Dielectric ceramic compositions and dielectric resonators

Abstract: The present invention provides dielectric ceramics with less variation of temperature coefficient at a resonant frequency due to heating history during the sintering of ZrTiO₄ and ZrO₂ - SnO₂ - TiO₂ ceramics, and having a high unloaded Q value and a high dielectric constant, and a temperature coefficient at a resonant frequency which is widely variable as desired, and dielectric resonators using the dielectric ceramics which have a high unloaded Q value and a strong electrode layer. The main components of the dielectric ceramics (2) and (5) may be expressed by the formula: xZrO₂ - yTiO₂ - zA (1+u)/3 B (2-u)/3 O₂ wherein A denotes at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, B denotes at least one component selected from the group (B) consisting of Nb and Ta, and x, y, z and u (x, y and z are molar fractions and u is a value within the range from 0 to 1.90) have the relation of x + y + z = 1.0 , 0.10 ≦ x ≦ 0.60, 0.20 ≦ y ≦ 0.60, 0.01 ≦ z ≦ 0.70. The main component may include, as accessory components, at least one component selected from the group (C) consisting of Ba, Sr, Ca, Cu, Bi and W at 0.005 to 7.000 % by weight of the entire weight of the ceramic. According to the cylindrical coaxial dielectric resonator, electromagnetic waves are incident in the direction of an opening end (3) and a necessary output is obtained from electrodes (1) and (4) by using the TEM mode.

Description: This invention relates to dielectric resonators and dielectric ceramics for use in such high-frequency ranges as microwave and millimeter-wave frequencies. Recently, dielectric ceramics have been widely used in dielectric resonators and filters in microwave and millimeter-wave frequencies at wavelengths of several centimeters or less (hereinafter referred to as microwave in general). It is required that a dielectric material for use in such applications have a high unloaded Q (Qu) value and dielectric constant ε r ' and that the temperature coefficient at a resonant frequency τ f be variable as desired. The Q value is the inverse of an inductive loss tan δ. Various materials appropriate for use in such applications have been conventionally reported, among which ZrTiO 4 ceramics are included. Also included in such materials are ZrO 2 -SnO 2 -TiO 2 ceramics, the ZrO 2 -SnO 2 -TiO 2 -MgO ceramic suggested in Japanese Laid-Open Patent No. 62-132769 and the ZrO 2 -SnO 2 -TiO 2 -CoO-Nb 2 O 5 ceramic in Japanese Laid-Open Patent No. 2-192460, for example. However, although the ZrTiO 4 ceramics according to the prior art have a high dielectric constant of 45, the temperature coefficient at a resonant frequency is high in the positive side at 54ppm/°C, and the temperature coefficient at a resonant frequency is significantly varied by the heating history during sintering. The ZrO 2 -SnO 2 -TiO 2 ceramic has achieved a low temperature coefficient of about 0ppm/°C at a resonant frequency, but the variation of temperature coefficient at the resonant frequency caused by the heating history causes problems. In addition, conventional materials have such problems that the dielectric constant and unloaded Q value are low, and that the temperature coefficient at a resonant frequency cannot be varied as desired. Further, in the case of application to a coaxial resonator having electrodes formed on the surface of the dielectric ceramic, a planar filter and the like, there are problems in that the resonant frequency is easily deviated and the unloaded Q value is decreased when the bond strength of the electrode layer to the dielectric ceramic is low. In EP-A-587 140 a dielectric ceramic and a TE01δ-mode dielectric resonator including the dielectric ceramic is disclosed. The dielectric ceramic is placed in a metal cavity and the dielectric resonator utilizing TE01δ-mode resonance of the dielectric by electromagnetic wave emitted from an antenna is placed in a side surface of the cavity. Thereby the TE01δ-mode dielectric resonator has got a high unloaded Q value and a compact size. In DE-A-39 15 339 a dielectric ceramic is disclosed having a high dielectric constant and a relatively low dependence on temperature of the dielectric constant within +/-15% over a temperature range of -55°C to +125°C comprising a mixture of bariumtitanate and a solid solution of bariumtitanate of the perovskite type including at least a compound of niobium oxide and tantalum oxide and at least a compound of cobalt oxide, nickel oxide, manganese oxid, copper oxide and rare-earth elements oxides. The object of the present invention is to provide dielectric resonators which comprise strong electrode layers having a high unloaded Q value. It is another object of the present invention to provide a dielectric resonator providing ZrTiO 4 and ZrO 2 -SnO 2 -TiO 2 ceramics with less variation of temperature coefficient at a resonant frequency due to heating history during sintering. It is still another object of the present invention to provide a dielectric resonator providing dielectric ceramics that have a high unloaded Q value and a high dielectric constant, and have a temperature coefficient at a resonant frequency which is variable as desired. The subject of the present invention is to achieve one of these objects or to achieve more than two objects at the same time. In order to achieve the objects described above, the present invention provides a dielectric resonator comprising the dielectric ceramic comprising as the main component a complex oxide formed of both Zr and Ti, at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta, and as the accessory components at least one component selected from the group (C) consisting of Ba, Sr, Ca, Cu, Bi and W, wherein the main component of the dielectric ceramic is expressed by the Formula: xZrO 2 - yTiO 2 - zA (1+u)/3 B (2-u)/3 O 2 , wherein A denotes at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, B denotes at least one component selected from the group (B) consisting of Nb and Ta, and x, y, z and u are present within the range expressed by Formula 1, wherein x, y and z denote molar fractions and u denotes a value expressed by the Formula 1. x + y + z = 1 0.10 ≦ x ≦ 0.60 0.20 ≦ y ≦ 0.60 0.01 ≦ z ≦ 0.70 0 ≦ u ≦ 1.90 and wherein the accessory components of the dielectric ceramic are present within the range of 0.005 to 7.000 % by weight based on the entire weight of the ceramic, characterized in that the dielectric resonator is a cylindrical coaxial dielectric resonator, in which copper (Cu) is coated on to the surface of the cylindrical dielectric ceramic (2) so to form copper electrodes and so that the electrodes are not formed on the surface of an opening end (3), wherein electromagnetic waves are incident in the direction of the opening end (3), and the resonance (TEM mode) of the electromagnetic waves in a specific frequency area is utilized to obtain the necessary output from the electrodes (1,4). For the present dielectric resonator it is preferred that the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta. Preferably, the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta, and a/b (a and b denote the total of molar fractions of the components A and B) ranges from 0.5 to 1.9. For the present dielectric resonator, it is preferred that the main component further comprises a complex oxide formed of at least one component selected from the group (D) consisting of Sn, Hf and Ge. Preferably, the main component of the dielectric ceramic of the dielectric resonator is expressed by the Formula: xZrO 