 51-54, and products of high quality can be obtained stably even if sintering is applied within a wide temperature range. Particularly, τf scarcely fluctuates (namely, concentrating to -2 - +3 ppm/°C) and shows a value around 0 in each of the cases. In view of the above, products of excellent performance described above and excellent balance thereof and of stable quality can be obtained by the addition amount of Al 2 O 3 (3-9% by weight) and in a wide and appropriate sintering temperature range (1300-1375 °C). The dielectric ceramic composition according to another aspect of the present invention comprises, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x) CaTiO 3 (in which 0.93 ≦x ≦ 0.95), to which 3 to 12 parts by weight (hereinafter referred to as % by weight) of Co 2 O 3 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . If x is smaller than 0.93, τf takes a large positive value and Qu decreases, whereas τf takes a large negative value if x exceeds 0.95, which are not preferred. If the addition amount of Co 2 O 3 is less than 3% by weight, τf increases toward the positive side and Qu decreases if the addition amount exceeds 12% by weight, which are not preferred. On the other hand, if the addition amount is from 3 to 12% by weight, τf can be reduced to a value around zero while concentrating Qu and ε r within practical ranges with no substantial reduction. Then, as the mixing ratio of CaTiO 3 increases, it tends to decrease Qu, increase ε r and turn τf from a negative to a positive value (Table 7). Further, as the addition amount of Co 2 O 3 increases, Qu tends to decrease (Fig. 64), ε r tends to decrease slightly although shows no substantial change (Fig. 65), τf tends to turn to the negative side (Fig. 66) and the sintering density tends to increase (Fig. 67). Particularly, if the addition amount of Co 2 O 3 is 6 wt% and sintering is applied at 1350 to 1450 °C, Qu is 3780 to 3970, τf is -0.74 to -0.03 ppm/°C, ε r is 20.4 to 20.8 and the sintering density is 3.83 to 3.89 g/cm 3 as shown in Table 12 and Figs. 64-71, and each of the performances less scatters and excellent performances is exhibited even sintering is applied within a wide temperature range of 100 °C. In particular, τf takes an extremely small absolute value around 0 ppm/ °C and shows a value of about 0.5 (ppm/°C)/ 1wt% of Co 2 O 3 , and fine control for τf can be done extremely easily. In view of the above, products having such excellent, well-balanced performance, as well as capable of easy fine control for τf and of stable quality can be attained by the addition amount of Co 2 O 3 and in a wide and appropriate sintering temperature range. As has been described above, in the dielectric ceramic composition according to the present invention, τf can be brought to approach zero or optionally controlled to a desired value between both positive and negative sides around 0(zero) as a center by controlling the blending ratio of CaTiO 3 while maintaining Qu and ε r within practical (high) ranges of characteristics, as well as τf being controlled stably around 0(zero). Further, even if the sintering temperature is changed within a wide range, sintering products of high density and high quality can be attained due to the addition of ZnO 2 , Ta 2 O 5 , Nb 2 O 5 , MnO 2 , Al 2 O 3 or Co 2 O 3 . In the case of adding ZnO, sintering products of high quality can be obtained even if sintering is applied at a relatively low temperature. Further, in a case of adding Co 2 O 3 , τf can be finely controlled easily. Accordingly, the mixing ratio of CaTiO 3 and specific oxides (ZnO and so on) can be varied depending on the purpose. Brief Description of the Drawings Fig. 1 is a graph showing the relation between x and Qu in a (xMgTiO 3 ·(1-x)CaTiO 3 + 6 wt% ZnO) ceramic composition produced at a sintering temperature of 1350 °C. Fig. 2 is a graph showing the relation between x and ε r in the ceramic composition shown in Fig. 1. Fig. 3 is a graph showing the relation between x and τf in the ceramic composition shown in Fig. 1. Fig. 4 is a graph showing the relation between the amount of ZnO and Qu in a (0.94MgTiO 3 ·0.06CaTiO 3 + (0-9) wt% ZnO) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 5 is a graph showing the relation between the amount of ZnO and ε r in the ceramic composition shown in Fig. 4. Fig. 6 is a graph showing the relation between the amount of ZnO and τf in the ceramic composition shown in Fig. 4. Fig. 7 is a graph showing the relation between the amount of ZnO and the sintering density in the ceramic composition shown in Fig. 4. Fig. 8 is a graph showing the relation between the sintering temperature and Qu in the (0.94MgTiO 3 ·0.06CaTiO 3 + (0-9) wt% ZnO) ceramic composition. Fig. 9 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 8. Fig. 10 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 8. Fig. 11 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 8. Fig. 12 is a graph showing the result of X-ray diffraction of a (0.95MgTiO 3 ·0.05CaTiO 3 + 6 wt% ZnO) ceramic composition. Fig. 13 is a graph showing the result of X-ray diffraction of a (0.95MgTiO 3 ·0.05CaTiO 3 ) ceramic composition. Fig. 14 is a graph showing the relation between x and Qu in a (xMgTiO 3 ·(1-x)CaTiO 3 + 3wt% Ta 2 O 5 ) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 15 is a graph showing the relation between x and ε r in the ceramic composition shown in Fig. 14. Fig. 16 is a graph showing the relation between x and τf in the ceramic composition shown in Fig. 14. Fig. 17 is a graph showing the relation between the amount of Ta 2 O 5 and Qu in a (0.93MgTiO 3 ·0.07CaTiO 3 + (2-4) wt% Ta 2 O 5 ) ceramic composition produced by sintering at each of sintering temperatures. Fig. 18 is a graph showing the relation between the amount of Ta 2 O 5 and ε r in the ceramic composition shown in Fig. 17. Fig. 19 is a graph showing the relation between the amount of Ta 2 O 5 and τf in the ceramic composition shown in Fig. 17. Fig. 20 is a graph showing the relation between the sintering temperature and Qu in the (0.93MgTiO 3 ·0.07CaTiO 3 + (0-4) wt% Ta 2 O 5 ) ceramic composition. Fig. 21 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 20. Fig. 22 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 20. Fig. 23 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 20. Fig. 24 is a graph showing the result of X-ray diffraction of a xMgTiO 3 ·(1-x)CaTiO 3 + 3wt% Ta 2 O 5 , the sintering temperature: 1300°C) ceramic composition. Fig. 25 is a graph showing the result of X-ray diffraction of a xMgTiO 3 ·(1-x)CaTiO 3 + 3wt% Ta 2 O 5 , the sintering temperature: 1350°C) ceramic