Background of the Invention In recent years, communication systems have developed which use microwaves (frequency band ranging from 300 MHz to 300 GHz). These systems include wireless telephones, car phones, cellular phones, satellite broadcasting systems, and the like. As a result, there is an increasing demand for dielectric ceramics with better electrical properties for use components such as resonator devices, band pass filters, and microwave integrated circuits.

Bismuth based pyrochlores have recently become of interest for use as high frequency dielectric materials. One of the bases for this interest is that they can be fired at low temperatures. In contrast to conventional microwave dielectric materials which require sintering temperatures of more than 1600 °K, Bismuth pyrochlores can be sintered at less than about 1400 °K. In addition, their dielectric properties such as a low loss of tan 5 of 10-4 and a K of up to about 150 make Bismuth pyrochlores promising dielectric material candidates.

For use in microwave communications systems which operate at high frequencies, dielectric materials should have properties such as high dielectric constant ("K"); high quality factor ("Q"); and stable temperature coefficient of capacitance ("TCC"). However, it is very difficult to develop dielectric materials which have a stable TCC as well as high K and high Q. A need therefore continues to exist for a dielectric material which has a high K, a high Q value and a stable TCC.

Brief Description of the Drawings Fig. 1 shows a ternary phase diagram of Bi203-ZnO-Ta205 and a compositional space defined by vertices A, B and C.

Summary of the Invention The present invention provides Bi203-ZnO-Ta205 dielectric materials which have both high K and high Q, and which can be fired at low temperatures such as less than about 1000 °C.

Compounds within the compositional space defined by vertices A, B and C of the Bi203-ZnO-Ta205 system shown in Fig.

1 are produced. These compounds are illustrated by Bi2 (ZnTa xO6x+3 where 0.57 < x < 1.0, by Bi (ZnTa) O where 1.0 < y < 3.0, as well as by Bi2 (ZnTay) 2/3O((ty+11)/3) 1.0 < y < 3.0 with the proviso that y is not = 2.0. In Fig. 1, vertex A is defined by 0.125 mol% Ta2O5, O. 125 mol% ZnO, 0.75 mol% Bi203i vertex B is defined by 0.125 mol% Ta2O5, 0.75 mol% ZnO, 0.125 mol% Bi 203 ; and vertex C is defined by 0.6875 mol% Ta2O5, 0.125 mol%ZnO, 0.1875 mol% Bi2O3.

Mixed phases and solid solutions on the tie line between the compounds of examples 5 and 8 within the compositional space A-B-C of FIG. 1, as defined by the formula r (Bi (Zn1/3Ta2/3)2O7)-((1-r) (Bi3/2Zn1/2) (Zn1/2Ta3/2)O7)) where 0 < r < 1, also are produced.

These compounds typically have a high K, high Q, a low TCC, and low TCF over the frequency range of 1 MHz-28 GHZ, and can be sintered between about 850 °C to about 1000 °C, preferably between about 850 °C to about 950 °C. Borosilicate glass in an amount of up to about 5 wt. % based on the weight of compound, preferably Bi2 (ZnTa2)2/3O7, may be added to the compound.

The Bi203-ZnO-Taz05 dielectric compounds of the invention have outstanding K, Q, TCC and temperature coefficient of resonant frequency ("TCF"). Typical properties include a K of 50-80, such as K > 60 at 5 GHz, low dielectric loss (tan 5 <0.003) such as a tan 5 < 0.001 at 5 GHz, a Q > 300 at 5 GHz, a Qf > 2000 at 5 GHZ, a TCF < 40 ppm/°C over the temperature range of-50°C to + 125 °C, a TCC < 50 ppm/°C such as a TCC of <30 ppm/°C over the temperature range of-50 °C to +125 °C.

