# Patent

## Title
Microwave dielectric ceramic

## Abstract

A dielectric ceramic material consisting essentially of a composition of Formula 1

xATiO3(1−x)NdzRe(1−z)AlO3   (1)

doped with 0.005% to 5% of a dopant selected from the group consisting of: cerium oxide, manganese oxide and mixtures thereof;

wherein A may be selected from the group consisting of: Ca, Sr, Mg and mixtures thereof;

Re may be selected from a group consisting of La, Sm, Pr, Dy, Er, Gd, Y and mixtures thereof;

wherein z is from 0.95 to 0.995; and

wherein x is a positive number less than 1.

## Background
This application claims priority under 35 U.S.C. §119 to the following United Kingdom patent applications: No. 0516421.5, filed Aug. 10, 2005; No. 0518736.4, filed Sep. 14, 2005; and No. 0519804.9, filed Sep. 29, 2005.
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 consisting essentially of a composition of Formula 1:

xATiO3+(1−x)NdzRe(1−z)AlO3  (1)

doped with about 0.005 wt % to about 5 wt % of a dopant selected from the group consisting of: cerium oxide, manganese oxide and mixtures thereof;

wherein A may be selected from the group consisting of: Ca, Sr, Mg and mixtures thereof;

Re may be selected from a group consisting of La, Sm, Pr, Dy, Gd, Y, Er and mixtures thereof;

wherein z is from 0.95 to 0.995; and

wherein x is a positive number less than 1.

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 εr and TCf values while retaining Q values>10,000 at about 2 GHz suitable for their intended applications.
Preferred materials in accordance with this invention possess high relative permittivity εr values in comparison to known materials with equivalent Q values. Particularly preferred materials have εr of 42-50, Q>10,000, for example>14,000, at about 2 GHz (e.g., 2.7 GHz) and TCf between −10 to +10 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:

xCadSr(1−d)TiO3+(1−x)NdzRe(1−z)AlO3  (2)

    
    
        doped with about 0.005% to about 5% of a dopant selected from the group consisting of: cerium oxide, manganese oxide and mixtures thereof;
        
            wherein 0.5≦x≦0.9
            
                0.25≦d≦1.0
                0.95≦z≦0.995
                1≦y≦2
                Re may be selected from a group consisting of La, Sm, Pr, Dy and mixtures thereof and wherein
                CeO2 is added as a dopant in the range about 50 ppm to about 2.5 wt %.
                MnOy is added as a dopant in the range about 50 ppm to about 2.5 wt %.
            
            
        
        
    
    


Further preferred materials consist essentially of a composition of Formula 3:

xCaTi1.03O3+(1−x)Nd0.95Re0.05AlO3  (3)

    
    
        wherein 0.65≦x≦0.72; y and Re are as stated above and wherein
        CeO2 is added as a dopant in the range about 50 ppm to about 2.0 wt %.
        MnOy is added as a dopant in the range about 50 ppm to about 1.0 wt %.
        In preferred materials the ratio of Nd:Re is about 19:1.
    
    


An additional dopant selected from Fe2O3, Nb2O5, Ta2O5, Ga2O3 and mixtures thereof preferably Ga2O3 may be present in an amount of about 20 to about 5000 ppm, more preferably about 20 to about 2000 ppm.
The manganese oxide may be provided as the oxide or mixture of oxides or as a carbonate, oxalate or other thermally labile derivative.
The Ca, Nd, Al, Ti site occupancies may all be varied by +/−10%. In this specification MnOy refers to the material after firing. Most Mn salts may be used to achieve the final MnOy.
The electrical properties for these ceramics can be summarised as follows:

εr42−48

    
    
        Q (2 GHz)>10,000
        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.
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 yttria stabilised 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 1100° C. to 1400° C. for 1 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 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 TE016 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. Er measurements were made using the parallel plate transmission technique of Hakki and Coleman.


EXAMPLE 1
Data mixtures of CaTiO3 (CT) and Nd0.95Sm0.05AlO3 (NSA); i.e a ratio of Nd to Sm of 19:1—aiming for a TCf between +6 and −6 MK−1 were as shown in Table 1.













TABLE 1





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





















0.700 CT + 0.300 NSA
4.79
2.67
46.8
15300
40700
5.6


0.695 CT + 0.305 NSA
4.78
2.69
46.0
15300
41000
3.3


0.690 CT + 0.310 NSA
4.81
2.70
46.7
15300
41200
0.8


0.685 CT + 0.315 NSA
4.80
2.72
44.9
15300
41400
−1.5


0.680 CT + 0.320 NSA
4.83
2.74
45.3
15100
41400
−4.0









EXAMPLE 2
Variation in electrical properties as a function of Nd to auxiliary rare earth ratio: Properties of undoped CTNReA (0.700 CaTi1.03O3+0.300 Nd0.9Re0.1AlO3) ceramics where the ratio of Nd to Re is equal to 9:1 are shown in Table 2.













TABLE 2






Density/







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







100% Nd2O3
4.77
2.67
46.6
15500
41400
6.0







Substitution of alternative rare earth for Nd in a ratio 10:1













CeO2
4.76
2.65
46.9
14700
39000
7.9


Sm2O3
4.77
2.68
46.6
15600
41600
6.1


Pr6O11
4.76
2.66
47.0
15500
41200
8.3


Dy2O3
4.78
2.68
46.4
14000
37400
6.8


Y2O3
4.71
2.68
46.2
14100
37700
5.3









EXAMPLE 3
Properties of undoped CTNReA (0.700 CaTi1.03O3+0.300 Nd0.95Re0.05AlO3) ceramics where the ratio of Nd to Re is equal to 19:1 are shown in Table 3.













