Microwave dielectric ceramic

Information

  • Patent Grant
  • 7732362
  • Patent Number
    7,732,362
  • Date Filed
    Tuesday, December 18, 2007
    17 years ago
  • Date Issued
    Tuesday, June 8, 2010
    14 years ago
Abstract
A dielectric ceramic material as claimed in claim 1 with a composition of formula x CaTiO3+(1−x)SmzRe(1−z)AlO3  (1)optionally doped with about 0.005% to about 5% of CeO2 as a dopant, wherein 0.5≦x≦0.9,0.3≦z≦0.995, orRe may be selected from a group consisting of La, Pr, Dy, Gd, Y, Er, Ho and mixtures thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of U.K. Patent Application No. 0700265.2, filed on Jan. 8, 2007, which is hereby incorporated by reference.


This invention relates to a dielectric ceramic material and also to a dielectric resonator comprising the novel ceramic material, the resonator being particularly useful for microwave application.


According to the present invention there is provided a dielectric ceramic material with a composition of Formula (1)

x CaTiO3+(1−x)SmzRe(1−z)AlO3  (1)

    • wherein 0.5≦x≦0.9
      • 0.3≦z≦0.995
      • Re may be selected from a group consisting of La, Pr, Dy, Gd, Y, Er, Ho and mixtures thereof.


Materials in accordance with this invention find application in microwave base station filters (single and multimode). Preferred materials may be prepared which allow changes to relative permittivity ∈r and TCf values while retaining Q values >10,000 at 2 GHz suitable for their intended applications. Materials of this invention may yield superior dielectric loss characteristics in comparison to prior art compositions. They are also relatively economical to manufacture.


Preferred materials in accordance with this invention possess high relative permittivity ∈r values in comparison to known materials with equivalent Q values. Particularly preferred materials have ∈r of 40-50, Q>10000 at 2 GHz (Qf>20000 GHz) and TCf between −20 to +20 MK−1


Materials in accordance with this invention possess further advantages in relation to materials disclosed in the prior art, for example U.S. Pat. No. 5,356,844, because the ceramics of this invention have an improved microwave quality factor at ambient and higher operating temperatures.


Preferred materials consist essentially of a composition of Formula 2

x CaTi1.03O3+(1−x)Sm0.95Y0.05AlO3  (2)

    • wherein 0.65≦x≦0.72


Further preferred materials consist essentially of a composition of Formula 3

x CaTi1.03O3+(1−x)Sm0.8Y0.2AlO3  (3)

    • wherein 0.65≦x≦0.72


In further preferred materials, Re consists essentially of a composition of two or more elements selected from the group consisting of: La, Nd, Pr, Dy, Gd, Y, Er and Ho.


A dopant selected from CeO2, Fe2O3, MnO2, Nb2O5, Ta2O5, Ga2O3 and mixtures thereof. The dopant may be present in an amount of about 20 to about 5000 ppm, more preferably about 20 to about 1000 ppm.


CeO2 where present may be added as a dopant in the range about 50 ppm to about 2.0 wt %.


The Ca, Al, Ti or Re site occupancies may all be varied by +/−10%.


The electrical properties for these ceramics can be summarised as follows:

    • r 40-50
    • Q (2 GHz)>10000
    • TCf(variable through composition) −10 to +10 MK−1


Compositions of the present invention may be manufactured by mixing the appropriate oxides, carbonates or oxalates or mixtures thereof in the above mentioned proportions, pulverising the mixture using a wet or dry method, calcining the mixture at a temperature of 1100° C. to 1400° C. for 1 to 16 hours, shaping the calcined mixture into an optional form and sintering the shaped body at a temperature of 1400° C. to 1700° C.


Percentages and other amounts referred to in this specification are by weight unless indicated otherwise. Percentages and other proportions are selected from the ranges specified to total 100%.


The invention is further described by means of example but not in any limitative sense;







EXPERIMENTAL PROCEDURE

All initial starting powders were of purity >99%. The raw materials were weighed in the appropriate quantities to form the compositions required. Deionised water or propan-2-ol was added to the weighed batches which were subsequently ball milled with magnesia stabilised zirconia milling media for 16 hours. Alternatively, the materials were attrition milled for 2 hours with zirconia media. Subsequently, the raw material batches were dried at 80° C. and sieved through a 250 μm nylon mesh. The dried powder was calcined at temperatures in the interval 1150° C. to 1350° C. for 2 to 16 hours. The as-calcined powders were re-milled with 2 wt % PEG binder (MW 10000) for 8 hours, dried and sieved. Standard test samples of 9.2 g weight were uniaxially pressed in a 20 mm hardened stainless steel die using a pressure of ˜150 MPa. Sintering of the pellets was performed between 1350 and 1600° C. for 1 to 48 hours under either an air or oxygen atmosphere. All samples were of density >95% theoretical density using the Archimedes water immersion technique.


The electrical properties were tested on the sintered components. Microwave dielectric properties were measured in reflection using the TE0Iδ mode in a cubic silver plated cavity. TCf measurements were made in the interval +80° C. to −20° C. with the values of 60, 20 and −10° C. being used to calculate TCf. ∈r measurements were made using the parallel plate transmission technique of Hakki and Coleman.