2 - yTiO 2 - zA (1+u)/3 B (2-u)/3 O 2 - vDO 2 , wherein A denotes at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, B denotes at least one component selected from the group (B) consisting of Nb and Ta, and D denotes at least one component selected from the group (D) consisting of Sn, Hf and Ge, and x, y, z, v, and u are present within the range expressed by Formula 2, wherein x, y, z and v denote molar fractions and u denotes a value expressed by the Formula 2. x + y + z + v = 1 0.10 ≦ x ≦ 0.60 0.20 ≦ y ≦ 0.60 0.01 ≦ z ≦ 0.50 0.001 ≦ v ≦ 0.20 0 ≦ u ≦ 1.90 Further, it is preferred that the accessory components of the dielectric ceramic of the dielectric resonator comprise at least one component selected from the group (C) consisting of Ba, Sr, Ca, Cu, Bi and W within the range from 0.005 to 7.000 % by weight based on the entire weight of the ceramic. For the present dielectric resonator, it is preferred that the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, at least one component selected from the group (B) consisting of Nb and Ta, and at least one component selected from the group (D) consisting of Sn, Hf and Ge. Preferably, the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, at least one component selected from the group (B) consisting of Nb and Ta, and at least one component selected from the group (D) consisting of Sn, Hf and Ge, and a/b (a and b denote the total of molar fractions of the components A and B) ranges from 0.5 to 1.9. In the structure of the present invention, the main component includes a complex oxide formed of both Zr and Ti, at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta, and as the accessory components at least one component selected from the group (C) consisting of Ba, Sr, Ca, Cu, Bi and W. Consequently, the present invention provides dielectric ceramics with less variation of temperature coefficient at a resonant frequency due to heating history during the sintering of the ZrTiO 4 ceramic. According to the preferred structure of the composition formula and the Formula 1, the present invention provides dielectric resonators that have a high unloaded Q value and a high dielectric constant, and have a temperature coefficient at a resonant frequency which is variable as desired. According to the dielectric resonator comprising the dielectric ceramic expressed by the composition formula and the Formula 1, the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta. Thus, the present invention provides dielectric resonators comprising dielectric ceramics having a higher unloaded Q value and a high dielectric constant, and is superior in thermo-stability at a resonant frequency. According to the dielectric resonator comprising the dielectric ceramic expressed by the composition formula and the Formula 1, the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta, and a/b (a and b denote the total of molar fractions of the components A and B) ranges from 0.5 to 1.9. Thus, the present invention provides dielectric resonators comprising dielectric ceramics having a much higher unloaded Q value and a high dielectric constant, and is superior in thermo-stability at a resonant frequency. For the present dielectric resonators, it is preferred that the main component further comprises a complex oxide formed of at least one component selected from the group (D) consisting of Sn, Hf and Ge. Thus, the present invention provides dielectric resonators with less variation of temperature coefficient at a resonant frequency due to heating history during the sintering of ZrO 2 - SnO 2 - TiO 2 ceramics. For the present dielectric resonator comprising the dielectric ceramic expressed by the composition formula and the Formula 2, it is preferred that the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, at least one component selected from the group (B) consisting of Nb and Ta, and at least one component selected from the group (D) consisting of Sn, Hf and Ge. Thus, the present invention provides dielectric resonators comprising dielectric ceramics having a higher unloaded Q value and a high dielectric constant, and is superior in thermo-stability at a resonant frequency. According to the dielectric resonator comprising the dielectric ceramic expressed by the composition formula and the Formula 2, the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, at least one component selected from the group (B) consisting of Nb and Ta, and at least one component selected from the group (D) consisting of Sn, Hf and Ge, and a/b (a and b denote the total of molar fractions of the components A and B) ranges from 0.5 to 1.9. Thus, the present invention provides dielectric resonators comprising dielectric ceramics having a much higher unloaded Q value and a high dielectric constant, and is superior in thermo-stability at a resonant frequency. The dielectric resonator of the present invention has a high unloaded Q value and a strong electrode layer. In the foregoing, the ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component of each of the groups A, B and D is a phase in which both or either of Zr and Ti sites are (is) substituted with at least one component of each of the groups A, B and D. Basically, the ZrTiO 4 phase has an element ratio Zr/Ti = 1. Actually, also in a composition area where the element ratio is slightly shifted to the direction which is higher or lower than 1 (for example, in case Zr and Ti are soluble in the ZrTiO 4 phase), an area which can be regarded as the ZrTiO 4 constitution is present. Such an area is crystallographically referred to as a ZrTiO 4 phase. Fig. 1A is a sectional view of a cylindrical coaxial dielectric resonator, which is axially cut off, according to an embodiment of the present invention. Fig. 1B is a sectional view taken out along the line I-I shown in Fig. 1A. Any compound such as oxide, carbonate, hydroxide, chloride , alkoxide of the component elements described above may be used as an initial material of the dielectric ceramic of the dielectric resonator according to the present invention. As blending methods of powdery raw materials, wet blending for mixing the materials with water or organic solvent in a ball mill and dry blending for mixing them by a mixer or a ball mill, etc. without using any solvent are generally known and any of these methods may be employed. Alternatively, the alkoxide method and coprecipitation method may be used depending on the initial materials. Because the process is thus comparatively uncomplicated, and a homogeneous mixture can be easily obtained, it is desirable to employ the wet blending method for mixing them in a ball mill by using a solvent, and a dispersing agent may be additionally used for increasing the dispersing property of powders, or pH adjustment may be performed. Although calcination of the mixture is not required, the sintering time can be reduced by calcination. Although the calcination temperature depends on the particular compositions, it is generally in the order of 1 to 8 hrs at about 700 to 1200°C. As the milling method for the calcined material or mixture, any suitable method such as using a ball mill, high-speed rotor mill, media agitating mill and jet mill may be employed. For molding, press molding is generally carried out to obtain a desired shape. Although not specifically limited, the pressure used in the press molding is generally in a range of approximately 0.5 to 2 tone/cm 2 . A binder used for molding may be a binder used for molding ceramics, such as a polyvinyl alcohol binder, a polyvinyl butylal binder, an acrylic resin binder