Detailed Description of the Invention In a first embodiment, compounds of Bi2 (ZnTa2) xO6x+3 where 0.57 < x < 1. 0, of Bi2(ZnTay)2/3O((5y+11/3) where 1.0 < y zu 3.0 and of Bi2(ZnTay)2/3O((5y+11)/3) where 1.0 # y # 3.0 with the proviso that y is not = 2.0 are produced. Manufacture of these compounds is illustrated in examples 1-14.

Examples 1-14 In manufacture of compounds of the formula Bi2 (ZnTa2) xO6x+3, ZnO and Ta205 are reacted at 1000 °C to produce (ZnTa 2). 06. according to equation (1) : x (ZnO) + x (Ta2O5)# (ZnTa2)xO6x (1) The (ZnTa2) X°6x then is reacted at 1000 °C with Bi203 according to equation (1A) to produce a compound corresponding to Bi2 (ZnTa2) )xO6x+3: Bi2O3 + (ZnTa2)xO6x # Bi2(ZnTa2)xO6x+3 (1A) In manufacture of (ZnTa2) Xi6., reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and reagent grade Ta205 of 99.9% purity from Aldrich Chemical Co. are milled in deionized water in a ball mill. Milling is performed for 24 hours using yttrium-stabilized zirconia balls to produce a blend that has a particle size range of 0.3 to 1.5 microns, and an average particle size of 1.0 micron. The resulting milled particle blend is dried in air at 120 °C for 16 hours. The resulting dried particles are calcined at 1000 °C in an open alumina crucible for 4 hours to produce (ZnTa206) x Bi203 is mixed with the (ZnTa206) x powder. The resulting mixture is ball milled for 24 hours using yttrium-stabilized zirconia balls to produce a particle size range of 0.5 to 1.3 microns, and an average particle size of 0.8 microns. The milled particles are dried in air at 120 °C for 16 hours and calcined in an open alumina crucible at 800 °C for 4 hours.

The milled particles are blended with 1 wt. %, based on the weight of the calcined particles, of polyvinyl alcohol. The resulting mixture is uniaxially cold pressed at 6000 PSI and sintered in an open alumina crucible at 950-1100 °C to produce a sintered disk that measures 10 mm diameter and 1 mm thick.

In manufacture of compounds of the formula Bi (ZnTay)2/3O((5y +11)/3) t ZnO and Ta205 are reacted at 1000 °C to produce (ZnTay)2O5y+2 according to equation (2): 2ZnO + yTa2O5 # (ZnTay)2O5y+2 The (ZnTay)2O5y+2 then is reacted with 3Bi203 according to equation (2A) at 950-1100 °C to produce a compound corresponding to Bi2(ZnTay)2/3O((5y+11)/3) : 1/3 (ZnTay) 2°5y+2 + Bi2O3 # Bi2(ZnTay)2/3O((5y+11/3) (2A) In manufacture of (ZnTay)2O5y+2, reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and reagent grade Ta205 of 99.9% purity from Aldrich Chemical Co. are milled in deionized water in a ball mill. Milling is performed for 24 hours using yttrium-stabilized zirconia balls to produce a blend that has a particle size range of 0.3 to 1.5 microns, and an average particle size of 1.0 micron. The resulting milled particle blend is dried in air at 120 °C for 16 hours. The resulting dried particles are calcined at 1000 °C in an open alumina crucible for 4 hours to produce (ZnTay)2O5y+2.

Bi203 is mixed with the (ZnTay)2O5y+2 powder. The resulting mixture is ball milled for 24 hours using yttrium-stabilized zirconia balls to produce a particle size range of 0.5 to 1.3 microns, and an average particle size of 0.8 microns. The milled particles are dried in air at 120 °C for 16 hours and calcined in an open alumina crucible at 800°C for 4 hours. The milled particles are blended with 1 wt. %, based on the weight of the calcined particles, of polyvinyl alcohol. The resulting mixture is uniaxially cold pressed at 6000 PSI and sintered in an open alumina crucible at 950-1100 °C to produce a sintered disk that measures 10 mm diameter and 1 mm thick.