composition. Fig. 26 is a graph showing the relation between x and Qu in a (xMgTiO 3 ·(1-x)CaTiO 3 + 2wt% Nb 2 O 5 ) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 27 is a graph showing the relation between x and ε r in the ceramic composition shown in Fig. 26. Fig. 28 is a graph showing the relation between x and τf in the ceramic composition shown in Fig. 26. Fig. 29 is a graph showing the relation between the amount of Nb 2 O 5 and Qu in a (0.93MgTiO 3 ·0.07CaTiO 3 + (0-6) wt% Nb 2 O 5 ) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 30 is a graph showing the relation between the amount of Nb 2 O 5 and ε r in the ceramic composition shown in Fig. 29. Fig. 31 is a graph showing the relation between the amount of Nb 2 O 5 and τf in the ceramic composition shown in Fig. 29. Fig. 32 is a graph showing the relation between the amount of (0-6 wt%) Nb 2 O 5 and the sintering density in the ceramic composition shown in Fig. 29. Fig. 33 is a graph showing the relation between the sintering temperature and Qu in the (0.93MgTiO 3 ·0.07CaTiO 3 + (1-6) wt% Nb 2 O 5 ) ceramic composition. Fig. 34 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 33. Fig. 35 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 33. Fig. 36 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 33. Fig. 37 is a graph showing the result of X-ray diffraction of a (0.93MgTiO 3 ·0.07CaTiO 3 + (2, 4 or 6wt%) Nb 2 O 5 ) ceramic composition. Fig. 38 is a graph showing the relation between the amount of MnO 2 and Qu in a (0.94MgTiO 3 ·0.06CaTiO 3 + 0-6wt% MnO 2 ) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 39 is a graph showing the relation between the amount of MnO 2 and ε r in the ceramic composition shown in Fig. 38. Fig. 40 is a graph showing the relation between the amount of MnO 2 and τf in the ceramic composition shown in Fig. 38. Fig. 41 is a graph showing the relation between the amount of 0-6wt% MnO 2 and the sintering density in the ceramic composition shown in Fig. 38. Fig. 42 is a graph showing the relation between the sintering temperature and Qu in the (0.95MgTiO 3 ·0.05CaTiO 3 + (0-0.6) wt% MnO 2 ) ceramic composition. Fig. 43 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 42. Fig. 44 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 42. Fig. 45 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 42. Fig. 46 is a graph showing the relation between the sintering temperature and Qu in the (0.93MgTiO 3 ·0.07CaTiO 3 + (0-6) wt% MnO 2 ) ceramic composition. Fig. 47 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 46. Fig. 48 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 46. Fig. 49 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 46. Fig. 50 is a graph showing the result of X-ray diffraction of a (0.94MgTiO 3 ·0.06CaTiO 3 + (0, 3 or 6wt%) MnO 2 ) ceramic composition. Fig. 51 is a graph showing the relation between the amount of Al 2 O 3 and Qu in a (0.94MgTiO 3 ·0.06CaTiO 3 + 0-12wt% Al 2 O 3 ) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 52 is a graph showing the relation between the amount of Al 2 O 3 and ε r in the ceramic composition shown in Fig. 51. Fig. 53 is a graph showing the relation between the amount of Al 2 O 3 and τf in the ceramic composition shown in Fig. 51. Fig. 54 is a graph showing the relation between the amount of 3-12wt% Al 2 O 3 and the sintering density in the ceramic composition shown in Fig. 51. Fig. 55 is a graph showing the relation between the sintering temperature and Qu in the (0.94MgTiO 3 ·0.06CaTiO 3 + (3-12) wt% Al 2 O 3 ) ceramic composition. Fig. 56 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 55. Fig. 57 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 55. Fig. 58 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 55. Fig. 59 is a graph showing the relation between the amount of Al 2 O 3 and the average grain size of the sintering product in the (0.94MgTiO 3 ·0.06CaTiO 3 + 3-12wt% Al 2 O 3 ) ceramic composition produced at a sintering temperature of 1350 °C. Fig. 60 is a graph showing the relation between the sintering temperature and the average grain size of the sintering product in the (0.94MgTiO 3 ·0.06CaTiO 3 + 12wt% Al 2 O 3 ) ceramic composition produced at a sintering temperature of 1350 °C. Fig. 61 is the electron microscopic photograph (1000 magnification ratio) which explains the structure of crystals of the (0.94MgTiO 3 ·0.06CaTiO 3 + 6wt% Al 2 O 3 ) ceramic composition. Fig. 62 is the electron microscopic photograph (1000 magnification ratio) which explains the structure of crystals of the (0.94MgTiO 3 ·0.06CaTiO 3 + 12wt% Al 2 O 3 ) ceramic composition. Fig. 63 is a graph showing the result of X-ray diffraction of a (0.94MgTiO 3 ·0.06CaTiO 3 + 3, 6, 9 or 12wt% Al 2 O 3 ) ceramic composition. Fig. 64 is a graph showing the relation between the amount of Al 2 O 3 and Qu in a (0.94MgTiO 3 ·0.06CaTiO 3 + 3-12wt% Co 2 O 3 ) ceramic composition produced by sintering at each of the sintering temperatures. Fig. 65 is a graph showing the relation between the amount of 3-12wt% Co 2 O 3 and ε r in the ceramic composition shown in Fig. 64. Fig. 66 is a graph showing the relation between the amount of 3-12wt% Co 2 O 3 and τf in the ceramic composition shown in Fig. 64. Fig. 67 is a graph showing the relation between the amount of 3-12wt% Co 2 O 3 and the sintering density in the ceramic composition shown in Fig. 64. Fig. 68 is a graph showing the relation between the sintering temperature and Qu in the (0.94MgTiO 3 ·0.06CaTiO 3 + 3-12wt% Co 2 O 3 ) ceramic composition. Fig. 69 is a graph showing the relation between the sintering temperature and ε r in the ceramic composition shown in Fig. 68. Fig. 70 is a graph showing the relation between the sintering temperature and τf in the ceramic composition shown in Fig. 68. Fig. 71 is a graph showing the relation between the sintering temperature and the sintering density in the ceramic composition shown in Fig. 68. Fig. 72 is a graph showing the relation between the sintering temperature and the average grain size in the ceramic composition shown in Fig. 68. Fig. 73 is a graph showing the result of X-ray diffraction of a (0.94MgTiO 3 ·0.06CaTiO 3 + 3, 6 or 12wt% Co 2 O 3 ) ceramic composition. Description of the preferred Embodiments Now, the present invention will be explained specifically by way of examples. Example 1 MgO powder (99.4% purity), CaCO 3 powder for CaO (99% purity), TiO 2 powder (99.98% purity) and ZnO powder (99.5% purity) as the starting material were weighed each by a predetermined amount (about 600 g in total) and mixed so as to provide a composition in which