EXAMPLE 1
Molar Ratios Required for Useful TCf Materials

Data for mixtures of CaTiO3 (CT) and Sm0.95Y0.05AlO3 (SYA) plus 0.2 wt % CeO2 as excess, aiming for a TCf between +6 and −3 MK were as shown in Table 1:















TABLE 1





Material
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















0.69 CT-0.31 SA
4.84
2.72
44.5
16000
43500
2.3


 0.7 CT-0.3 SYA
4.80
2.68
45.2
15700
42000
6.4


0.69 CT-0.31 SYA
4.82
2.71
44.1
15700
42500
1.7


0.68 CT-0.32 SYA
4.86
2.75
43.1
15800
43200
−3.1





SA denotes SmAlO3.






Data for mixtures of CaTiO3 (CT) and Sm0.95Pr0.05AlO3 (SPA) plus 0.2 wt % CeO2 as excess, aiming for a TCf between +6 and −3 MK−1 were as shown in Table 2:















TABLE 2





Material
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















 0.7 CT-0.3 SPA
4.80
2.71
44.6
15600
41600
7.1


0.69 CT-0.31 SPA
4.83
2.67
44.4
15600
42300
2.3


0.68 CT-0.32 SPA
4.87
2.71
44.4
15800
43200
−2.6









Data for mixtures of CaTiO3 (CT) and Sm0.95Dy0.05AlO3 (SDA) plus 0.2 wt % CeO2 as excess, aiming for a TCf between +6 and −3 MK−1 were as shown in Table 3:















TABLE 3





Material
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















 0.7 CT-0.3 SDA
4.82
2.68
45.2
15400
41100
7.1


0.69 CT-0.31 SDA
4.85
2.71
44.3
15400
41600
2.2


0.68 CT-0.32 SDA
4.88
2.74
43.2
15500
42300
−2.3









Data for mixtures of CaTiO3 (CT) and Sm0.95Gd0.05AlO3 (SGA) plus 0.2 wt % CeO2 as excess, aiming for a TCf between +6 and −3 MK−1 were as shown in Table 4:















TABLE 4





Material
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















 0.7 CT-0.3 SGA
4.82
2.67
45.3
12500
33400
6.3


0.69 CT-0.31 SGA
4.85
2.71
44.2
12500
33700
1.6


0.68 CT-0.32 SGA
4.88
2.74
43.2
12500
34100
−3.1









The influence of the rare earth ion upon properties was summarised as shown in Table 5. Composition: 0.69 CaTiO3+0.31Sm0.95Re0.05AlO3 with 0.2 wt % excess CeO2















TABLE 5






Density/







Re
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







La2O3
4.82
2.71
44.7
15900
42900
2.7


Y2O3
4.82
2.71
44.1
15700
42500
1.7


Pr6O11
4.83
2.67
45.5
15600
42300
2.3


Dy2O3
4.85
2.71
44.3
15400
41600
2.2


Gd2O3
4.85
2.71
44.2
12500
33700
1.6









EXAMPLE 2
Influence of Rare Earth Ion Concentration Upon Dielectric Properties

The following data was generated for the composition:

0.69CaTiO3+0.31SmzRe(1−z)AlO3


Results using Y2O3 as a substituent for Sm2O3 are as shown in Table 6.















TABLE 6






Density/







z
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















1
4.84
2.72
44.5
16000
43500
2.3


0.99
4.83
2.72
44.5
16000
43400
2.4


0.975
4.82
2.72
44.4
16000
43500
2.3


0.95
4.80
2.72
44.3
16100
43700
2.2


0.9
4.77
2.72
44.2
16300
44400
1.7


0.8
4.72
2.72
43.8
16800
45600
1.1


0.6
4.62
2.73
43.0
17100
46600
−0.4


0.4
4.52
2.73
42.5
16800
45800
−1.4


0.2
4.40
2.75
39.1
7600
20800
−49.0


0
4.27
2.79
37.7
1200
3400









Results using Pr6O11 as a substituent for Sm2O3, with 0.2 wt % CeO2 as excess are shown in Table 7.















TABLE 7






Density/







z
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















1
4.84
2.72
44.5
16000
43500
2.3


0.95
4.83
2.71
44.4
15600
42300
2.3


0.9
4.83
2.70
41.6
15600
42000
2.7


0.85
4.83
2.69
41.6
15400
41500
3.2









Results using La2O3 as a substituent for Sm2O3 are shown in Table 8.















TABLE 8






Density/







z
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















1
4.84
2.72
44.5
16000
43500
2.3


0.99
4.82
2.72
44.5
16000
43500
2.4


0.975
4.82
2.71
44.5
16000
43200
2.4


0.95
4.82
2.71
44.7
15900
42900
2.7


0.9
4.81
2.70
44.9
15700
42300
3.1


0.8
4.81
2.69
45.4
15100
40600
4.3









EXAMPLE 3
Influence of Dopants Upon the Dielectric Properties

The following data was generated for the composition 0.69 CaTiO3+0.31 ReAlO3 as shown in Table 9.
