or a wax binder. Although not specifically limited, the amount of the binder to be used is generally in a range of approximately 0.5 to 1 % by weight by solid matter conversion. Although sintering is not specifically limited, as it depends on the particular compositions and dimensions of the moldings, it is generally desirable to perform firing at a temperature of approximately 400 to 700°C for about 1 to 24 hrs in order to remove binders, and then, at approximately 1100 to 1650°C for about 2 to 100 hrs. An example of a cylindrical coaxial dielectric resonator will be described with reference to the drawings. Fig. 1A is a sectional view of the cylindrical coaxial dielectric resonator which is axially cut off, in which electrodes 1 and 4 are continuously formed on the surface of a cylindrical dielectric ceramic 2. The electrode is not formed on the surface of an opening end 3. Fig. 1B is a sectional view taken along the line I-I shown in Fig. 1A. According to the cylindrical coaxial dielectric resonator, electromagnetic waves are incident in the direction of the opening end 3, and the resonance (TEM mode) of the electromagnetic waves in a specific frequency area is utilized to obtain the necessary output from the electrodes 1 and 4. The present invention will be described with reference to the following examples. Example 1 As initial materials, ZrO 2 , TiO 2 , MgO, CoO, ZnO, NiO, Nb 2 O 5 , Ta 2 O 5 , MnCO 3 , BaCO 3 , SrCO 3 , CaCO 3 , CuO, Bi 2 O 3 , WO 3 , SnO 2 , HfO 2 and GeO 2 of high chemical purity (more than 98wt.%) were used, weighed so as to make predetermined compositions and wet-blended with ethanol by using a ball mill. The volume ratio between the powder and ethanol was approximately 2:3. The mixture was removed from the ball mill, dried, and calcined for 2 hrs at 1000°C in the air. The calcined product was wet-milled in the ball mill with ethanol. After the milled slurry was removed from the ball mill and dried, the powder was mixed with 8 % by weight of polyvinyl alcohol solution of 6 vol.% in concentration as a binder, homogenized, and granulated by sieving through a 32 mesh screen. The granulated powder was molded into a disk of 7 mm in diameter and approximately 3 mm in thickness by using molds and an oil hydraulic press at a molding pressure of 1.3 ton/cm 2 . The molding was placed in a magnesia vessel of high purity, kept in the air at a temperature of 600°C for 4 hrs to remove binders, then retained in the air at 1200 to 1500°C for 24 hrs for sintering, and quenched (taken out of a furnace and air-cooled) or slowly cooled down to 1000°C (at a cooling rate of 20°C /hr) thereafter, and dielectric ceramics were obtained. The resonant frequency was obtained from measurement by the dielectric rod resonator method. The temperature coefficient at a resonant frequency τ f was obtained in a range between -25°C and 85°C. The compositions of main components and the amount of accessory components, which are to be added, of the dielectric ceramics thus produced are shown in Tables 1 and 2, respectively. The amount of the accessory component is the weight of an oxide form in which the component is present in the ceramic, and is a value which is changed into {BaO, SrO, CaO, CuO, Bi 2 O 3 , WO 3 } Cooling conditions after sintering and a temperature coefficient at a resonant frequency (ppm/°C) are shown in Table 3. In Tables 1 to 3, comparative examples have an asterisk. Sample Composition (molar fraction) No. Zr Ti Mg Co Zn Ni Mn Nb Ta Sn Hf Ge *1,*2 0.50 0.50 0 0 0 0 0 0 0 0 0 0 3,4 0.35 0.50 0.05 0 0 0 0 0.10 0 0 0 0 5,6 0.35 0.50 0 0.05 0 0 0 0.10 0 0 0 0 7.8 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.10 0 0 0 0 9,10 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.10 0 0 0 0 11,12 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.10 0 0 0 0 13,14 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.05 0.05 0 0 0 *15*16 0.40 0.50 0 0 0 0 0 0 0 0.10 0 0 *17*18 0.32 0.50 0 0.03 0 0 0 0.05 0 0.10 0 0 19,20 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.05 0.05 0.01 0 0 21,22 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.05 0.05 0 0.01 0 23,24 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.05 0.05 0 0 0.01 25,26 0.35 0.50 0.01 0.01 0.01 0.01 0.01 0.05 0.05 0.01 0.01 0.01 Sample No. Amount of additive (wt.%) Ba Sr Ca Cu Bi W *1,*2 0 0.1 0 0 0 0 3,4 0 0.1 0 0 0 0 5,6 0.1 0 0 0 0 0 7,8 0 0 0 0 0.1 0 9,10 0 0 0 0.1 0 0 11,12 0 0 0 0 0 0.1 13,14 0.1 0.1 0.1 0.1 0 0 *15*16 0 0 0 0 0 0 *17*18 0 0 0 0 0 0 19,20 0.1 0.1 0.1 0.1 0 0 21,22 0.1 0 0 0 0 0 23,24 0 0.1 0 0 0 0 25,26 0.1 0.1 0.1 0.1 0 0 Sample No. Cooling condition after sintering τ f (ppm/°C) *1 Quenching 58.9 *2 Slow cooling 69.1 3 Quenching 8.2 4 Slow cooling 8.9 5 Quenching 5.5 6 Slow cooling 4.8 7 Quenching 9.4 8 Slow cooling 9.3 9 Quenching 9.7 10 Slow cooling 10.1 11 Quenching 9.8 12 Slow cooling 9.6 13 Quenching 9.8 14 Slow cooling 9.7 *15 Quenching -5.7 *16 Slow cooling 1.2 *17 Quenching -22.5 *18 Slow cooling -16.3 19 Quenching 5.8 20 Slow cooling 4.2 21 Quenching 0.9 22 Slow cooling 1.2 23 Quenching 9.5 24 Slow cooling 9.9 25 Quenching 8.5 26 Slow cooling 9.7 As recognized from the results shown in Table 3, in dielectric resonators comprising dielectric ceramics of sample Nos. 3 to 14 and 19 to 26 of the present example, the variation of temperature coefficient at a resonant frequency due to the heating history during sintering of ZrTiO 4 and ZrO 2 -SnO 2 -TiO 2 ceramics is reduced. Example 2 As initial materials, ZrO 2 , TiO 2 , MgO, CoO, ZnO, NiO, MnCO 3 , Nb 2 O 5 , Ta 2 O 5 , BaCO 3 , SrCO 3 , CaCO 3 , CuO, Bi 2 O 3 , and WO 3 of high chemical purity which are the same as in Example 1 were used, weighed so as to make a predetermined compositions and wet-blended with ethanol by using a ball mill. The volume ratio between the powder and ethanol was approximately 2:3. The mixture was removed from the ball mill, dried, and calcined for 2 to 8 hrs at 800 to 1250°C in the air. The calcined product was wet-milled in the ball mill with ethanol. After the milled slurry was removed from the ball mill and dried, the powder was mixed with 8 % by weight of polyvinyl alcohol solution of 6 vol.% in concentration added thereto as a binder, homogenized, and granulated by sieving through 32 mesh screen. The granulated powder was molded into a disk of 7 mm in diameter and approximately 3 mm in thickness by using molds and an oil hydraulic press at a molding pressure of 1.3 ton/cm 2 . The molding was placed in a magnesia vessel of high purity, kept in the air at a temperature of 400 to 700°C for 4 to 8 hrs to remove binders, retained in the air at 1200°C to 1650°C for 1 to 100 hrs for sintering, and dielectric ceramics were obtained. The resonant frequency. unloaded Q (Qu) value and dielectric constant ε r were obtained from measurement by the dielectric rod resonator method. The temperature coefficient at a resonant frequency τ f was obtained in a range between -25°C and 85°C. The resonant frequency was obtained in a range between 4GHz and 12GHz. The compositions of main components and the amount of accessory components, which are to be added, of the dielectric ceramics thus produced are shown in Table 4. The dielectric constant thus obtained, the temperature at a resonant frequency τ f (ppm/°C) and the unloaded Q value are shown in Table 5. In Tables 4 and 5, comparative examples have an asterisk. Sample No. A B Composition of main component Accessory (molar fraction) (value) component (wt.