The amounts of reactants, sintering temperatures, and the compositions of the resulting compounds produced in examples 1-14 are shown in Table 1. Compounds 1-10 also are shown in FIG. 1.

Table 1<BR> Reactant oxides Final Compounds Ex. x y Ta2O5 ZnO Bi2O3 Sintering Ta2O5 Ta2O5 ZnO ZnO Bi2O3 Bi2O3 Mols. Mols. Mols. Temp.°C Mols. wt.% Mols. wt.% Mols. wt.% 1 0.57 - 0.57 0.57 1.0 1000 26.636 32.959 26.636 6.070 46.729 60.971 2 0.667 - 0.667 0.667 1.0 1000 28.578 36.165 28.578 6.661 42.845 57.174 3 0.8 - 0.8 0.8 1.0 1000 30.769 39.964 30.769 7.361 38.462 52.675 4 1.0 - 1.0 1.0 1.0 1000 33.333 44.670 33.333 8.227 33.333 47.103 5 0 - 0.758 1.0 0.75 1000 30.00 43.478 40.00 10.677 30.00 45.845 6 -- 1 0.2 0.4 0.6 1000 16.67 22.067 33.33 8.129 50.00 69.805 7 -- 1.5 0.3 0.4 0.6 1000 23.10 29.811 30.80 7.321 46.20 62.868 8 -- 2 0.4 0.4 0.6 1000 28.50 36.155 28.60 6.659 42.90 57.186 9 -- 2.5 0.5 0.4 0.6 1000y 33.33 41.447 26.70 6.107 40.00 52.446 10 -- 3.0 0.6 0.4 0.6 1000 37.50 45.929 25.00 5.640 37.50 48.431 11 0.645 -- 0.645 0.645 1.0 1000 28.166 35.473 28.166 6.534 43.669 57.993 12 0.656 -- 0.656 0.656 1.0 1000 28.374 35.822 28.374 6.598 43.253 57.580 13 0.676 -- 0.676 0.676 1.0 1000 28.778 36.504 28.778 6.723 42.445 56.773 14 0.69 -- 0.69 0.69 1.0 1000 28.992 36.868 28.992 6.790 42.017 56.342 Examples 15-23 In a second embodiment, composites and solid solutions of the formula r (Bi2(Zn1/3Ta2/3)2O7) - ((1-r) (Bi3/2Zn1/2) (Zn1/2Ta3/2)O7), 0 < r < 1, are produced as the reaction products of mixtures of Bi2(Zn1/3Ta2/3)2O7 and (Bi3/2Zn1/2)(Zn1/2Ta3/2)O7.

To illustrate, a series of mixtures of Bi2 (Znl/3Ta2/3) 2°7 (r=l) and (Bi3/2Zn1/2)(Zn1/2Ta3/2)O7 (r=0) powders are prepared according to the formula r (Bi2 (Zn1/3Ta2/3)2O7)-((1-r)(Bi3/2Zn1/2)(Zn1/2Ta3/2)O7), 0< r <1. These mixtures are prepared for (r) values of 0,0.2,0.3,0.4,0.5, 0.6,0.85, and 1.0, which correspond to examples 15-23, respectively. The powders are ball milled with yttrium stabilized zirconia balls to an average particle size of 1 micron. The milled powders are dried at 120 °C for 16 hours, mixed with 1 wt. % organic binder, and uniaxially compressed at 6000 PSI into 10 mm thick disks of 1 mm thickness. The disks are sintered at 1000 °C for 4 hours in air to produce the solid solution.

The Bi (Zm1/3Ta2/3)2O7 and the (Bi3/2ZnlZ2) (Zn1/2Ta3/2)O7 employed in examples 15-23 are produced as described below.