each of x and y varies in the formula xMgTiO 3 ·(1-x)CaTiO 3 + y wt% ZnO (in which y represents parts by weight of ZnO based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 ) as shown in Table 1 and Figs. 1-4. Then, after dry mixing in a mixer (20 to 30 min.) and primary pulverization, they were calcined in atmospheric air at a temperature of 1100 °C for 2 hours. Subsequently, an appropriate amount of an organic binder (29g) and water (300-400g) was added to the calcined powder, which was pulverized together with alumina balls of 20 mm⊘ at 90 rpm for 23 hours. Then, the pulverized powder was pelletized in vacuum freeze drying (about 53.3 Pa (0.4 Torr), at 40-50 °C for about 20 hours), and the thus pelletized raw material was molded into a cylindrical shape of 19 mm ⊘ x 11 mmt (thickness) under a pressing pressure of 1,000 kg/cm 2 . Subsequently, the molding product was degreased in atmospheric air at 500°C for 3 hours and then sintered at temperatures within the range of 1300 to 1425 °C [xMgTiO 3 ·(1-x)CaTiO 3 +0∼9wt%ZnO] ceramic composition No. x Amount of ZnO (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0.950 0 1100 1350 3540 19.00 -21.1 - 2 0.950 3 1100 1350 4030 20.48 -10.4 3.863 3 0.950 6 1100 1350 4090 20.39 -14.1 3.911 4 0.950 9 1100 1350 - - - - 5 0.9475 0 1100 1350 2880 16.80 -16.9 3.386 6 0.9475 3 1100 1350 4270 20.05 - 5.07 3.792 7 0.9475 6 1100 1350 4300 20.13 - 9.71 3.847 8 0.9475 9 1100 1350 4360 20.05 -14.7 3.895 9 0.943 0 1100 1350 3030 17.16 -11.4 3.394 10 0.943 3 1100 1350 4370 19.49 - 7.26 3.710 11 0.943 6 1100 1350 4140 20.38 - 5.01 3.849 12 0.943 9 1100 1350 4210 20.47 - 8.50 3.906 13 0.940 0 1100 1350 3820 18.27 0.19 3.480 14 0.940 3 1100 1350 3720 21.52 19.0 3.834 15 0.940 6 1100 1350 4000 20.94 0.50 3.888 16 0.940 9 1100 1350 3680 21.56 15.3 3.944 17 0.935 0 1100 1350 3890 18.39 7.85 3.467 18 0.935 3 1100 1350 3530 21.39 21.9 3.798 19 0.935 6 1100 1350 3900 21.25 5.32 3.893 20 0.935 9 1100 1350 3640 21.83 17.2 3.954 21 0.930 0 1100 1350 3820 19.54 15.1 3.577 22 0.930 3 1100 1350 3610 21.02 17.2 3.789 23 0.930 6 1100 1350 3690 21.64 16.6 3.896 24 0.930 9 1100 1350 3780 21.55 8.86 3.942 25 0.925 0 1100 1350 3110 18.82 17.3 3.467 26 0.925 3 1100 1350 3600 21.13 21.6 3.758 27 0.925 6 1100 1350 3670 21.92 21.1 3.897 28 0.925 9 1100 1350 3660 21.89 16.6 3.948 shown in each of the figures for 4 hours and, finally, both end faces were polished to form cylindrical members each of about 16mm⊘ x 8 mmt (thickness) as dielectric specimens. Then, measurement was conducted for each of the specimens, regarding ε r (relative dielectric constant), Qu and τf by a parallel plate dielectric cylindrical resonator method (TE 011 MODE) or the like and, further, sintering density by an Archimedes method. τf was measured in a temperature region of 20°C to 80°C and calculated as τf = ((f(80°C) - f(20 °C))/(f (20 °C) x ΔT ). ΔT: 80 °C - 20 °C = 60 °C. The resonance frequency is 6 GHz. The results are shown in Figs. 1-11. As an example, results of X-ray diffraction is shown for the case of 0.95 MgTiO 3 ·0.05 CaTiO 3 in Fig. 12 (containing 6% by weight of ZnO based on 0.95 MgTiO 3 ·0.05 CaTiO 3 , sintered at 1300 °C for 4 hours) and in Fig. 13 (not containing ZnO, sintered at 1360°C for 4 hours). As can be seen from the results, the value Qu tends to decrease if x in xMgTiO 3 ·(1-x)CaTiO 3 is small, whereas τf and ε r tend to increase toward the positive side. The sintering density tends to increase as the sintering temperature is higher, whereas it becomes flat relative to the sintering temperature as the addition amount of ZnO is increased. At a sintering temperature of 1350 to 1425°C, a preferred range for x is from 0.925 to 0.950, since practical characteristic ranges are shown for τf as + 23 to -17 ppm/ °C, for ε r as 19 to 22 and for Qu as 3330 to 4390. Particularly, if x = 0.940 and the addition amount of ZnO is 6% by weight, at a sintering temperature, for example, of 1350°C and 1375 °C, a particularly excellent balance of characteristics is shown in Fig. 1 to Fig. 6, in which τf is from -1 to +1 ppm/ °C, ε r is about 2.1 and Qu is about 4000. Further, with regard to τf, since the variation coefficient relative to the sintering temperature is low, a small value around 0 can be adjusted easily. On the other hand, it is not preferred that CaTiO 3 is not contained since the value Qu is large but ε r is small and τf remarkably decreases toward the negative side to -25 to -44 ppm/ °C. Further, the analysis method based on the absence or presence of X-ray diffraction peak in Fig. 12, shows that the structure of products according to the present invention contains MgTiO 3 (○), partially containing ZnTiO 3 ) and CaTiO 3 () and, as other peaks, Mg 2 TiO 4 (▵ partially containing ZnTiO 4 ) and not containing MgO, CaO and TiO 2 . Fig. 13 shows a case not containing ZnO, which shows that the structure comprises MgTiO 3 (○) and CaTiO 3 (), also shows that MgO, CaO, TiO 2 are not contained. Further, although not illustrated, results of electron microscopic photographs show that the grain size increases along with elevation of the sintering temperature (1300°C : 3.1 µm, 1350 °C : 7.2 µm, 1400 °C : 12.8 µm, each measured by the Intercept method), pores decrease and densification is completed at 1400°C. The rupture cross section showed grain boundary destruction at 1300°C and intergrain destruction above 1350°C. Example 2 Using Ta 2 O 5 powder (99.9% purity) instead of the ZnO powder used in Example 1, a predetermined amount of the starting material (about 500 g in total) was weighed and mixed so as to provide a composition in which x and y vary in the formula: x MgTiO 3 ·(1-x)CaTiO 3 + y wt% Ta 2 O 5 in which y means % by weight of Ta 2 O 5 based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 ) as shown in Tables 2 and 3 and Figs. 14 and 17. Subsequently, molding products of the same shape were produced, sintered in the same manner, and then polished to prepare dielectric specimens of the same shape as in Example 1. Further, characteristics were measured by the same method and the results are shown in Tables 2-3 and Figs. 14-23. Further, as an example, results of X-ray diffraction of 0.93MgTiO 3 ·0.07CaTiO 3 3 wt% in a case of Ta 2 O 5 are shown in Fig. 24 (sintered at 1300 °C for 4 hours) and in Fig. 25 (sintered at 1350°C for 4 hours). From the foregoing results, the value Qu tends to decrease if x is small in x MgTiO 3 ·(1-x)CaTiO 3 but τf and ε r tend to increase toward the positive side. Further, the sintering density tends to increase along with elevation of [xMgTiO 3 ·(1-x)CaTiO 3 +3wt%Ta 2 O 5 ] ceramic composition