%) x y z u *27 Mg Nb 0.400 0.150 0.450 0 Sr 0.005 *28 Co Nb 0.400 0.150 0.450 0 Sr 0.005 *29 Zn Nb 0.400 0.150 0.450 0 Ba 0.005 *30 Ni Nb 0.400 0.150 0.450 0 Ca 0.005 31 Mg Nb 0.200 0.200 0.600 0 Sr 1.000 32 Co Nb 0.200 0.200 0.600 0 Sr 1.000 33 Ni Nb 0.200 0.200 0.600 0 Sr 1.000 34 Mg Nb 0.450 0.200 0.350 0 Sr 0.500 35 Co Nb 0.450 0.200 0.350 0 Sr 0.500 36 Mg Nb 0.200 0.600 0.200 0 Ba 0.500 37 Zn Nb 0.200 0.600 0.200 0 Ba 0.500 *38 Mg Nb 0.150 0.700 0.150 0 Sr 1.000 *39 Mg Nb 0.150 0.120 0.730 0 Ba 0.500 40 Mg Nb 0.100 0.200 0.700 0 Ba 0.500 41 Ni Nb 0.100 0.200 0.700 0 Ba 0.500 *42 - - 0.550 0.450 0 0 - 0 43 Mg Nb 0.490 0.500 0.010 0 Ba 0.005 44 Co Nb 0.490 0.500 0.010 0 Ba 0.005 45 Zn Nb 0.490 0.500 0.010 0 Ba 0.005 46 Ni Nb 0.490 0.500 0.010 0 Ba 0.005 47 Mg Nb 0.300 0.300 0.400 0 Sr 1.000 48 Mg Nb 0.400 0.400 0.200 0 Sr 0.005 49 Co Nb 0.400 0.400 0.200 0 Sr 0.005 50 Zn Nb 0.400 0.400 0.200 0 Sr 0.005 51 Mg Nb 0.340 0.520 0.140 0 Sr 0.100 52 Co Nb 0.340 0.520 0.140 0 Sr 0.100 53 Zn Nb 0.340 0.520 0.140 0 Sr 0.100 54 Ni Nb 0.340 0.520 0.140 0 Sr 0.100 55 Mg Nb 0.450 0.450 0.100 0 Sr 0.100 *56 Mg Nb 0.650 0.200 0.100 0 Ca 0.100 *57 Co Nb 0.650 0.200 0.100 0 Ca 0.100 58 Mg Nb 0.600 0.300 0.100 0 Ca 0.100 59 Mg Nb 0.100 0.400 0.500 0 Bi 0.100 60 Ni Nb 0.100 0.400 0.500 0 Bi 0.100 *61 Mg Nb 0.050 0.500 0.450 0 Ca 0.100 *62 Co Nb 0.050 0.500 0.450 0 Bi 0.100 63 Mg Nb 0.450 0.350 0.200 0 Sr 1.000 64 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 Cu 0.005 65 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 Cu 0.100 66 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 0.005 67 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 0.100 68 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 1.000 69 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 2.000 70 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 71 Mg Nb 0.350 0.450 0.200 0.01 Sr 1.000 72 Co Nb 0.350 0.450 0.200 0.01 Sr 1.000 73 Zn Nb 0.350 0.450 0.200 0.01 Sr 1.000 74 Ni Nb 0.350 0.450 0.200 0.01 Sr 1.000 75 Mg Nb 0.350 0.450 0.200 0.05 Sr 1.000 76 Mg Nb 0.350 0.450 0.200 0.20 Sr 1.000 77 Co Nb 0.350 0.450 0.200 0.20 Sr 1.000 78 Mg Nb 0.350 0.450 0.200 0.50 Sr 1.000 79 Mg Nb 0.350 0.450 0.200 1.00 Sr 1.000 80 Mg Nb 0.350 0.450 0.200 1.90 Sr 1.000 81 Co Nb 0.350 0.450 0.200 1.90 Sr 1.000 82 Mg Nb 0.350 0.450 0.200 2.00 Sr 1.000 83 Mg 1/4 Co 1/4 Nb 0.340 0.520 0.140 0 Sr 0.100 Zn 1/4 Ni 1/4 84 Mg 1/2 Co 1/2 Nb 0.340 0.520 0.140 1.00 Sr 0.100 85 Mg 1/3 Co 1/3 Ta 0.340 0.520 0.140 1.00 Sr 0.100 Ni 1/3 86 Mg 1/4 Co 1/4 Nb 1/2 0.340 0.520 0.140 1.00 Sr 0.100 Zn 1/4 Ni 1/4 Ta 1/2 87 Mg 39/40 Nb 1/2 0.340 0.520 0.140 0.02 Bi 0.100 Mn 1/40 Ta 1/2 88 Mg 113/200 Nb 0.328 0.502 0.170 0.41 Bi 0.100 Mn 87/200 89 Mn Nb 0.200 0.600 0.200 0 Ca 0.100 90 Mg Nb 0.300 0.400 0.300 1.00 Sr 0.500 91 Mg Nb 0.300 0.400 0.300 1.00 Ba 0.500 92 Mg Nb 0.300 0.400 0.300 1.00 Ca 0.500 93 Mg Nb 0.300 0.400 0.300 1.00 Bi 0.500 94 Mg Nb 0.300 0.400 0.300 1.00 Ba 0.500 Sr 0.500 Ca 0.500 Bi 0.500 95 Mg Nb 0.300 0.400 0.300 1.00 Sr 1.500 96 Mg Nb 0.300 0.400 0.300 1.00 Sr 3.000 97 Mg Nb 0.300 0.400 0.300 1.00 Sr 7.000 *98 Mg Nb 0.300 0.400 0.300 1.00 Sr 8.000 Sample No. ε r τ f Qu *27 30.1 -84.9 950 *28 29.9 -70.5 850 *29 30.0 -88.7 970 *30 30.8 -69.4 830 31 32.5 -10.8 8000 32 31.3 -8.9 9000 33 30.9 -7.8 8100 34 32.3 -32.1 4300 35 33.1 -19.5 4800 36 57.5 47.4 5300 37 55.5 40.2 6100 *38 75.8 225.2 370 *39 28.0 -84.8 980 40 33.8 -8.5 9600 41 26.8 -5.4 9600 *42 45.8 250.8 1800 43 44.5 42.3 3900 44 44.3 42.0 3600 45 43.8 45.9 3100 46 44.5 46.8 3100 47 39.3 15.3 6000 48 42.0 0.3 9700 49 43.1 12.1 8500 50 42.2 -5.3 8300 51 43.1 9.3 7900 52 45.1 13.4 5100 53 44.1 1.3 7900 54 42.9 16.2 5100 55 41.5 10.3 5500 *56 35.7 60.5 870 *57 29.5 21.3 620 58 40.2 45.9 4000 59 65.5 48.9 3300 60 55.8 48.1 4100 *61 82.9 151.8 830 *62 86.8 213.3 420 63 42.8 14.3 4800 64 45.6 20.0 4700 65 43.7 28.7 4000 66 45.7 19.5 4900 67 42.9 16.3 4600 68 40.2 7.3 4200 69 37.1 4.2 4000 70 45.8 19.7 4700 71 44.5 14.1 4900 72 47.0 35.4 4700 73 43.7 19.8 5100 74 44.2 40.2 4700 75 42.7 14.0 5100 76 43.8 10.5 6700 77 45.2 30.4 7100 78 42.9 9.3 7200 79 41.5 8.5 7500 80 35.2 0.1 6000 81 32.3 -9.8 5200 82 34.2 -5.3 4300 83 45.1 17.3 5700 84 43.8 6.7 7500 85 40.1 9.8 8500 86 41.8 4.9 7300 87 43.4 9.8 7200 88 42.9 8.7 6800 89 61.2 48.5 3500 90 41.2 -25.8 8500 91 40.3 -35.7 9200 92 40.7 -36.4 6300 93 44.3 -24.1 5800 94 42.5 -34.2 4900 95 42.8 -17.5 8100 96 44.5 -3.2 7000 97 52.1 38.5 3800 *98 59.3 58.3 910 As is apparent from the results shown in Table 5, in dielectric resorators comprising dielectric ceramic compositions within a composition range of the invention, the dielectric constant is kept at a high value at microwave frequencies, while a high unloaded Q value is provided. On the contrary, when use small celler x is higher than 0.60, the unloaded Q value is significantly reduced as observed in sample Nos. 56 and 57. The objects of the invention cannot readily be achieved. When x is lower than 0.10, the unloaded Q value is reduced as observed in Example Nos. 61 and 62. When y is higher than 0.60, the unloaded Q value is significantly reduced as observed in sample No. 38. Further, when y is lower than 0.20, the unloaded Q value is significantly reduced as observed in sample Nos. 27 to 30 and No. 39. Consequently, the objects of the invention cannot readily be achieved. When z is higher than 0.70, the unloaded Q value is reduced as observed in sample No. 39. Further, when z is lower than 0.01, the unloaded Q value is reduced as observed in sample No. 42. Consequently, the objects of the invention cannot readily be achieved. Additionally, the unloaded Q value can be improved by increasing u to a higher value than 0. However, when u exceeds 1.90, the unloaded Q value is reduced as observed in sample No. 82. Also in the case of sample No. 82, the properties were better than those of conventional dielectric ceramics. When the amount of accessory component to be added is higher than 7.000 % by weight, the unloaded Q value is significantly reduced as observed in sample No. 98. Consequently, the objects of the invention cannot readily be achieved. It was confirmed within the composition range of the example that the unloaded Q value was improved by using A, which is at least one element selected from Mg, Co, Zn, Ni, and Mn and B, which is at least one element selected from Nb and Ta, oxides were calcined in advance at a temperature of 800 to 1200°C. Additionally, a ZrTiO 4 phase or one recognized as being a crystallographical ZrTiO 4 phase was confirmed by powder X-ray diffraction of a dielectric ceramic within the composition range of Examples 1 and 2 of the invention. It was further confirmed in composition analysis by a local X-ray diffractometer of a fracture surface and polished surface of the dielectric ceramic having, as the main component, ZrTiO 4 phase or crystallographical ZrTiO 4 phase that all components of Zr, Ti, A and B (wherein A is at least one component selected from Mg, Co, Zn, Ni and Mn, and B is at least one component selected from Nb and Ta) were present in a single grain, and their composition ratio was consistent with the composition ratio between other grains that constitute the main phase in the same dielectric ceramic. It was also confirmed that all components A and B blended were present in a single grain. Moreover, it was confirmed that a dielectric resonator comprising a dielectric ceramic with components Zr, Ti, A and B present in a grain which constitutes the main phase showed a higher lattice constant in comparison with ZrTiO 4 ceramic obtained under the same sintering conditions. Accordingly, it was confirmed that components