Manufacture of Bi2 (Zn/3Ta2/3) 2°7 15.55 gms. of reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and 84.45 gms. of reagent grade Ta205 of 99.9% purity from Aldrich Chemical Co. are milled in deionized water in a ball mill for 24 hours using yttrium-stabilized zirconia balls to produce a blend that has a particle size range of 0.3 to 1.5 microns, and an average particle size of 1.0 micron. The milled particle blend is dried in air at 120 °C for 16 hours. The resulting dried particles are calcined at 1000 °C in an open alumina crucible for 4 hours to produce ZnTa206.

57.19 gms. Bi are mixed with 42.81 gms. of the ZnTa206 powder. The resulting mixture is ball milled for 24 hours using yttrium-stabilized zirconia balls to produce a particle size range of 0.5 to 1.3 microns, and an average particle size of 0.8 microns. The milled particles are dried in air at 120 °C for 16 hours and calcined in an open alumina crucible at 800°C for 4 hours. The milled particles are blended with 1 wt. %, based on the weight of the calcined particles, of polyvinyl alcohol. The resulting mixture is uniaxially cold pressed at 6000 PSI and sintered in an open alumina crucible at 950 °C to produce a sintered disk of Bi2 (Znl/3Ta2/3) 207 that measures 10 mm diameter and 1 mm thick.

Manufacture of (Bi3/2Zn1/2)(Zn1/2Ta3/2)O7 15.55 gms. of reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and 84.45 gms. of reagent grade Ta of 99.9% purity from Aldrich Chemical Co. are milled in deionized water in a ball mill. Milling is performed for 24 hours using yttrium-stabilized zirconia balls to produce a blend that has a particle size range of 0.3 to 1.5 microns, and an average particle size of 1.0 micron. The milled particle blend is dried in air at 120 °C for 16 hours. The resulting dried particles are calcined at 1000 °C in an open alumina crucible for 4 hours to produce ZnTa206 45.85 gms. Bi203 and 2.67 gms. ZnO are mixed with the 51.48 gms. ZnTa206. The resulting mixture is ball milled for 24 hours using yttrium-stabilized zirconia balls to produce a particle size range of 0.5 to 1.3 microns, and an average particle size of 0.8 microns. The milled particles are dried in air at 120 °C for 16 hours and calcined in an open alumina crucible at 800 °C for 4 hours. The milled particles are blended with 1 wt. %, based on the weight of the calcined particles, of polyvinyl alcohol. The resulting mixture is uniaxially cold pressed at 6000 PSI and sintered in an open alumina crucible at 950 °C to produce a sintered disk of (Bi3/2Zn1/2)(Zn1/2Ta3/2)O7 that measures 10 mm diameter and 1 mm thick.

In manufacture of the Bi2(Zn1/3Ta2/3)2O7 and (Bi3/2Znl/2) (Znl/2T a3/2) °7 compounds as described above, reagent grade oxides of Bi2O3, ZnO and Ta205of a purity >99.9% is used. It should be noted however, that non-reagent grade oxides of about 99 % purity also can be used. In addition, binders other than polyvinyl alcohol can be used. Examples of other organic binders which may be used include but are not limited to polyethylene glycol, methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxpropylcellulose, polyethylene oxide base high polymers, acrylic base high polymers, maleic anhydride base high polymers, starch, gelatine, polyoxyethylene alkyl ether, polyvinyl butyrol and waxes. In addition, it should be noted that ball milling may be done in media other than deionized water. Examples of suitable media include acetone.

Examples 24-27 In another aspect, the Bi (Zn1/3Ta2/3)2O7 and (Bi3/2Zn1/2) (Zn1/2 Ta 3/2) 07 compounds each may be mixed with glass such as a P205 type glass, a PbO type glass, and a Bi203type glass, preferably a borosilicate glass, more preferably a ZnO-B2O3- SiO2 type borosilicate glass, and then fired. The amount of glass added to these compounds may be up to about 5 wt. % based on the weight of the compound, preferably about 0.5 wt. %.

To illustrate, a borosilicate glass of the composition ZnO-B203-SiO2 is added to Bi2 (Zn1/3Ta2/3)2O7 to produce a blend.