No. x Amount of Ta 2 O 5 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0.940 3 1100 1400 4350 20.68 -12.48 3.870 2 0.9375 3 1100 1400 4310 20.82 -11.0 3.872 3 0.935 3 1100 1400 4260 20.97 - 8.50 3.875 4 0.930 3 1100 1400 4140 21.28 - 1.47 3.868 5 0.927 3 1100 1400 3940 21.50 1.02 3.875 6 0.923 3 1100 1400 3850 21.72 5.10 3.875 7 0.940 3 1100 1375 4380 20.76 -11.4 3.875 8 0.9375 3 1100 1375 4330 20.88 - 9.40 3.878 9 0.935 3 1100 1375 4260 21.07 - 6.58 3.881 10 0.930 3 1100 1375 4130 21.39 0.09 3.876 11 0.927 3 1100 1375 3890 21.60 1.70 3.884 12 0.923 3 1100 1375 3850 21.81 6.20 3.882 13 0.940 3 1100 1350 4230 20.77 -11.4 3.874 14 0.9375 3 1100 1350 4190 20.90 - 9.12 3.874 15 0.935 3 1100 1350 4180 21.08 - 6.40 3.881 16 0.930 3 1100 1350 4030 21.28 0.65 3.874 17 0.927 3 1100 1350 3920 21.64 2.26 3.884 18 0.923 3 1100 1350 3900 21.87 6.87 3.882 19 0.940 3 1100 1325 4230 20.49 -11.3 3.835 20 0.9375 3 1100 1325 4220 20.62 - 8.94 3.835 21 0.935 3 1100 1325 4190 20.90 - 5.78 3.850 22 0.930 3 1100 1325 4070 21.15 - 0.11 3.834 23 0.927 3 1100 1325 3980 21.46 3.09 3.855 24 0.923 3 1100 1325 3890 21.61 7.16 3.844 25 0.940 3 1100 1300 4130 19.06 -11.4 3.640 26 0.9375 3 1100 1300 4150 19.26 - 9.73 3.650 27 0.935 3 1100 1300 4180 19.71 - 6.75 3.687 28 0.930 3 1100 1300 4120 20.04 - 0.53 3.686 29 0.927 3 1100 1300 4070 20.70 1.82 3.753 30 0.923 3 1100 1300 3980 20.59 6.8 3.706 [xMgTiO 3 ·(1-x)CaTiO 3 +2∼4wt%Ta 2 O 5 ] ceramic composition No. x Amount of Ta 2 O 5 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0.923 3 1100 1425 3840 21.59 3.92 3.863 2 0.927 3 1100 1425 3900 21.34 0. 3.862 3 0.930 2 1100 1425 4060 21.26 0.31 3.848 4 0.930 4 1100 1425 4000 21.05 -6.27 3.872 5 0.930 2 1100 1400 4000 21.37 0.37 3.861 6 0.930 3 1100 1400 4140 21.28 -1.47 3.868 7 0.930 4 1100 1400 4000 21.25 -5.08 3.889 8 0.930 2 1100 1375 4000 21.44 0.81 3.863 9 0.930 3 1100 1375 4130 21.39 0.09 3.876 10 0.930 4 1100 1375 3960 21.31 -3.52 3.895 11 0.930 2 1100 1350 4050 21.47 1.10 3.865 12 0.930 3 1100 1350 4030 21.28 0.65 3.874 13 0.930 4 1100 1350 3980 21.36 -2.33 3.894 14 0.930 2 1100 1325 4100 21.23 0.42 3.829 15 0.930 3 1100 1325 4070 21.15 -0.11 3.834 16 0.930 4 1100 1325 4020 21.10 -0.76 3.848 17 0.930 2 1100 1300 4120 20.27 0.68 3.698 18 0.930 3 1100 1300 4120 20.04 -0.53 3.686 19 0.930 4 1100 1300 4020 19.90 -0.53 3.686 the sintering temperature but it becomes flat relative to the sintering temperature as the addition amount of Ta 2 O 5 increases. At a sintering temperature from 1300 to 1400°C, a preferred range of x is from 0.923 to 0.940, since practical characteristic ranges are shown for τf as -13 to +8 ppm/ °C, for ε r as 19 to 22 and for Qu as 3850 to 4380. Particularly, if x is 0.930 and the addition amount of Ta 2 O 5 is 3% by weight, at a sintering temperature, for example, of 1325 °C to 1375°C, τf is from -0.1 to +0.65 ppm/°C, ε r is from 21.1 to 21.4 and Qu is from 4030 to 4130, as shown in Fig. 14 to Fig. 19 and Tables 2 and 3, showing particularly excellent balance of the characteristics and the scattering thereof is extremely small. On the other hand, it is not preferred that CaTiO 3 is not contained, since the Qu value is large, ε r is small and, in addition, τf extremely decreases toward the negative side as -25 to -44 ppm/ °C. Further, the analysis method based on the absence or presence of X-ray diffraction peaks shown in Figs 24 and 25 shows that the structure of products according to the present invention contains MgTiO 3 (○) and CaTiO 3 () and MgTi 2 O 5 (▿) as other peaks and that MgO, CaO and TiO 2 are not contained. Further, although not illustrated, results of electron microscopic photographs show that the grain size increases along with the elevation of the sintering temperature (1300°C : 2.5 µm, 1350 °C : 3.7 µm, 1400 °C : 6.5 µm, each measured by the intercept method), pores decrease and densification is completed at 1350°C. The rupture cross-section shows grain boundary destruction at 1300 °C and intergrain destruction above 1350°C. Further, the surface tissue was classified into two kinds of grains, namely, huge grains (usual grains, 10-50 µm of grain size) and fine square grains (less than 1-10 µm). As a result of EDS (Energy Dispersive Spectrum) analysis, Mg, Ca, Ti and Si were detected from the usual grains while Mg, Ca, Ti and Ta were detected from the square grains. It is considered that the square grains are in the form of Ta compounds. Further, it is considered that the Si ingredient was mixed from the starting material. Example 3 Using Nb 2 O 5 powder (100% purity) instead of the ZnO powder used in Example 1, a predetermined amount of the starting material (about 500 g in total) was weighed and mixed so as to provide a composition in which x and y vary in the formula: xMgTiO 3 ·(1-x)CaTiO 3 + y wt% Nb 2 O 5 in which y means % by weight of Nb 2 O 5 based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 as shown in Tables 4-6 and Figs. 26-36. Table 4 shows the change of the addition amount of MgTiO 3 and Tables 5 and 6 show the change of the addition amount of Nb 2 O 5 . Subsequently, molding products of the same shape were produced, sintered in the same manner, and then polished to prepare dielectric specimens of the same shape as in Example 1 (Nos. 1-24 in Table 4 and Nos. 1-36 in Tables 5 and 6). Further, characteristics were measured by the same method and the results are shown in Tables 4-6 and Figs. 26-36. Further, as an example, results of X-ray diffraction of 0.93MgTiO 3 ·0.07CaTiO 3 are shown in Fig. 37 (containing 2%, 4% or 6% by weight of Nb 2 O 5 to 0.93MgTiO 3 · 0.07CaTiO 3 sintered at 1350 °C for 4 hours). From the foregoing results, the value Qu tends to decrease if x is small in xMgTiO 3 ·(1-x)CaTiO 3 but τf and ε r tend to increase toward the positive side. Further, the sintering density tends to increase along with elevation of the sintering temperature but it shows no substantial change to the change of the sintering temperature as the addition amount of Nb 2 O 5 increases. Further, although Qu and ε r do not change so much by the addition of Nb 2 O 5 , τf tends to decrease. Accordingly, addition of Nb 2 O 5 is suitable for controlling τf without reducing the performance of Qu and ε r . Further, if Nb 2 O 5 is not added, characteristics can not be measured when the sintering temperature is low (1275-1325 °C) (Table 6). Even upon sintering at 1350-1400°C, although characteristics can be measured τf is remarkably large (Table 5 and Fig. 31; 19.7 (No. 1) and 17.5 (No. 7), 15.1 ppm/°C (No. 13)). The sintering density is also low upon [xMgTiO 3 ·(1-x)CaTiO 3 +2wt%Nb 2 O 5 ] ceramic