Bismuth pyrochlore microwave dielectric materials

Abstract

The disclosed invention relates to Bi2O3—ZnO—Ta2O5 dielectric compounds and compositions, and to their manufacture. The compounds of the invention have outstanding K, Q, TCF, and TCC. Examples of these properties include a K of between 58 and 80, a low dielectric loss (tan δ<0.003), and a TCC<30 ppm/° C. Ceramic compositions produced include those represented by Bi2(ZnTa2)xO6x+3 where 0.57≦x≦1.0, Bi2(ZnTay)⅔O((5y+11)/3) where 1.0≦y≦3.0, as well as by Bi2(ZnTay)⅔O((5y+11)/3) where 1.0≦y≦3.0 with the proviso that y is not=2.0. Solid solutions of compounds defined by the formula r(Bi2(Zn⅓Ta⅔)2O7)-(1−r)(Bi{fraction (3/2)}Zn⅔)(Zn½Ta{fraction (3/2)})O7))where 0

Description

FIELD OF THE INVENTION

[0002] The present invention relates to dielectric ceramic compositions for microwave applications and, more particularly, to Bi2O3—ZnO—Ta2O5 dielectric ceramic compositions for microwave devices.

BACKGROUND OF THE INVENTION

[0003] 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.

[0004] 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 δ of 10−4 and a K of up to about 150 make Bismuth pyrochlores promising dielectric material candidates.

[0005] 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

[0006] FIG. 1 shows a ternary phase diagram of Bi2O3—ZnO—Ta2O5 and a compositional space defined by vertices A, B and C.

SUMMARY OF THE INVENTION

[0007] The present invention provides Bi2O3—ZnO—Ta2O5 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.

[0008] Compounds within the compositional space defined by vertices A, B and C of the Bi2O3—ZnO—Ta2O5 system shown in FIG. 1 are produced. These compounds are illustrated by Bi2(ZnTa2)xO6x+3 where 0.57≦x≦1.0, by Bi2(ZnTay)⅔O((5y+11)/3) where 1.0≦y≦3.0, as well as by Bi2(ZnTay)⅔O((5y+11)/3) where 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, 0.125 mol % ZnO, 0.75 mol % Bi2O3; vertex B is defined by 0.125 mol % Ta2O5, 0.75 mol % ZnO, 0.125 mol % Bi2O3; and vertex C is defined by 0.6875 mol % Ta2O5, 0.125 mol % ZnO, 0.1875 mol % Bi2O3.

[0009] 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(Bi2(Zn⅓Ta⅔)2O7)-((1−r)(Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 ) ) where 0<r<1, also are produced.

[0010] 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)⅔O7, may be added to the compound.

[0011] The Bi2O3—ZnO—Ta2O5 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 δ<0.003) such as a tan δ<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

[0012] In a first embodiment, compounds of Bi2(ZnTa2)xO6x+3 where 0.57≦x≦1.0, of Bi2(ZnTay)⅔O((5y+11)/3) where 1.0≦y≦3.0 and of Bi2(ZnTay)⅔O((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

[0013] In manufacture of compounds of the formula Bi2(ZnTa2)xO6x+3, ZnO and Ta2O5 are reacted at 1000° C. to produce (ZnTa2)xO6x according to equation (1):

x (ZnO)+x(Ta2O5)→(ZnTa2)xO6x  (1)

[0014] The (ZnTa2)xO6x then is reacted at 1000° C. with Bi2O3 according to equation (1A) to produce a compound corresponding to Bi2(ZnTa2)xO6x+3:

Bi2O3+(ZnTa2)xO6x→Bi2(ZnTa2)xO6x+3  (1A)

[0015] In manufacture of (ZnTa2)xO6x, reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and reagent grade Ta2O5 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 (ZnTa2O6)x.

[0016] Bi2O3 is mixed with the (ZnTa2O6)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.