The blend then is ball milled in water with yttrium stabilized zirconia balls for 24 hours to produce an average particle size of 0.5 microns. The resulting milled powder is then mixed with 1 wt. % of polyvinyl alcohol binder based on the weight of the milled power. The resulting blend is uniaxially compressed at 6000 PSI into a pellet.

The sintering temperatures of various blends of Bi2 (Zn1/3Ta2/3)2O7 and the ZnO-B2O3-SiO2 borosilicate glass of composition 60 wt. on-30 wt. %B2O3-10 wt. %SiO2 are shown in Table 2. The dielectric properties, as measured according to the procedures described below, of the blend of Bi2 (Zn1/3Ta2/3) 2°7 and 0.5 wt. % borosilicate glass sintered at 850 °C, when measured at room temperature a frequency of 100 KHZ, are K = 58.9, Q= 1400 and TCC = 50.0.

Table 2 Example 24 25 26 27 Borosilicate glass (wt. %) * 0. 0 0.5 1.0 2. 0 Sintering Temp. °C 1050ui 850 800 780 *. Based on weight of Bi2(Zn1/3Ta2/3)2O7 Reacted blends of Bi2 (Zn1/3Ta2/3) 207and glass, (Bi3/2Zn1/2)(Zn1 Ta3/2) O7 and glass, as well as mixtures thereof, also may be used to prepare solid solutions and composites as in the manner described above.

Dielectric property measurement Gold electrodes then are sputtered onto each side of the sintered disk and the dielectric properties evaluated. The dielectric properties of each of sintered Bi2 (Zn1/3a2/3)2O7, sintered Bi2 (Zn1/3Ta2/3) 207 with glass, sintered (Bi3/2znl/2) (Znl/2Ta3 /2) 07, as well as sintered solid solutions of Bi2 (Zn1/3Ta2/3)2O7 and (Bi3/2zn1/2)(Zn1/2Ta3/2)O7 are measured.

Measurement of dielectric properties such as (K, tan 5 and TCC) at low frequencies of 1KHz to lMHz is done while cooling at a rate of 2°C/min. over the temperature range of +150°C to-170°C in conjunction with a computer interfaced temperature chamber-chamber from Delta Design Corp., San Diego, CA. The temperature is monitored with a K-type thermocouple or a Pt sensor. Measurements are made by using a Hewlett-Packard 4284 Inductance-Capacitance-Resistance ("LCR") meter. An AC field of 0.1 V/mm is applied to 10 mm diameter sintered pellets.

The (TCC, ppm/°C) is calculated from the slope of the dielectric constant (K) over the temperature range of +120°C to-55°C and the dielectric constant at 25°C. Measurement of dielectric properties (K, tan 5 and TCC) at high frequencies of 400MHz to 20 GHZ is done over the temperature range of +150°C to-170°C by using the well known Hakki-Coleman method with a Hewlett-Packard HP 8510C network-spectrum-analyzer.

The measured properties are shown in Tables 3 to 7.