composition No. x Amount of Nb 2 O 5 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0.940 2 1100 1400 4380 20.77 -11.0 3.816 2 0.935 2 1100 1400 4250 21.08 - 6.50 3.821 3 0.930 2 1100 1400 4100 21.36 - 0.76 3.821 4 0.925 2 1100 1400 3930 21.71 4.95 3.824 5 0.940 2 1100 1375 4220 20.87 -10.8 3.828 6 0.935 2 1100 1375 4130 21.19 - 6.26 3.832 7 0.930 2 1100 1375 3980 21.48 - 0.16 3.830 8 0.925 2 1100 1375 3900 21.82 5.71 3.831 9 0.940 2 1100 1350 4230 20.92 -10.1 3.828 10 0.935 2 1100 1350 4150 21.23 - 5.55 3.834 11 0.930 2 1100 1350 4030 21.51 0.51 3.831 12 0.925 2 1100 1350 3920 21.86 8.01 3.834 13 0.940 2 1100 1325 4260 20.77 -11.0 3.805 14 0.935 2 1100 1325 4160 21.16 - 5.58 3.821 15 0.930 2 1100 1325 4050 21.44 0.52 3.817 16 0.925 2 1100 1325 3940 21.73 6.40 3.815 17 0.940 2 1100 1300 4540 20.07 -11.72 3.716 18 0.935 2 1100 1300 4320 20.73 - 6.21 3.757 19 0.930 2 1100 1300 4250 20.95 - 0.92 3.755 20 0.925 2 1100 1300 4160 21.15 7.49 3.739 21 0.940 2 1100 1275 4010 17.87 -13.0 3.444 22 0.935 2 1100 1275 4470 18.97 - 8.20 3.543 23 0.930 2 1100 1275 4320 19.05 - 3.69 3.532 24 0.925 2 1100 1275 4040 18.99 1.16 3.487 [0.93MgTiO 3 ·0.07CaTiO 3 +0∼6wt%Nb 2 O 5 ] ceramic composition No. Amount of Nb 2 O 5 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0 1100 1400 3490 21.78 19.7 3.834 2 1 1100 1400 2740 21.10 - 8.19 3.820 3 2 1100 1400 4100 21.36 - 0.76 3.821 4 3 1100 1400 4140 21.34 - 3.64 3.817 5 4 1100 1400 4170 21.33 - 7.27 3.819 6 6 1100 1400 4130 21.26 -11.6 3.812 7 0 1100 1375 3650 21.22 17.5 3.769 8 1 1100 1375 2260 21.16 - 7.63 3.823 9 2 1100 1375 3980 21.48 - 0.16 3.830 10 3 1100 1375 4120 21.55 - 2.47 3.829 11 4 1100 1375 4160 21.55 - 6.14 3.833 12 6 1100 1375 4110 21.52 - 9.93 3.830 13 0 1100 1350 3820 19.54 15.1 3.577 14 1 1100 1350 4190 21.49 1.71 3.829 15 2 1100 1350 4030 21.51 0.51 3.831 16 3 1100 1350 4120 21.55 - 1.57 3.833 17 4 1100 1350 4130 21.59 - 4.63 3.837 18 6 1100 1350 4110 21.56 - 9.00 3.837 [0.93MgTiO 3 ·0.07CaTiO 3 +0∼6wt%Nb 2 O 5 ] ceramic composition No. Amount of Nb 2 O 5 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 19 0 1100 1325 Unmeasurable 3.131 20 1 1100 1325 4250 21.25 0.53 3.799 21 2 1100 1325 4050 21.44 0.52 3.817 22 3 1100 1325 4140 21.49 - 2.04 3.816 23 4 1100 1325 4080 21.57 - 3.86 3.831 24 6 1100 1325 4040 21.58 - 8.16 3.829 25 0 1100 1300 Unmeasurable 26 1 1100 1300 4310 20.53 1.59 3.704 27 2 1100 1300 4250 20.95 - 0.92 3.755 28 3 1100 1300 4200 21.03 - 2.49 3.762 29 4 1100 1300 4070 21.34 - 3.18 3.792 30 6 1100 1300 4070 21.39 - 8.24 3.801 31 0 1100 1275 Unmeasurable 32 1 1100 1275 Unmeasurable 3.390 33 2 1100 1275 4320 19.05 - 3.69 3.532 34 3 1100 1275 3740 18.92 - 5.80 3.508 35 4 1100 1275 4230 19.97 - 4.93 3.621 36 6 1100 1275 4190 19.90 - 9.14 3.624 sintering at 1375 °C or 1350°C (No. 7 and No. 13 in Table 5) At a sintering temperature from 1300 to 1400°C and the addition amount of Nb 2 O 5 of 2% by weight, a preferred range of x is from 0.925 to 0.940, since practical characteristic ranges are shown for τf as -11.72 to +8.01 ppm/ °C, for ε r as 20.07 to 21.86 and for Qu as 3900 to 4540. Particularly, if x is 0.930 and the addition amount of Nb 2 O 5 is 2% by weight at a sintering temperature, for example, of 1350°C and 1375 °C, τf is -0.16 to +0.51 ppm/°C, ε r is 21.48 to 21.51 and Qu is 3980 to 4030, showing particularly excellent performance balance with scarce scattering thereof. Further, regarding τf, a small value around 0 ppm/ °C can be controlled easily since the variation coefficient to the sintering temperature is low. On the other hand, it is not preferred that CaTiO 3 is not contained, since the Qu value is large, but ε r is small and, in addition, τf extremely decreases toward the negative side as -25 to -44 ppm/ °C. Further, the analysis method based on the absence or presence of X-ray diffraction peaks in Fig. 37 shows that the structure of products according to the present invention contains MgTiO 3 (○)) and CaTiO 3 () and MgTi 2 O 5 (▵) as other peaks and that MgO, CaO and TiO 2 are not contained. Further, peaks for Nb 2 O 5 compounds were not detected. However, although the diffraction pattern is substantially the same for the addition amount of Nb 2 O 5 , peaks for MgTiO 3 and MgTi 2 O 5 shifted slightly to the lower angle side of 2 - along with increase of the addition amount from 2 to 6% by weight (Fig. 37). Accordingly, it is considered that Nb 5+ ions are solid solubilized in MgTiO 3 and MgTi 2 O 5 . Further, although not illustrated, results of electron microscopic photograph show that the grain size increases along with the elevation of the sintering temperature (1275°C : 2.6 µm, 1300 °C : 3.1 µm, 1350 °C : 4.9 µm and 1400°C : 6.1 µm, each measured by the intercept method), and pores decrease, showing that densification is completed at 1350 °C. The rupture cross-section shows inter-grain destruction for each of the cases. Example 4 Using MnO 2 powder (96% purity) instead of the ZnO powder used in Example 1, a predetermined amount of the starting material (about 500 g in total) was weighed and mixed so as to provide a composition in which x and y vary in the formula: xMgTiO 3 ·(1-x)CaTiO 3 + y wt% MnO 2 in which y means % by weight of MnO 2 based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 as shown in Tables 7-10 and Figs. 38 and 42. Table 7 shows the change of the addition amount (constitutional amount of CaTiO 3 and Tables 8-10 show the change of the addition amount of MnO 2 . Subsequently, molding products of the same shape were produced, sintered in the same manner, and then polished to prepare dielectric [xMgTiO 3 ·(1-x)CaTiO 3 ] ceramic composition(x=0.97∼0.93) No. 1-x Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0.03 1100 1425 4020 18.60 -49.6 3.765 2 0.05 1100 1425 2840 19.82 -33.8 3.803 3 0.07 1100 1425 2390 21.17 - 4.47 3.819 4 0.03 1100 1400 3800 18.58 -47.8 3.758 5 0.05 1100 1400 2900 19.79 -28.6 3.803 6 0.07 1100 1400 3490 21.78 19.72 3.834 7 0.03 1100 1375 4820 18.61 -33.3 3.716 8 0.05 1100 1375 4190 19.81 - 9.63 3.746 9 0.07 1100 1375 3650 21.22 17.5 3.769 10 0.03 1100 1350 4700 17.06 -34.4 3.529 11 0.05 1100 1350 4230 18.22 -11.7 3.543 12 0.07 1100 1350 3820 19.54 15.1 3.577 13 0.03 1100 1325 1150 13.56 -42.8 3.057 14 0.05 1100 1325 Unmeasurable 3.072 15 0.07 1100 1325 Unmeasurable 3.131 [0.94MgTiO 3 ·0.06CaTiO 3 +0∼6wt%MnO 2 ] ceramic composition No. Amount of MnO 2 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 3 1100 1425 3570 20.86 0.56 3.841 2 6 1100 1425 3090 20.68 - 2.38 3.854 3 3 1100 1400 3640 20.95 1.78 3.847 4 6 1100 1400 3080 20.79 - 1.21 3.861 5 3 1100 1375 3700 20.68 - 0.09 3.815 