A and B are substituted in the ZrTiO 4 phase or the crystallographical ZrTiO 4 phase. Such dielectric ceramics specifically showed a high unloaded Q value and a high dielectric constant, and were superior in thermo-stability at a resonant frequency. The unloaded Q value was even higher when the molar ratio a/b of the component A to the component B was 0.5 or more and 1.9 or less. As is apparent from the results described above, it was confirmed that dielectric resonators comprising the dielectric ceramics of the example are capable of maintaining the dielectric constant at a high value at microwave frequencies, while providing a high unloaded Q value, and are superior in thermo-stability at a resonant frequency. Example 3 As initial materials, ZrO 2 , TiO 2 , MgO, CoO, ZnO, NiO, MnCO 3 , Nb 2 O 5 , Ta 2 O 5 , SnO 2 , HfO 2 , GeO 2 , BaCO 3 , SrCO 3 , CaCO 3 , CuO, Bi 2 O 3 , and WO 3 of high chemical purity which are the same as in Example 1 were used, weighed so as to make predetermined compositions and wet-blended with ethanol by using a ball mill. The volume ratio between the powder and ethanol was approximately 2:3. The mixture was removed from the ball mill, dried, and calcined for 2 to 8 hrs at 800°C to 1250°C in the air. The calcined product was wet-milled in the ball mill with ethanol. After the milled slurry was removed from the ball mill and dried, the powder was mixed with 8 % by weight of polyvinyl alcohol solution of 6 vol.% in concentration added thereto as a binder, homogenized, and granulated by sieving through a 32 mesh screen. The granulated powder was molded into a disk of 7 mm in diameter and approximately 3 mm in thickness by using molds and an oil hydraulic press at a molding pressure of 1.3 ton/cm 2 . The molding was placed in a magnesia vessel of high purity, kept in the air at a temperature of 400°C to 700°C for 4 to 8 hrs to remove binders, retained in the air at 1200°C to 1650°C for 1 to 100 hrs for sintering, and dielectric ceramics were obtained. The resonant frequency, unloaded Q (Qu) value and dielectric constant ε r were obtained from measurement by the dielectric rod resonator method. The temperature coefficient at a resonant frequency τ f was obtained in a range between -25°C and 85°C. The resonant frequency was obtained in a range between 4 GHz and 12GHz. The compositions of main components and the amount of accessory components, which are to be added, of the dielectric ceramics thus produced are shown in Table 6. The dielectric constant thus obtained, the temperature at a resonant frequency τ f (ppm/°C) and the unloaded Q value are shown in Table 7. In Tables 6 and 7, comparative examples have an asterisk. Sample No. A B D Composition of main component Accessory (molar fraction) (value) component x y z v u (wt.%) *99 Mg Nb Sn 0.400 0.150 0.400 0.050 0 Sr 0.005 100 Mg Nb Sn 0.200 0.200 0.400 0.200 0 Sr 1.000 101 Co Nb Sn 0.200 0.200 0.400 0.200 0 Sr 1.000 102 Ni Nb Sn 0.200 0.200 0.400 0.200 0 Sr 1.000 103 Mg Nb Sn 0.450 0.200 0.300 0.050 0 Sr 0.500 104 Co Nb Sn C.450 0.200 0.300 0.050 0 Sr 0.500 105 Mg Nb Sn 0.200 0.600 0.100 0.100 0 Ba 0.500 106 Zn Nb Sn 0.200 0.600 0.150 0.050 0 Ba 0.500 *107 Mg Nb Sn 0.150 0.700 0.100 0.050 0 Sr 1.000 *108 Mg Nb Sn 0.150 0.120 0.530 0.200 0 Ba 0.500 109 Mg Nb Sn 0.100 0.200 0.500 0.200 0 Ba 0.500 *110 Mg Nb Sn 0.100 0.200 0.300 0.400 0 Ba 0.500 *111 - - - 0.550 0.450 0 0 0 - 0 112 Mg Nb Sn 0.490 0.450 0.010 0.050 0 Ba 0.005 113 Mg Nb Sn 0.300 0.300 0.300 0.100 0 Sr 1.000 114 Mg Nb Sn 0.400 0.400 0.199 0.001 0 Sr 0.005 115 Co Nb Sn 0.400 0.400 0.199 0.001 0 Sr 0.005 116 Zn Nb Sn 0.400 0.400 0.199 0.001 0 Sr 0.005 117 Mg Nb Sn 0.450 0.450 0.050 0.050 0 Sr 0.100 *118 Mg Nb Sn 0.650 0.200 0.050 0.050 0 Ca 0.100 119 Mg Nb Sn 0.600 0.300 0.050 0.050 0 Ca 0.100 *120 Mg Nb Sn 0.050 0.500 0.400 0.050 0 Ca 0.100 121 Mg Nb Sn 0.450 0.350 0.150 0.050 0 Sr 1.000 122 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 Cu 0.005 123 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 Cu 0.100 124 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 W 0.005 125 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 W 0.100 126 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 W 1.000 127 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 W 2.000 128 Mg Nb Sn 0.350 0.450 0.150 0.050 0 Sr 1.000 129 Mg Nb Sn 0.350 0.450 0.150 0.050 0.01 Sr 1.000 130 Mg Nb Sn 0.350 0.450 0.150 0.050 0.05 Sr 1.000 131 Mg Nb Sn 0.350 0.450 0.150 0.050 0.20 Sr 1.000 132 Mg Nb Sn 0.350 0.450 0.150 0.050 0.50 Sr 1.000 133 Mg Nb Sn 0.350 0.450 0.150 0.050 1.00 Sr 1.000 134 Mg Nb Sn 0.350 0.450 0.150 0.050 1.90 Sr 1.000 135 Co Nb Sn 0.350 0.450 0.150 0.050 1.90 Sr 1.000 136 Mg Nb Sn 0.350 0.450 0.150 0.050 2.00 Sr 1.000 137 Mg 1/4 Nb Sn 0.340 0.520 0.130 0.010 0 Sr 0.100 Co 1/4 Zn 1/4 Ni 1/4 138 Mg 1/3 Ta Sn 0.340 0.520 0.130 0.010 1.00 Sr 0.100 Co 1/3 Ni 1/3 139 Mg 1/4 Nb 1/2 Sn 0.340 0.520 0.130 0.010 1.00 Sr 0.100 Co 1/4 Ta 1/2 Zn 1/4 Ni 1/4 140 Mn Nb Sn 0.200 0.600 0.190 0.010 0 Ca 0.100 141 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 0.500 142 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Ba 0.500 143 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Ca 0.500 144 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Bi 0.500 145 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Ba 0.500 Sr 0.500 Ca 0.500 Bi 0.500 146 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.500 147 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 3.000 148 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 7.000 *149 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 8.000 150 Mg Nb Hf 0.350 0.450 0.150 0.050 1.90 Sr 1.000 151 Mg Nb Ge 0.350 0.450 0.150 0.050 1.90 Sr 1.000 Sample No. ε r τ f Qu *99 29.8 -85.3 1200 100 27.6 -20.4 9600 101 26.7 -17.5 7500 102 28.3 -15.4 6900 103 31.7 -34.0 4000 104 32.9 -22.5 4100 105 55.4 28.3 5500 106 53.1 15.3 5800 *107 74.3 225.0 480 *108 21.3 -91.2 1200 109 30.2 -14.5 8600 *110 24.3 -60.5 400 *111 45.8 250.8 1800 112 42.5 23.2 4800 113 37.2 7.8 6500 114 41.5 -0.2 8300 115 43.0 11.5 7800 116 42.0 -5.8 6800 117 40.1 4.2 5100 *118 33.0 60.0 320 119 40.1 42.3 3100 *120 82.3 147.2 200 121 42.1 10.3 4100 122 43.1 15.5 4000 123 41.0 25.7 3800 124 43.1 15.1 4200 125 40.9 11.9 4000 126 38.0 3.1 3700 127 35.4 -1.0 3500 128 43.2 15.3 4000 129 42.9 14.9 4500 130 41.2 3.2 5000 131 40.5 0.2 6100 132 37.2 -4.5 6300 133 34.3 -15.5 7000 134 30.1 -32.5 7100 135 30.9 -35.4 5800 136 28.9 -37.4 3900 137 44.7 15.3 5100 138 39.7 9.3 8100 139 40.9 4.5 6500 140 60.3 44.9 3800 141 37.9 -30.3 7800 142 36.1 -35.4 8100 143 36.9 -35.1 5400 144 42.3 -25.9 3800 145 40.1 -33.2 3500 146 39.3 -20.1 6900 147 44.5 1.2 5800 148 50.2 39.5 4100 *149 61.5 65.4 320 150 45.3 -28.5 5300 151 30.9 -34.5 4900 As is apparent from the results shown in Table 7, it was confirmed that, in dielectric resonators comprising dielectric ceramic compositions within a composition range of the present invention, the dielectric constant is kept at a high value at microwave frequencies, while a high unloaded Q value is provided. On the contrary, when use small celler x is higher than 0.60, the unloaded Q value is significantly reduced as observed in sample No. 118. Consequently, the objects of the invention cannot readily be achieved. When x is lower than 0.10, the unloaded Q value is reduced as observed in sample No. 120. Consequently, the objects of the invention cannot readily be achieved. When y is higher than 0.60, the unloaded Q value is significantly reduced as observed in sample No. 107. Further, when y is lower than 0.20, the