Table 3<BR> Room Temperature K, Q and TCC at 1k Hz for Bi2(ZnTa2)xO6x+3 Sintered at Various temperatures 950°C 1000°C 1050°C 1100°C Ex. x K Q TCC K Q TCC K Q TCC K Q TCC 1 0.571 64.9 1379 75.1 67.2 1212 90.3 71.7 115 223.9 78.8 56332.1 2 0.667 61.1 1053 39.L5 60.8 1600 43.2 60.2 519 72.3 602. 755 76.1 3 0.85 33.5 1667 -14.3 56.8 1250 -8.1 62.9 6667 -18.4 63.1 1250 20.9 4 1.000 45.8 1429 -61.1 63.6 1212 -69.6 65.6 1143 -76.5 67.5 1379 -72.7 11 0.645 62.8 4000 54.9 62.9 4000 57.7 64.9 476 87.7 63.1 131 165.4 12 0.656 61.9 4444 50.5 61.9 4000 55.5 64.0 404 75.9 62.0 185 126.4 13 0.678 47.7 1177 4.4 61.6 1026 24.0 63.0 1212 38.2 61.8 1143 41.3 14 0.690 29.9 1667 -0.9 42.3 1177 11.2 62.9 1250 26.1 59.0 1177 61.7 Table 4<BR> Dielectric Properties at Room Temperature, at 1 MHz Example r Sintering Temp.°C Sintering Time Hr. K tan # TCC 15 0 1000 4 71.4 <0.05 -172ppm/C 16 0.2 1000 4 77.5 <0.003 -164 17 0.3 1000 4 76.9 <0.003 -143 18 0.4 1000 4 72.9 <0.003 -106 19 0.5 1000 4 70.7 <0.002 -62 20 0.6 1000 4 68.3 <0.002 -21 21 0.7 1000 4 460.8 <0.002 9.5 22 0.85 1000 4 64.3 <0.002 59 23 1 950 4 60.8 <0.001 60 Table 5<BR> K at 1MHz over the range of -160°C to +120°C (Compounds Sintered at 1000°C for 4 hrs) Example r -160°C -120°C -80°C 0°C 40°C 80°C 120°C 15 0.0 72.8 74.3 74.1 73.3 72.9 72.4 71.9 16 0.2 77.3 78.9 78.6o 77.8 77.3 76.7 76.1 17 0.3 76.7 78.0 77.8 771 76.7 76.2 75.7 18 0.4 72.8 74.0 73.7 73.0 72.8 72.4 72.1 19 0.5 70.2 71.0 70.9 70.7 70.6 70.4 70.1 20 0.6 67.8 68.2 68.3 68.3 68.3 68.2 68.1 21 0.74 60.3 60.8 60.7 60.7 60.8 60.8 60.8 22 0.8 63.3 63.5 63.8 64.2 64.4 64.5 64.6 23 1.0 60.5 61.0 61.3 61.7 62.0 62.2 62.3 Table 6<BR> K ati 10KHz over the range of -160C to +120°C (Compounds Sintered at 1000°C for 4 hrs) Example r -160°C -120°C -80° 0°C 40°C 80°C 20°C 15 0.0 74.6 74.7 74.4 73.6 73.1 72.6 72.1 16 0.2 78.4 78.4 78.1 77.2 76.6 76.1 75.5 17 0.3 77.2 77. 276.9 76. 275.1 75.2 74.7 18 0.4 73.1 73.0 72.8 72.2 71.9 71.5 71.2 19 0.5 70.8 70.9 70.8 70.6 70.4 70.2 70.0 20 0.6 68.5 68.6 68.6 68.7i 68.6 68.5 68.4 21 0.74 57.9 58.1 58.0 58.0 58.1 58.1 58.1 22 0.8 62.7 62.9 63.1 63.3 63.8 63.9 64.0 23 1.0 60.8 61.1 61.3 61.9 62.2 62.5 62.7 Table7<BR> tan # at 1MHz over the range of -160C to +120°C (Sintered at 1000°C for 4 hrs) Example r -160°C -120°C -80°C 0°C 40°C 80°C 120°C 15 0 0.03 <0.004 <0.004 0.001 <0.004 <0.004 <0.004 16 0.2 0.01 0.003 <0.003 <0.003 <0.003 <0.003 <0.003 17 0.3 0.013 0.002 <0.003 <0.003 <0.003 <0.003 <0.003@ 18 0.4 0.03 0.003 <0.003 <0.003 <0.003 <0.003 <0.003 19 0.5 0.007 0.002 <0.002 <0.002 <0.002 <0.002 <0.002 20 0.6 0.0043 0.002 <0.002 <0.002 <0.002 <0.002 <0.002 21 0.74 0.002 0.002 <0.002 <0.002 <0.002 <0.002 <0.002 22 0.8 0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 23 1.0 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001