6 6 1100 1375 3080 20.84 0.20 3.862 7 3 1100 1350 3890 19.04 - 2.60 3.616 8 6 1100 1350 3150 20.45 - 1.23 3.807 9 3 1100 1325 660 17.00 - 3.26 3.384 10 6 1100 1325 3360 18.52 - 4.36 3.578 11 3 1100 1300 Unmeasurable 3.255 12 6 1100 1300 Unmeasurable 3.418 13 0 1100 1425 2480 20.46 -23.0 3.815 14 0 1100 1400 3360 20.51 -18.0 3.812 15 0 1100 1375 3940 20.83 4.84 3.778 16 0 1100 1350 3820 18.27 0.19 3.480 17 0 1100 1325 430 16.28 3.72 3.266 18 0 1100 1300 Unmeasurable 3.121 [0.95MgTiO 3 ·0.05CaTiO 3 +0.1∼0.6wt%MnO 2 ] ceramic composition No. Amount of MnO 2 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 0.1 1100 1400 3790 19.80 -31.4 3.804 2 0.2 1100 1400 3810 19.83 -31.3 3.807 3 0.3 1100 1400 3660 19.85 -30.7 3.814 4 0.6 1100 1400 3850 19.83 -29.6 3.818 5 0.1 1100 1375 3970 20.21 -11.8 3.805 6 0.2 1100 1375 4030 20.21 -10.7 3.804 7 0.3 1100 1375 4100 20.27 - 9.31 3.807 8 0.6 1100 1375 4060 20.25 - 9.87 3.810 9 0.1 1100 1350 4220 19.50 -10.4 3.713 10 0.2 1100 1350 4270 19.30 -10.7 3.693 11 0.3 1100 1350 4280 19.20 -11.6 3.683 12 0.6 1100 1350 4250 19.34 -11.1 3.703 13 0.1 1100 1325 3950 17.42 -13.4 3.449 14 0.2 1100 1325 3970 17.41 -12.7 3.462 1 5 0.3 1100 1325 3550 17.05 -14.2 3.422 16 0.6 1100 1325 3650 17.10 -14.1 3.426 17 0.1 1100 1300 1090 15.43 -26.4 3.230 18 0.2 1100 1300 1010 15.56 -30.2 3.251 19 0.3 1100 1300 1450 15.41 -21.5 3.232 20 0.6 1100 1300 950 15.54 -23.7 3.245 [0.93MgTiO 3 ·0.07CaTiO 3 +0∼6wt%MnO 2 ] ceramic composition No. Amount of MnO 2 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 3 1100 1425 3310 21.64 14.3 3.844 2 6 1100 1425 2900 21.38 12.8 3.855 3 3 1100 1400 3330 21.60 15.0 3.851 4 6 1100 1400 2880 21.42 12.3 3.864 5 3 1100 1375 3400 21.46 13.8 3.833 6 6 1100 1375 2890 21.44 11.8 3.865 7 3 1100 1350 3560 20.06 11.8 3.668 8 6 1100 1350 2960 21.00 12.0 3.803 9 3 1100 1325 1390 17.71 6.92 3.416 10 6 1100 1325 3140 18.90 7.07 3.563 11 3 1100 1300 Unmeasurable 3.268 12 6 1100 1300 Unmeasurable 3.395 13 0 1100 1425 2390 21.17 - 4.47 3.819 14 0 1100 1400 3490 21.78 19.7 3.834 15 0 1100 1375 3650 21.22 17.5 3.769 16 0 1100 1350 3820 19.54 15.1 3.577 17 0 1100 1325 Unmeasurable 3.131 specimens of the same shape as in Example 1 (Nos. 1-18 in Table 8, Nos. 1-20 in Table 9 and Nos. 1-17 in Table 10). Further, characteristics were measured by the same method. The results are shown in Tables 8-10 and Figs. 38-49. Further, as an example, results of X-ray diffraction of 0.94MgTiO 3 ·0.06CaTiO 3 are shown in Fig. 50 (containing 0%, 3% or 6% by weight of MnO 2 to 0.94MgTiO 3 ·0.06CaTiO 3 sintered at 1300 °C for 4 hours). From the foregoing results, the value Qu tends to decrease if (1-x) is large in xMgTiO 3 ·(1-x)CaTiO 3 , whereas τf and ε r tend to increase toward the positive side. Further, the sintering density tends to increase along with elevation of the sintering temperature but it shows no substantial change relative to the change of the sintering temperature as the addition amount of MnO 2 increases. Further, although ε r shows no substantial change, Qu and τf tend to decrease due to the addition of MnO 2 . Accordingly, addition of MnO 2 is suitable to the control of τf with no reduction of the performance of ε r . Further, as shown in Table 8, if MnO 2 is not added, the sintering density is small if the sintering temperature is low (1325 to 1350 °C) and a temperature higher than 1375°C is necessary for ensuring sufficient sinterability. On the other hand, when MnO 2 is added (3 to 6% by weight), sufficient sinterability is shown even at a sintering temperature of 1350°C. At a sintering temperature from 1350 to 1425°C and with the addition amount of MnO 2 of 3% by weight, a preferred range of (1-x) is from 0.06 to 0.07, since practical characteristic ranges are shown for τf as -2.60 to +15.0 ppm/°C, for ε r as 19.04 to 21.64 and for Qu as 3310 to 3890. Particularly, if (1-x) is 0.06 and the addition amount of MnO 2 is 3% by weight, at a sintering temperature, for example, of 1375 °C, τf is -0.09 ppm/ °C, ε r is 20.7 and Qu is 3700, showing particularly excellent balance of performance and the scattering thereof is extremely small. Further, regarding τf, since the variation coefficient to the sintering temperature is low, a small value around zero ppm/ °C can be controlled easily. On the other hand, it is not preferred that CaTiO 3 is not contained, since the Qu value is large, but ε r is small and, in addition, τf extremely decreases toward the negative side as -25 to -44 ppm/ °C. Further, the analysis method based on the absence or presence of X-ray diffraction peaks shown in Fig. 50 shows that the structure of products according to the present invention contains MgTiO 3 (○) and CaTiO 3 () and Mg 6 MnO 6 (▵) and Mn 3 O 4 (▿) as other peaks and that MgO, CaO and TiO 2 are not contained. Namely, the relative peak intensity of MgTiO 3 is reduced along with the increase of the addition amount of MnO 2 while Mg 6 MnO 8 , Mn 3 O 4 , etc. are increased. It is considered that Qu decreases due to the decrease in the amount of MgTiO 3 . Further, although not illustrated, results of electron microscopic photographs show that the grain size increases along with the elevation of the sintering temperature (1300°C : 2.7 µm, 1350 °C : 8.7 µm, 1400 °C: 9.2 µm, each measured by the intercept method). The rupture cross-section shows inter-grain destruction in each of the cases. As a result of EDS analysis, only Mg, Ca, Ti and Mn were detected. Example 5 Using Al 2 O 3 powder (99.9% purity) instead of the ZnO powder used in Example 1, a predetermined amount of the starting material (about 500 g in total) was weighed and mixed so as to provide a composition in which x and y vary in the formula: xMgTiO 3 ·(1-x)CaTiO 3 + y wt% Al 2 O 3 in which y means % by weight of Al 2 O 3 based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 as shown in Tables 7 and 11 and Figs. 51-58. Table 7 shows the change of the addition amount (constitutional amount) of CaTiO 3 (1-x) and Tables 11 shows the change of the addition amount of Al 2 O 3 . Subsequently, molding products of the same shape were produced, sintered in the same manner at a predetermined temperature and then polished to prepare dielectric specimens of the same shape as in Example 1 (Nos. 1-12 in Table 7 and Nos. 1-24 in Table 11). Further, characteristics were measured by the same method. The results are shown in Table 7 and 11 and Figs. [0.94MgTiO 3 ·0.06CaTiO 3 + 3∼12wt%Al 2 O 3 ] ceramic composition No. Amount of Al 2 O 3 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 12 1100 1425 4040 18.90 -13.2 3.725 2 9 1100 1400 3940 19.47 -11.3 3.756 3 12 1100 