TABLE 9







Density/



Qf/
TCf/


Re
Dopant
g cm−3
f/GHz
εr
Q
GHz
MK−1







Sm0.8Y0.2
Nil
4.72
2.72
43.8
16800
45600
1.1


Sm0.8Y0.2
0.2 wt % CeO2 as excess
4.73
2.72
43.6
16500
44900
0.3


Sm0.95Y0.05
Nil
4.80
2.72
44.3
16100
43700
2.2


Sm0.95Y0.05
0.01 mol Ga2O3 on Ti site
4.82
2.74
43.6
15600
42700
0.4


Sm0.95Y0.05
0.2 wt % Ga2O3 as excess
4.83
2.72
44.4
15600
42400
2.4


Sm0.95Y0.05
0.2 wt % Fe2O3 as excess
4.83
2.71
44.5
15000
40800
2.6


Sm0.95Y0.05
0.2 wt % MnO2 as excess
4.83
2.71
44.3
14700
39900
2.0


Sm0.95Y0.05
0.2 wt % Ta2O5 as excess
4.84
2.72
44.4
15600
42500
2.1


Sm0.95Y0.05
0.2 wt % Nb2O5 as excess
4.83
2.71
44.6
15600
42300
2.2





All data is provisional and based upon non optimised dopant concentrations and firing conditions.






EXAMPLE 4
Sintering Time and Temperature Reduction

The following data was generated for the composition 0.69 CaTiO3+0.31 Sm0.8Y0.2AlO3 as shown in Table 10.















TABLE 10






Density/







Sinter T/t
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















1425/8
4.66
2.74
42.6
15800
43300
1.8


1450/8
4.73
2.72
43.9
16600
45100
1.4


1475/8
4.72
2.72
43.8
17000
46300
1.2


1500/8
4.72
2.72
43.8
16800
45600
1.1


1525/8
4.76
2.72
43.8
16400
44700
1.0


 1450/24
4.75
2.72
44.0
16800
45600
1.2


1500/2
4.70
2.72
43.4
16300
44500
1.3





where T denotes temperature in ° C. and t denotes time in hours






The following data was generated for the composition 0.69 CaTiO3+0.31 Nd0.95Sm0.95AlO3+0.2 wt % CeO2 as a comparison to the above as shown in Table 11.















TABLE 11






Density/







Sinter T/t
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







1425/8
4.78
2.68
45.5
15100
40400
1.8


1450/8
4.81
2.69
45.5
15500
41800
1.0


1475/8
4.81
2.69
45.5
15800
42400
0.9


1530/8
4.78
2.69
45.3
15700
42400
0.8





where T denotes temperature in ° C. and t denotes time in hours





Claims
  • 1. A dielectric ceramic material with a composition of Formula (1) x CaTiO3+(1−x)SmzRe(1−z)AlO3  (1)wherein 0.65≦x≦0.72 0.8≦z≦0.995Re is selected from the group consisting of La and Y and mixtures thereof.
  • 2. A dielectric ceramic material as claimed in claim 1 with a composition of Formula (2) x CaTi1.03O3+(1−x)Sm0.95Y0.05AlO3  (2)wherein 0.65≦x≦0.72.
  • 3. A dielectric ceramic material as claimed in claim 1 with a composition of formula (3) x CaTi1.03O3+(1−x) Sm0.8Y0.2AlO3  (3)wherein 0.65≦x≦0.72.
  • 4. A dielectric ceramic material as claimed in claim 1, wherein Sr, Mg or a mixture thereof are substituted for Ca in an amount of 0 to 20 mol %.
  • 5. A dielectric ceramic material as claimed in claim 1, including a dopant, wherein the dopant is selected from the group consisting of: CeO2, Nb2O5, Ga2O3, and mixtures thereof, wherein the total amount of dopant is from about 20 ppm to 2 wt %.
  • 6. A dielectric ceramic material as claimed in claim 5, wherein CeO2 is added as a dopant in the range about 50 ppm to about 2.0 wt %.
  • 7. A dielectic ceramic material as claimed in claim 1, wherein the cation site occupancy of Ca, Ti, Re and Al is varied by ±10%.
  • 8. A dielectric resonator comprising a dielectric ceramic material as claimed in claim 1.
Priority Claims (1)
Number Date Country Kind
0700265.2 Jan 2007 GB national
US Referenced Citations (7)
Number Name Date Kind
5401702 Kim et al. Mar 1995 A
6025291 Murakawa Feb 2000 A
6645896 Okamoto et al. Nov 2003 B2
6881694 Mizui et al. Apr 2005 B2
7326667 Iddles et al. Feb 2008 B2
20040029710 Mizui et al. Feb 2004 A1
20070035216 Iddles et al. Feb 2007 A1
Foreign Referenced Citations (3)
Number Date Country
1341189 Sep 2003 EP
11130544 May 1999 JP
2004182534 Jul 2004 JP
Related Publications (1)
Number Date Country
20080167176 A1 Jul 2008 US