[0017] In manufacture of compounds of the formula Bi2(ZnTay)⅔O((5y+11)/3), ZnO and Ta2O5 are reacted at 1000° C. to produce (ZnTay)2O5y+2 according to equation (2):

2ZnO+yTa2O5→(ZnTay)2O5y+2  (2)

[0018] The (ZnTay)2O5y+2 then is reacted with 3Bi2O3 according to equation (2A) at 950-1100° C. to produce a compound corresponding to Bi2 (ZnTay)⅔O((5y+11)/3):

⅓(ZnTay)2O5y+2+Bi2O3→Bi2(ZnTay)⅔O((5y+11)/3)  (2A)

[0019] In manufacture of (ZnTay)2O5y+2, reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and reagent grade Ta2O5 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.

[0020] Bi2O3 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.

[0021] 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
	Reactant oxides	Final Compounds
			Ta2O5	ZnO	Bi2O3	Sintering	Ta2O5	Ta2O5	ZnO	ZnO	Bi2O3	Bi2O3
Ex.	x	y	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	10	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	1000	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

[0022] In a second embodiment, composites and solid solutions of the formula r(Bi2 (Zn⅓Ta⅔)2O7)-((1−r) (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7), 0<r<1, are produced as the reaction products of mixtures of Bi2(Zn⅓Ta⅔)2O7 and (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7.

[0023] To illustrate, a series of mixtures of Bi2(Zn⅓Ta⅔)2O7 (r=1) and (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 (r=0) powders are prepared according to the formula r(Bi2(Zn⅓Ta⅔)2O7)-((1−r) (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})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.

[0024] The Bi2(Zn⅓Ta⅔)2O7 and the (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 employed in examples 15-23 are produced as described below.

[0025] Manufacture of Bi2 (Zn⅓Ta⅔)2O7

[0026] 15.55 gms. of reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and 84.45 gms. of reagent grade Ta2O5 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 ZnTa2O6.

[0027] 57.19 gms. Bi2O3 are mixed with 42.81 gms. of the ZnTa2O6 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(Zn⅓Ta⅔)2O7 that measures 10 mm diameter and 1 mm thick.

[0028] Manufacture of (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7

[0029] 15.55 gms. of reagent grade ZnO of 99.9% purity from Aldrich Chemical Co. and 84.45 gms. of reagent grade Ta2O5 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 ZnTa2O6.

[0030] 45.85 gms. Bi2O3 and 2.67 gms. ZnO are mixed with the 51.48 gms. ZnTa2O6. 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 (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 that measures 10 mm diameter and 1 mm thick.

[0031] In manufacture of the Bi2(Zn⅓Ta⅔)2O7 and (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 compounds as described above, reagent grade oxides of Bi2O3, ZnO and Ta2O5 of 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

[0032] In another aspect, the Bi2 (Zn⅓Ta⅔)2O7 and (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 compounds each may be mixed with glass such as a P2O5 type glass, a PbO type glass, and a Bi2O3 type 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. %.

[0033] To illustrate, a borosilicate glass of the composition ZnO—B2O3—SiO2 is added to Bi2(Zn⅓Ta⅔)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.

[0034] The sintering temperatures of various blends of Bi2(Zn⅓Ta⅔)2O7 and the ZnO—B2O3—SiO2 borosilicate glass of composition 60 wt. % ZnO—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(Zn⅓Ta⅔)2O7 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.	1050	850	800	780
	*Based on weight of Bi2(Zn⅓Ta⅔)2O7

[0035] Reacted blends of Bi2(Zn⅓Ta⅔)2O7 and glass, (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 and glass, as well as mixtures thereof, also may be used to prepare solid solutions and composites as in the manner described above.

[0036] Dielectric Property Measurement

[0037] 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(Zn⅓Ta⅔)2O7, sintered Bi2(Zn⅓Ta⅔)2O7 with glass, sintered(Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7, as well as sintered solid solutions of Bi2(Zn⅓Ta⅔)2O7 and (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7 are measured.

[0038] Measurement of dielectric properties such as (K, tan δ and TCC) at low frequencies of 1 KHz to 1 MHz 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, Calif. 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.

[0039] 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 δ and TCC) at high frequencies of 400 MHz 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.