1400 4000 19.10 -13.2 3.739 4 3 1100 1375 3550 20.54 - 2.21 3.811 5 6 1100 1375 3530 20.07 - 3.85 3.781 6 9 1100 1375 3700 19.70 - 5.50 3.762 7 12 1100 1375 3860 19.34 - 5.77 3.739 8 3 1100 1350 3560 20.60 - 0.70 3.816 9 6 1100 1350 3390 20.13 - 0.74 3.781 10 9 1100 1350 3640 19.68 - 1.53 3.747 11 12 1100 1350 3750 19.09 - 2.06 3.698 12 3 1100 1325 3530 20.56 0.97 3.802 13 6 1100 1325 3360 20.00 1.91 3.759 14 9 1100 1325 3600 19.29 0 3.696 15 12 1100 1325 3850 18.20 - 1.99 3.593 16 3 1100 1300 3470 20.24 2.25 3.762 17 6 1100 1300 3370 19.50 2.59 3.695 18 9 1100 1300 3730 18.40 0.12 3.568 19 12 1100 1300 3870 16.39 - 5.22 3.376 20 3 1100 1275 3590 19.20 2.37 3.607 21 6 1100 1275 3470 18.05 1.76 3.517 22 9 1100 1275 2640 15.77 - 6.50 3.298 23 3 1100 1250 2870 16.18 - 2.39 3.287 24 6 1100 1250 2810 15.15 - 2.87 3.203 51-58. The resonance frequency used for the measurement of Qu is 5.7 to 6.3 GHz. Further, Fig. 59 shows the relation between the addition amount of Al 2 O 3 and the average grain size of the sintering product and Fig. 60 shows the relation between the sintering temperature and the average grain size of the sintering product. Further, as an example, Fig. 63 shows results of X-ray diffraction of 0.94MgTiO 3 .0.06CaTiO 3 .3-12 wt% Al 2 O 3 (sintered at 1350 °C for 4 hours). From the foregoing results, the value Qu tends to decrease if (1-x) is large in xMgTiO 3 ·(1-x)CaTiO 3 but τf and ε r tend to increase toward the positive side. Further, the sintering density tends to increase along with elevation of the sintering temperature. As the addition amount of Al 2 O 3 increases, Qu tends to increase, and ε r , τf and the sintering density tend to decrease. Then, at a sintering temperature of 1275 °C, Qu, ε r and the sintering density tend to decrease and their scattering is large, whereas highly stable performances are shown at 1300 to 1375°C. Further, when the addition amount of Al 2 O 3 is 3 to 9% by weight and the sintering temperature is 1300 to 1375 °C, well balanced performance and physical properties are shown, as Qu is 3360 to 3730, ε r is 18.4 to 20.6, τf is -2.2 to +2.6 ppm/ °C and the sintering density is 3.568 to 3.816 g/cm 3 as described above. In view of the above, appropriate addition of Al 2 O 3 can improve the performance of Qu while maintaining ε r and further it is suitable to the control of τf. Particularly, regarding τf, since the variation coefficient relative to the addition of Al 2 O 3 and the sintering temperature is low, a small value around 0 ppm/ °C can be controlled easily. Further, as shown in Fig. 60, the grain size of crystal grains increases along with the elevation of the sintering temperature (1300°C : 1.61 µm, 1350 °C : 2.19 µm, and 1400 °C : 4.46 µm, each measured by the intercept method), whereas the grain size decreased along with the increase of the addition amount of Al 2 O 3 as shown in Fig. 59 (3 wt% : 3.97, 6 wt% : 3.76, 12 wt% : 2.19). Further, Fig. 61 is a view explaining the structure of crystals by electron microscopic photograph (1000 magnification ratio) for a composition containing 6 wt% Al 2 O 3 added (sintered at 1350°C for 4 hours) and Fig. 62 shows a view explaining the structure of crystals by electron microscopic photograph (1000 magnification ratio) for a composition containing 12 wt% Al 2 O 3 added (sintered at 1350 °C for 4 hours). According to the figures, each of them shows substantially uniform grain size distribution. Further, rupture cross-section tissues show inter-grain destruction for each of 3-12 wt% Al 2 O 3 addition systems. Further, the analysis method based on the presence or absence of X-ray diffraction peak in Fig. 63 shows that the structure of products according to the present invention contains MgTiO 3 (○)) and CaTiO 3 () and MgTi 2 O 5 (▵) as other peaks and that reaction products with Al 2 O 3 are not contained. Example 6 Using Co 2 O 3 powder (99.1% purity) instead of the ZnO powder used in Example 1, a predetermined amount of the starting material (about 500 g in total) was weighed and mixed so as to provide a composition in which x and y vary in the formula: x MgTiO 3 ·(1-x)CaTiO 3 + y wt% Co 2 O 3 in which y means % by weight of Co 2 O 3 based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 as shown in Tables 7 and 12-13 and Figs. 64-71. Subsequently, molding products of the same shape were produced, sintered in the same manner, and then polished to prepare dielectric specimens of the same shape as in Example 1 (Nos. 1-12 in Table 7, Nos. 1-24 in Table 12 and Nos. 25 and 26 in Table 13). Further, characteristics were measured by the same method. The results are shown in Tables 7 and 12-13 and Figs. 64-71. Further, as an example, results of X-ray diffraction of 0.94MgTiO 3 .0.06CaTiO 3 .3wt%, 6wt% or 12 wt%Co 2 O 3 ceramic composition (sintered at 1300 °C for 4 hours) are shown in Fig. 73. From the foregoing results, the value Qu tends to decrease, whereas τf and ε r tend to increase towards the [0.94MgTiO 3 ·0.06CaTiO 3 +3∼12wt%Co 2 O 3 ] ceramic composition No. Amount of Co 2 O 3 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 1 3 1100 1450 3920 20.77 - 0.26 3.849 2 6 1100 1450 3780 20.58 - 0.40 3.851 3 9 1100 1450 3710 20.37 - 2.14 3.884 4 12 1100 1450 3640 20.17 - 0.99 3.893 5 3 1100 1425 3920 20.91 1.36 3.854 6 6 1100 1425 3840 20.72 - 0.74 3.878 7 9 1100 1425 3750 20.54 - 1.79 3.903 8 12 1100 1425 3680 20.32 - 3.29 3.921 9 3 1100 1400 3900 21.00 1.64 3.864 10 6 1100 1400 3840 20.78 - 0.05 3.889 11 9 1100 1400 3790 20.60 - 1.92 3.914 12 12 1100 1400 3700 20.43 - 3.13 3.935 13 3 1100 1375 4070 20.80 1.11 3.843 14 6 1100 1375 3870 20.82 - 0.10 3.894 15 9 1100 1375 3840 20.68 - 1.66 3.921 16 12 1100 1375 3740 20.49 - 2.26 3.943 17 3 1100 1350 4180 19.36 1.65 3.669 18 6 1100 1350 3970 20.35 - 0.03 3.832 19 9 1100 1350 3860 20.48 - 1.12 3.893 20 12 1100 1350 3760 20.46 - 1.87 3.934 21 3 1100 1325 2400 17.38 - 4.95 3.440 22 6 1100 1325 4160 18.38 - 3.02 3.596 23 9 1100 1325 4020 18.82 - 3.42 3.688 24 12 1100 1325 3860 19.34 - 3.02 3.792 [xMgTiO 3 ·(1-x)CaTiO 3 +6wt%Co 2 O 3 ] ceramic composition No. 1-x Amount of Co 2 O 3 (wt%) Calcining temp. (°C) Sinter. temp. (°C) Qu (6GHz) Rel. dielect. const. εr τf (ppm/°C) Sint. density (g/cm 3 ) 25 0.05 6 1100 1375 4100 20.10 -11.2 3.890 14 0.06 6 1100 1375 3870 20.82 - 0.10 3.894 26 0.07 6 1100 1375 3650 21.63 10.8 3.892 positive side if (1-x) is large in xMgTiO 3 ·(1-x)CaTiO 3 . Further, the sintering density tends to increase along with the elevation of the sintering temperature. Further, although ε r shows no substantial change Qu and τf tend to decrease and the sintering density tends