unloaded Q value is significantly reduced as observed in sample Nos. 99 and 108. Consequently, the objects of the invention cannot readily be achieved. When z is higher than 0.50, the unloaded Q value is reduced as observed in sample No. 108. When z is lower than 0.01, the unloaded Q value is reduced as observed in sample No. 111. Consequently, the objects of the invention cannot readily be achieved. Additionally, the unloaded Q value can be improved by increasing w to a higher value than 0. However, when w exceeds 1.90, the unloaded Q value is reduced as shown in sample No. 136. Also in the case of sample No. 136, the properties were better than those of conventional dielectric ceramics. When the amount of accessory component to be added is higher than 7.000 % by weight, the unloaded Q value is significantly reduced as observed in sample No. 149. Consequently, the objects of the invention cannot readily be achieved. It was confirmed within the composition range of the example that the unloaded Q value was improved by using A, which is at least one element selected from Mg, Co, Zn, Ni, and Mn and B, which is at least one element selected from Nb and Ta, oxides that were calcined in advance at a temperature of 800°C to 1200°C. Additionally, a ZrTiO 4 phase or one recognized as being a crystallographical ZrTiO 4 phase was confirmed by powder X-ray diffraction of a dielectric ceramic within the composition range of Examples 1 and 3 of the invention. It was further confirmed in composition analysis by a local X-ray diffractometer of a fracture surface and polished surface of the dielectric ceramic having as the main component ZrTiO 4 phase or crystallographical ZrTiO 4 phase, that all components of Zr, Ti, A, B and D (wherein A is at least one component selected from Mg, Co, Zn, Ni and Mn, B is at least one component selected from Nb and Ta, and D is at least one component selected from Sn, Hf and Ge) were present in a single grain, and their composition ratio was consistent with the composition ratio between other grains that constitute the main phase in the same dielectric ceramic. It was also confirmed that all components A, B and D blended were present in a single grain. Moreover, it was confirmed that a dielectric ceramic with components Zr, Ti, A, B and D present in a grain which constitutes the main phase showed a higher lattice constant in comparison with ZrTiO 4 ceramic obtained under the same sintering conditions. Accordingly, it was confirmed that components A, B and D are substituted in the ZrTiO 4 phase or the crystallographical ZrTiO 4 phase. Such dielectric resonators specifically showed a high unloaded Q value and a high dielectric constant, and were superior in thermo-stability at a resonant frequency. The unloaded Q value was even higher when the molar ratio a/b of the component A to the component B was 0.5 or more and 1.9 or less As is obvious from the results described above, it was confirmed that the dielectric resonators comprising the dielectric ceramics of the example are capable of maintaining the dielectric constant at a high value at microwave frequencies, while providing a high unloaded Q value, and are superior in thermo-stability at a resonant frequency. Example 4 As initial materials, ZrO 2 , TiO 2 , MgO, CoO, ZnO, NiO, MnCO 3 , Nb 2 O 5 , Ta 2 O 5 , BaCO 3 , SrCO 3 , CaCO 3 , CuO, Bi 2 O 3 , and WO 3 of high chemical purity were used, weighed so as to make predetermined compositions and wet-blended with ethanol by using a ball mill. The volume ratio between the powder and ethanol was approximately 2:3. The mixture was removed from the ball mill, dried, and calcined for 2 to 8 hrs at 800°C to 1250°C in the air. The calcined product was wet-milled in the ball mill with ethanol. After the milled slurry was removed from the ball mill and dried, the powder was mixed with 8 % by weight of polyvinyl alcohol solution of 6 vol.% in concentration added thereto as a binder, homogenized, and granulated by sieving through 32 mesh screen. The granulated powder was molded into a cylindrical coaxial shape by using molds and an oil hydraulic press at a molding pressure of 1.3 ton/cm 2 . The molding was placed in a magnesia vessel of high purity, kept in the air at a temperature of 400°C to 700°C for 4 to 8 hrs to remove binders, retained in the air at 1200°C to 1650°C for 1 to 100 hrs for sintering, and cylindrical coaxial dielectric ceramics having an outer diameter of 7.2 mm and an inner diameter of 3.6 mm were obtained. When copper was used for an electrode material, a copper coat having a thickness of about 3.5 µm was formed on the dielectric ceramic surface by the electroless plating method. When silver was used for the electrode material, silver paste which is on the market was burned to form a silver coat. In both cases, one of two end faces of the coaxial type device ground the electrode material, so that a TEM mode resonator was obtained. The compositions of main components and the amount of accessory components, which are to be added, of the dielectric resonator thus produced are shown in Table 8, the electrode material which was used, the unloaded Q value and the bond strength are shown in Table 9. The resonant frequency was 1.3 to 1.7 GHz. In Tables 8 and 9, comparative examples have an asterisk. Sample No. A B Composition of main component Accessory (molar fraction) (value) component(wt.%) x y z u *152 Mg Nb 0.340 0.520 0.140 0 - 0 *153 - - 0.550 0.450 0 0 - 0 154 Mg Nb 0.340 0.520 0.140 0 Sr 0.100 155 Co Nb 0.340 0.520 0.140 0 Sr 0.100 156 Zn Nb 0.340 0.520 0.140 0 Sr 0.100 157 Ni Nb 0.340 0.520 0.140 0 Sr 0.100 158 Mg Nb 0.100 0.400 0.500 0 Bi 0.100 159 Ni Nb 0.100 0.400 0.500 0 Bi 0.100 160 Mg Nb 0.450 0.350 0.200 0 Sr 1.000 161 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 Cu 0.005 162 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 Cu 0.100 163 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 0.005 164 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 0.100 165 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 1.000 166 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 W 2.000 167 Mg Nb 0.350 0.450 0.200 0 Sr 1.000 168 Mg Nb 0.350 0.450 0.200 0.05 Sr 1.000 169 Mg Nb 0.350 0.450 0.200 0.20 Sr 1.000 170 Co Nb 0.350 0.450 0.200 0.20 Sr 1.000 171 Mg Nb 0.350 0.450 0.200 0.50 Sr 1.000 172 Mg Nb 0.350 0.450 0.200 1.00 Sr 1.000 173 Mg Nb 0.350 0.450 0.200 1.90 Sr 1.000 174 Co Nb 0.350 0.450 0.200 1.90 Sr 1.000 175 Mg 1/3 Co 1/3 Ta 0.340 0.520 0.140 1.00 Sr 0.100 Ni 1/3 176 Mg 1/4 Co 1/4 Nb 1/2 0.340 0.520 0.140 1.00 Sr 0.100 Zn 1/4 Ni 1/4 Ta 1/2 177 Mg 39/40 Nb 1/2 0.340 0.520 0.140 0.02 Bi 0.100 Mn 1/40 Ta 1/2 178 Mg 113/200 Nb 0.328 0.502 0.170 0.41 Bi 0.100 Mn 87/200 179 Mg Nb 0.300 0.400 0.300 1.00 Ba 0.500 180 Mg Nb 0.300 0.400 0.300 1.00 Ca 0.500 181 Mg Nb 0.300 0.400 0.300 1.00 Bi 0.500 182 Mg Nb 0.300 0.400 0.300 1.00 Ba 0.500 Sr 0.500 Ca 0.500 Bi 0.500 183 Mg Nb 0.300 0.400 0.300 1.00 Sr 1.500 184 Mg Nb 0.300 0.400 0.300 1.00 Sr 1.500 185 Mg Nb 0.300 0.400 0.300 1.00 Sr 3.000 186 Mg Nb 0.300 0.400 0.300 1.00 Sr 7.000 *187 Mg Nb 0.300 0.400 0.300 1.00 Sr 8.000 Sample No. Electrode Qu Bond strength material (kg/4mm 2 ) *152 Cu 150 0.4 *153 Cu Unmeasurable due to electrode peeling 154 Cu 550 6.8 155 Cu 520 6.4 156 Cu 500 6.3 157 Cu 510 6.0 158 Cu 530 6.1 159 Cu 500 6.3 160 Cu 630 9.7 161 Cu 670 12.0 162 Cu 650 12.0 163 Cu 660 11.5 164 Cu 650 10.9 165 Cu 620 10.7 166 Cu 600 11.0 167 Cu 650 9.3 168 Cu 670 9.1 169 Cu 690 9.5 170 Cu 670 9.1 171 Cu 710 8.8 172 Cu 740 9.6 173 Cu 750 9.0 174 Cu 740 8.9 175 Cu 580 