[0040] The measured properties are shown in Tables 3 to 7.

TABLE 3
Room Temperature K, Q and
TCC at 1 K 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	56	332.1
2	0.667	61.1	1053	39.5	60.8	1600	43.2	60.2	519	72.3	60.2	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	.645	62.8	4000	54.9	62.9	4000	57.7	64.9	476	87.7	63.1	131	165.4
12	.656	61.9	4444	50.5	61.9	4000	55.5	64.0	404	75.9	62.0	185	126.4
13	.678	47.7	1177	4.4	61.6	1026	24.0	63.0	1212	38.2	61.8	1143	41.3
14	.690	29.9	1667	−0.9	42.3	1177	11.2	62.9	1250	26.1	59.0	1177	61.7

[0041]

TABLE 4
Dielectric Properties at Room Temperature, at 1 MHz
Exam-		Sintering	Sintering
ple	r	Temp. ° C.	Time Hr.	K	tan δ	TCC
15	0	1000	4	71.4	<0.005	−172 ppm/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

[0042]

TABLE 5
K at 1 MHz 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	78.6	77.8	77.3	76.7	76.1
17	0.3	76.7	78.0	77.8	77.1	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

[0043]

TABLE 6
K at 10 KHz 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	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	77.2	76.9	76.2	75.1	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	68.7	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

[0044]

TABLE 7
tan δ at 1 MHz over the range of
−160° C. 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

Claims

1. A bismuth pyrochlore microwave dielectric compound of the formula Bi2(ZnTa2)xO6x+3 where 0.57≦x≦1.0.

2. A bismuth pyrochlore microwave dielectric compound of the formula Bi2(ZnTa2)xO6x+3 where x=0.57.

3. A bismuth pyrochlore microwave dielectric compound of the formula Bi2(ZnTa2)xO6x+3 where x=0.667.

4. The bismuth pyrochlore microwave dielectric compound of the formula Bi2(ZnTa2)xO6x+3 where x=0.80.

5. A bismuth pyrochlore microwave dielectric compound of the formula Bi2(ZnTay)⅔O((5y+11)/3) where 1.0≦y≦3.0.

6. A bismuth pyrochlore microwave dielectric compound of claim 5 where y=1.0

7. A bismuth pyrochlore microwave dielectric compound of claim 5 where y=1.5

8. A bismuth pyrochlore microwave dielectric compound of claim 5 where y=2.0

9. A bismuth pyrochlore microwave dielectric compound of claim 5 where y=2.5

10. A bismuth pyrochlore microwave dielectric compound of claim 5 where y=3.0

11. A bismuth pyrochlore microwave dielectric compound of the formula Bi2(ZnTay)⅔O((5y+11)/3) where 1.0≦y≦3.0, provided that y is not 2.0.

12. A bismuth pyrochlore microwave dielectric compound according to the formula r(Bi2(Zn⅓Ta⅔)2O7)-((1−r) (Bi{fraction (3/2)}Zn½) (Zn½Ta{fraction (3/2)})O7)) where 0<r<1.

13. The bismuth pyrochlore microwave dielectric compound according to claim 12 where r=0.2

14. The bismuth pyrochlore microwave dielectric compound according to claim 12 where r=0.3.

15. The bismuth pyrochlore microwave dielectric compound according to claim 12 where r=0.4.

16. The bismuth pyrochlore microwave dielectric compound according to claim 12 where r=0.5.

17. The bismuth pyrochlore microwave dielectric compound according to claim 12 where r=0.6.

18. The bismuth pyrochlore microwave dielectric compound according to claim 12 where r=0.85.

19. A bismuth pyrochlore microwave dielectric compound that is reaction product of a borosilicate glass and Bi2(ZnTa)⅔O7.

20. The bismuth pyrochlore microwave dielectric compound of claim 19 wherein the borosilicate glass is about 5 wt. % of the Bi2(ZnTa)⅔O7.

21. The bismuth pyrochlore microwave dielectric compound of claim 20 wherein the glass is a ZnO—B2O3—SiO2 glass.