to increase by the addition of Co 2 O 3 . Particularly, if (1-x) is 0.06 and the addition amount of Co 2 O 3 is 6% by weight, τf is -0.10 ppm/ °C, ε r is 20.82, Qu is 3870 and the sintering density is 3.894 at a sintering temperature, for example, of 1375°C, showing particularly excellent performance balance. Further, at a sintering temperature of 1350 to 1450 °C, each of Qu, ε r and τf scarcely scatters (for example, in case of Co 2 O 3 6 wt%, 3780 to 3970, 20.35 to 20.82, -0.03 to -0.74 ppm/ °C, respectively) and products of desired quality can be obtained stably. Further, even if the addition amount of Co 2 O 3 changed, each of Qu, ε r and τf scarcely scatters (for instance at a sintering temperature of 1400°C, 3700 to 3900, 20.43 to 21.00, -0.05 to -3.13 ppm/ °C, successively). Accordingly, even if the addition amount of Co 2 O 3 and the sintering temperature are changed, products of extremely stable quality can be obtained. Particularly, fine control for τf can be conducted extremely easily. Further, the analysis method based on the absence or presence of X-ray diffraction peaks in Fig. 73 shows that the structure of products according to the present invention contains MgTiO 3 (○) and CaTiO 3 (▪) and MgTi 2 O 4 () as other peaks and that reaction products with Co 2 O 3 are not contained. Further, the relative peak intensity of MgTiO 3 is reduced along with the increase of the addition amount of Co 2 O 3 while the intensity of MgTi 2 O 4 is increased. It is considered that Qu decreases due to the decrease in the amount of MgTiO 3 . Further, results of electron microscopic photographs (not illustrated) show that the grain size increases along with the elevation of the sintering temperature (1350°C : 4.30 µm, 1400 °C : 5.32 µm, 1450 °C : 7.20 µm, each measured by the intercept method) as showned in Table 72. The rupture cross-section tissue shows inter-grain destruction in each of the cases. The present invention is not restricted to specific embodiments described above but can be modified into various other embodiments depending on the purpose and the application within the scope of the invention. That is, the calcining conditions such as calcining temperature and sintering conditions such as sintering temperature can be selected variously. Further, also for the starting material for CaO, peroxides, hydroxides and nitrates and so on can also be used in addition to CaCO 3 described above. Also for other oxides, other compounds that can form oxides by heating may also be used.

Claims: A microwave dielectric ceramic composition comprising, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTiO 3 (0.925) ≦x ≦0.950) , to which 3 to 9 parts by weight of ZnO is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . A microwave dielectric ceramic composition as defined in claim 1, which has a Qu value in the range of 3530 to 4370 (at 6 Ghz), a temperature coefficient of the resonance frequency (τf) in the range of -14.7 to +21.9 ppm/°C and relative dielectric constant in the range of 19 to 22. A microwave dielectric ceramic composition comprising, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTiO 3 (0.923 ≦x ≦0.950) , to which 2 to 4 parts by weight of Ta 2 O 5 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . A microwave dielectric ceramic composition as defined in claim 3, wherein x is within a range of 0.923 to 0.940. A microwave dielectric ceramic composition as defined in claim 3, which has a Qu value in the range of 3840 to 4380 (at 6 Ghz), a temperature coefficient of the resonance frequency (τf) in the range of -12.5 to +7.2 ppm/°C and relative dielectric constant in the range of 19.1 to 21.9. A microwave dielectric ceramic composition comprising, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTiO 3 (0.925 ≦x ≦0.940) , to which 1 to 6 parts by weight of Nb 2 O 5 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . A microwave dielectric ceramic composition as defined in claim 6, wherein the addition amount of Nb 2 O 5 is 1 to 4 parts by weight. A microwave dielectric ceramic composition as defined in claim 6, which has a Qu value in the range of 3900 to 4540 (at 6 Ghz), a temperature coefficient of the resonance frequency (τf) in the range of -13.0 to + 8.01 ppm/°C and relative dielectric constant in the range of 18.97 to 21.86. A microwave dielectric ceramic composition comprising, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTiO 3 (0.93≦ x ≦0.95) , to which 0.1 to 6 parts by weight of is added and incorporated MnO 2 based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . A microwave dielectric ceramic composition as defined in claim 9, wherein the addition amount of MnO 2 is 3 to 6 parts by weight. A microwave dielectric ceramic composition as defined in claim 9 or 10, which has a Qu value in the range of 2880 to 3890 (at 6 Ghz), a temperature coefficient of the resonance frequency (τf) in the range of -4.4 to +15.0 ppm/°C and relative dielectric constant in the range of 19 to 21. A microwave dielectric ceramic composition comprising, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTio 3 (0.93≦x ≦0.95) , to which 3 to 12 parts by weight of A1 2 O 3 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . A microwave dielectric ceramic composition as defined in claim 12, wherein the addition amount of A1 2 O 3 is 3 to 9 parts by weight. A microwave dielectric ceramic composition as defined in claim 12, which has a Qu value in the range of 3360 to 3730 (at 6 Ghz), a temperature coefficient of the resonance (τf) in the range of -2.2 to + 2.6 ppm/°C and relative dielectric constant in the range of 18.4 to 20.6. A microwave dielectric ceramic composition comprising, as the main ingredient, a composition represented by xMgTiO 3 ·(1-x)CaTiO 3 (0.93≦x ≦0.95) , to which 3 to 12 parts by weight of Co 2 O 3 is added and incorporated based on 100 parts by weight of xMgTiO 3 ·(1-x)CaTiO 3 . A microwave dielectric ceramic composition as defined in claim 15, wherein the addition amount of Co 2 O 3 is 3 to 9 parts by weight. A microwave dielectric ceramic composition as defined in claim 15, which has a Qu value in the range of 3640 to 4180 (at 6 Ghz), a temperature coefficient of the resonance frequency (τf) in the range of -11.2 to +10.8 ppm/°C and relative dielectric constant in the range of 17.4 to 21.0.

Inventors: KATOH TOKIOMI, OZEKI HIROFUMI, KATOH, TOKIOMI, OZEKI, HIROFUMI, Katoh, Tokiomi, c/o NGK SPARK PLUG CO., LTD., OZEKI, HIROFUMI, C/O NGK SPARK PLUG CO., LTD.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD
Application year: 1993
Main classification: C04B35
IPC codes: C04B35, H01P7