7.3 176 Cu 620 9.1 177 Cu 640 7.8 178 Cu 630 7.5 179 Cu 640 9.7 180 Cu 530 6.1 181 Cu 610 9.3 182 Cu 670 11.5 183 Cu 750 10.4 184 Ag 730 12.0 185 Cu 740 11.5 186 Cu 680 12.0 *187 Cu 210 10.5 As is apparent from the results shown in Table 9, the dielectric resonators of the embodiment had a high bond strength also when an electroless copper electrode is used in the same way as a silver electrode. For this reason, the unloaded Q value is high in a microwave frequency band and the resonant frequency can be prevented from deviating due to electrode peeling so that electric characteristics are stable. In addition, the dielectric resonators of the invention are suitable for forming electrodes by copper plating, so that they are suitable for large scale production and manufacturing costs can be reduced. Additionally, a ZrTiO 4 phase or one recognized as being a crystallographical ZrTiO 4 phase was confirmed by powder X-ray diffraction of a dielectric ceramic within the composition range of Example 4 of the invention. It was further confirmed in composition analysis by a local X-ray diffractometer of a fracture surface and polished surface of the dielectric ceramic having as the main component ZrTiO 4 phase or crystallographical ZrTiO 4 phase, that all components of Zr, Ti, A and B (wherein A is at least one component selected from Mg, Co, Zn, Ni and Mn, and B is at least one component selected from Nb and Ta) were present in a single grain, and their composition ratio was consistent with the composition ratio between other grains that constitute the main phase in the same dielectric ceramic. It was also confirmed that all components A and B blended were present in a single grain. Moreover, it was confirmed that a dielectric ceramic with components Zr, Ti, A and B present in a grain which constitutes the main phase showed a higher lattice constant in comparison with ZrTiO 4 ceramic obtained under the same sintering conditions. Accordingly, it was confirmed that components A and B are substituted in the ZrTiO 4 phase or the crystallographical ZrTiO 4 phase. Such dielectric ceramics specifically showed a high unloaded Q value and a high dielectric constant, and were superior in thermo-stability at a resonant frequency. The unloaded Q value was even higher when the molar ratio a/b of the component A to the component B was 0.5 or more and 1.9 or less. The dielectric resonators having such dielectric ceramics had an unloaded Q value which is specially high, and a high electrode bond strength. As is obvious from the results described above, it was confirmed that the dielectric resonators of the example have the unloaded Q value which is specially high at a microwave frequency band. Moreover, the resonant frequency can be prevented from deviating due to electrode peeling. In addition, the dielectric resonators of the invention are suitable for forming electrodes by copper plating, so that they can be produced on a large scale and manufacturing costs can be reduced. Example 5 As initial materials, ZrO 2 , TiO 2 , MgO, CoO, ZnO, NiO, MnCO 3 , Nb 2 O 5 , Ta 2 O 5 , SnO 2 , HfO 2 , GeO 2 , BaCO 3 , SrCO 3 , CaCO 3 , CuO, Bi 2 O 3 , and WO 3 of high chemical purity which are the same as in Example 1 were used, weighed so as to make predetermined compositions and wet-blended with ethanol by using a ball mill. The volume ratio between the powder and ethanol was approximately 2:3. The mixture was removed from the ball mill, dried, and calcined for 2 to 8 hrs at 800°C to 1250°C in the air. The calcined product was wet-milled in the ball mill with ethanol. After the milled slurry was removed from the ball mill and dried, the powder was mixed with 8 % by weight of polyvinyl alcohol solution of 6 vol.% in concentration added thereto as a binder, homogenized, and granulated by sieving through 32 mesh screen. The granulated powder was molded into a cylindrical coaxial shape by using molds and an oil hydraulic press at a molding pressure of 1.3 ton/cm 2 . The molding was placed in a magnesia vessel of high purity, kept in the air at a temperature of 400°C to 700°C for 4 to 8 hrs to remove binders, retained in the air at 1200°C to 1650°C for 1 to 100 hrs for sintering, and cylindrical coaxial dielectric ceramics having an outer diameter of 7.2 mm and an inner diameter of 3.6 mm were obtained. When copper was used for an electrode material, a copper coat having a thickness of about 3.5 µm was formed on the dielectric ceramic surface by the electroless plating method. When silver was used for the electrode material, silver paste which is on the market was burned to form a silver coat. In both cases, one of two end faces of the coaxial type device ground the electrode material, so that a TEM mode resonator was obtained. The compositions of main components and the amount of accessory components, which are to be added, of the dielectric resonator thus produced are shown in Table 10, the electrode material which was used, the unloaded Q value and the bond strength are shown in Table 11. The resonant frequency is 1.3 to 1.7 GHz. Sample No. A B D Composition of main component Accessory component (wt.%) (molar fraction) (value) x y z v u 188 Mg 1/4 Nb Sn 0.340 0.520 0.130 0.010 0 Sr 0.100 Co 1/4 Zn 1/4 Ni 1/4 189 Mg 1/3 Ta Sn 0.340 0.520 0.130 0.010 1.00 Sr 0.100 Co 1/3 Ni 1/3 190 Mg 1/4 Nb 1/2 Sn 0.340 0.520 0.130 0.010 1.00 Sr 0.100 Co 1/4 Ta 1/2 Zn 1/4 Ni 1/4 191 Mn Nb Sn 0.200 0.600 0.190 0.010 0 Ca 0.100 192 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 0.500 193 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Ba 0.500 194 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Ca 0.500 195 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Bi 0.500 196 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Ba 0.500 Sr 0.500 Ca 0.500 Bi 0.500 197 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.000 Cu 0.005 198 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.000 Cu 0.100 199 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.000 W 0.005 200 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.000 W 0.100 201 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.000 W 1.000 202 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.000 W 2.000 203 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.500 204 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 1.500 205 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 3.000 206 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 7.000 *207 Mg Nb Sn 0.300 0.400 0.200 0.100 1.00 Sr 8.000 208 Mg Nb Hf 0.350 0.450 0.150 0.050 1.90 Sr 1.000 209 Mg Nb Ge 0.350 0.450 0.150 0.050 1.90 Sr 1.000 Sample No. Electrode material Qu Bond strength (kg/4mm 2 ) 188 Cu 580 8.8 189 Cu 540 6.1 190 Cu 590 8.3 191 Cu 480 5.1 192 Cu 670 9.3 193 Cu 600 9.1 194 Cu 480 5.7 195 Cu 540 8.7 196 Cu 720 10.8 197 Cu 760 12.0 198 Cu 740 12.0 199 Cu 730 10.9 200 Cu 740 11.4 201 Cu 700 9.7 202 Cu 650 8.9 203 Cu 760 10.8 204 Ag 720 12.0 205 Cu 720 11.1 206 Cu 700 11.3 *207 Cu 180 12.0 208 Cu 630 10.1 209 Cu 540 8.9 As is apparent from the results shown in Table 11, the dielectric resonators of the embodiment had a high bond strength also when an electroless copper electrode is used in the same way as a silver electrode. For this reason, the unloaded Q value is high in a microwave frequency band and the resonant frequency can be prevented from deviating due to electrode peeling so that electric characteristics are stable. In addition, the dielectric resonators of the invention are suitable for forming electrodes by copper plating, so that they are suitable for large scale production and manufacturing costs can be reduced. Additionally, a ZrTiO 4 phase or one recognized as being a crystallographical ZrTiO 4 phase was confirmed by powder X-ray diffraction of a dielectric ceramic within the composition range of Example 5. It was further confirmed in composition analysis by a local X-ray diffractometer of a fracture surface and polished surface of the dielectric ceramic having as the main component ZrTiO 4 phase or crystallographical ZrTiO 4 phase that all components of Zr, Ti, A, B and D (wherein A is at least one component selected from Mg, Co, Zn, Ni and Mn, B is at least one component selected from Nb and Ta, and D is at least one component selected from Sn, Hf and Ge) were present in a single grain, and their composition ratio was consistent with the composition ratio between other grains that constitute the main phase in the same dielectric ceramic. It was also confirmed that all components A, B and D blended were present in a single grain. Moreover, it was confirmed that a dielectric ceramic with components Zr, Ti, A, B and D present in a grain which constitutes the main phase showed a higher lattice constant in comparison with ZrTiO 4 ceramics obtained under the same sintering conditions. Accordingly, it was confirmed that components A, B and D are substituted in the ZrTiO 4 phase or the crystallographical ZrTiO 4 phase. Such dielectric ceramics specifically showed a high unloaded Q value and a high dielectric constant, and were superior in thermo-stability at a resonant frequency. The unloaded Q value was even higher when the molar ratio a/b of the component A to the component B was 0.5 or more and 1.9 or less. The dielectric resonators having such dielectric ceramics had an unloaded Q value which is specially high, and a high electrode bond strength. As is apparent from the results described above, it was confirmed that the dielectric resonators of the example have the unloaded Q value which is especially high at a microwave frequency band. Moreover, the resonant frequency can be prevented from deviating due to electrode peeling. In addition, the dielectric resonators of the invention are suitable for forming electrodes by copper plating, so that they can be produced on a large scale and manufacturing costs can be reduced. Although a dielectric ceramic having a cylindrical coaxial shape was used in Examples 4 and 5 of the invention, it is not limited to such a shape. For example, in the case of a TEM mode resonator using a dielectric ceramic having a prismatic coaxial or stepped coaxial shape, a microstrip line resonator using a dielectric resonator which has a planar shape, or a triplate resonator, an unloaded Q value which is equivalent to or more than the conventional ones can be obtained. Thus, a dielectric resonator in which stability is high and manufacturing costs are reduced can be obtained. According to the structure of the dielectric ceramic of the dielectric resonator the invention, the variation in temperature coefficient at a resonant frequency due to heat history during sintering of ZrTiO 4 and ZrO 2 -SnO2-TiO 2 ceramics can be reduced. In addition, a high unloaded Q value is provided, and the temperature coefficient at a resonant frequency can be changed as desired without reducing the dielectric constant. Furthermore, according to the structure of the dielectric resonator of the invention, a dielectric resonator having a high unloaded Q value and a strong electrode layer can be obtained.

Claims: A dielectric resonator comprising the dielectric ceramic comprising as a main component a complex oxide formed of both Zr and Ti, at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta, and as the accessory components at least one component selected from the group (C) consisting of Ba, Sr, Ca, Cu, Bi and W, wherein the main component of the dielectric ceramic is expressed by the Formula: xZrO 2 - yTiO 2 - zA (1+u)/3 B (2-u)/3 O 2 , wherein A denotes at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, B denotes at least one component selected from the group (B) consisting of Nb and Ta, wherein x, y, and z denote molar fractions and u denotes a value defined as follows: x + y + z = 1 0.10 ≦ x ≦ 0.60 0.20 ≦ y ≦ 0.60 0.01 ≦ z ≦ 0.70 0 ≦ u ≦ 1.90 and wherein the accessory components of the dielectric ceramic are present within the range of 0.005 to 7.000 % by weight based on the entire weight of the ceramic, characterized in that the dielectric resonator is a cylindrical coaxial dielectric resonator, in which copper (Cu) is coated on to the surface of the cylindrical dielectric ceramic (2) so to form copper electrodes and so that the electrodes are not formed on the surface of an opening end (3), wherein electromagnetic waves are incident in the direction of the opening end (3), and the resonance (TEM mode) of the electromagnetic waves in a specific frequency area is utilized to obtain the necessary output from the electrodes (1,4). The dielectric resonator according to claim 1, wherein the main component comprises a ZrTiO 4 or crystallographicai ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta. The dielectric resonator according to claim 1, wherein the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn and at least one component selected from the group (B) consisting of Nb and Ta, and a/b (a and b denote the total of molar fractions of the components A and B) ranges from 0.5 to 1.9. The dielectric resonator according to claim 1, wherein the complex oxide of the main component further comprises at least one component selected from the group (D) consisting of Sn, Hf and Ge. The dielectric resonator according to Claim 4, wherein the main component of the dielectric ceramic is expressed by the Formula: xZrO 2 - yTiO 2 - zA (1+u)/3 B (2-u)/3 O 2 - vDO 2 , wherein A denotes at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, B denotes at least one component selected from the group (B) consisting of Nb and Ta, and D denotes at least one component selected from the group (D) consisting of Sn, Hf and Ge, wherein x, y, z and v denote molar fractions and u denotes a value defined as follows: x + y + z + v = 1 0.10 ≦ x ≦ 0.60 0.20 ≦ y ≦ 0.60 0.01 ≦ z ≦ 0.50 0.001 ≦ v ≦ 0.20 0 ≦ u ≦ 1.90 The dielectric resonator according to claim 4, wherein the dielectric ceramic further comprises at least one accessory component selected from the group (C) consisting of Ba, Sr, Ca, Cu, Bi and W within the range from 0.005 to 7.000 % by weight based on the entire weight of the ceramic. The dielectric resonator according to claim 5, wherein the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, at least one component selected from the group (B) consisting of Nb and Ta, and at least one component selected from the group (D) consisting of Sn, Hf and Ge. The dielectric resonator according to claim 5, wherein the main component comprises a ZrTiO 4 or crystallographical ZrTiO 4 phase substituted with at least one component selected from the group (A) consisting of Mg, Co, Zn, Ni and Mn, at least one component selected from the group (B) consisting of Nb and Ta, and at least one component selected from the group (D) consisting of Sn, Hf and Ge, and a/b (a and b denote the total of molar fractions of the components A and B) ranges from 0.5 to 1.9.

Inventors: KAWASHIMA SYUNICHIRO, KUGIMIYA KOICHI, OKUYAMA KOJIRO, SHIMOYAMA KOJI, KAWASHIMA, SYUNICHIRO, KUGIMIYA, KOICHI, OKUYAMA, KOJIRO, SHIMOYAMA, KOJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1995
Main classification: C04B35
IPC codes: H01P7, H01G4, H01B3, C04B35