TABLE 3






Density/







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







100% Nd2O3
4.77
2.67
46.6
15500
41400
6.0







Substitution of alternative rare earth for Nd in a ratio 19:1













La2O3
4.74
2.66
46.9
15300
40700
6.6


Sm2O3
4.75
2.67
46.6
15300
40600
6.1


Pr6O11
4.75
2.66
46.9
15300
40700
6.9









EXAMPLE 4
Properties of doped CTNReA (0.690 CaTi1.03O3+0.310 [Nd,Sm]AlO3+0.5 wt % CeO2) ceramics where the ratio of Nd to Sm is greater than 19:1 are shown in Table 4.













TABLE 4





Nd:Sm
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







99:1
4.80
2.70
45.3
15800
42600
−0.6


49:1
4.79
2.71
45.4
15800
42800
−0.6


32:1
4.80
2.70
45.4
15700
42400
−0.2


24:1
4.80
2.71
45.3
15900
43000
−1.0


19:1
4.80
2.73
45.4
15500
42100
−0.5









EXAMPLE 5
Properties of undoped CTNReA (0.700 CaTi1.03O3+0.300 Nd0.05Re0.95AlO3) ceramics where the ratio of Nd to Re is equal to 1:19 are shown in Table 5.













TABLE 5






Density/







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





















100% Nd2O3
4.77
2.67
46.6
15500
41400
6.0







Substitution of alternative rare earth for Nd in a ratio 1:19













La2O3
4.65
2.57
49.9
14000
35850
22.0


Sm2O3
4.81
2.69
45.7
15200
40900
7.9


Pr6O11
4.68
2.60
48.8
14300
37200
24.9









EXAMPLE 6
Properties of undoped CTNPrA (0.660 CaTi1.03O3+0.340 [Nd,Pr]AlO3) ceramics where the ratio of Nd to Pr is varied for zero TCf are shown in Table 6.













TABLE 6





Nd:Pr
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















1:19.0
4.84
2.76
44.0
14500
39800
1.1


1:18.0
4.80
2.73
44.8
14100
38500
6.6


1:17.0
4.76
2.70
45.7
13900
37400
13.0


1:16.0
4.72
2.66
46.8
13400
35700
20.0


1:15.5
4.70
2.65
47.5
12900
34200
25.5









EXAMPLE 7
Single doping of zero TCf material where Nd:Sm is 19:1.
Base material: 0.690 CaTi1.03O3+0.310 Nd0.95Sm0.05AlO3 
The data for MnO2 doping are shown in Table 7(a)













TABLE 7(a)






Density/







wt % MnO2
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







0.000
4.79
2.70
45.7
15300
41200
0.8


0.005
4.78
2.71
45.7
15300
41500
1.0


0.010
4.78
2.70
45.7
15400
41500
0.9


0.050
4.78
2.70
45.7
15000
40400
0.9


0.100
4.78
2.70
45.7
15000
40400
1.0


0.250
4.78
2.70
45.7
14200
38400
0.9









The data for CeO2 doping are shown in Table 7(b)













TABLE 7(b)






Density/







wt % CeO2
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















0.000
4.79
2.70
45.7
15300
41200
0.8


0.005
4.79
2.70
45.7
15600
42200
0.8


0.010
4.80
2.71
45.4
15600
42200
0.8


0.050
4.81
2.70
45.5
15700
42400
0.7


0.100
4.80
2.71
45.4
15600
42400
0.4


0.200
4.79
2.70
45.3
15700
42400
0.1


0.500
4.81
2.71
45.2
15700
42500
−0.7









The data for Co-doping with CeO2 & MnO2 are shown in Table 7(c)













TABLE 7(c)





wt % CeO2 &
Density/







% MnO2
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







0.00 & 0.00
4.79
2.70
45.7
15300
41200
0.8


0.01 & 0.01
4.78
2.70
45.5
15300
41200
0.8


0.03 & 0.03
4.78
2.70
45.5
15200
41100
0.8


0.05 & 0.05
4.78
2.70
45.6
15200
40900
0.8


0.01 & 0.05
4.78
2.69
45.5
15300
41300
0.8


0.05 & 0.01
4.78
2.70
45.6
15100
40700
1.0









EXAMPLE 8
Single doping of zero TCf material where Nd:Sm or Nd:Pr is 1:19.
Base material: 0.690 CaTi1.03O3+0.310 Nc0.05Sm0.95AlO3 













TABLE 8(a)






Density/







wt % CeO2
g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







0.0
4.86
2.73
44.6
15400
42100
2.8


0.1
4.86
2.74
44.6
15300
41700
2.8


0.2
4.85
2.74
44.4
15400
42100
2.3


0.5
4.86
2.75
44.3
15500
42400
1.5









Base material: 0.660 CaTi1.03O3+0.340 Nd0.05Pr0.95AlO3 













TABLE 8(b)





wt %








CeO2
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















0.0
4.84
2.76
44.0
14500
39800
1.1


0.1
4.82
2.76
43.9
14400
39800
0.6


0.5
4.83
2.76
43.7
14500
40000
0.7









EXAMPLE 9
Additional doping trials:
(a) Fe2O3 
Fe2O3 was added as an excess to the composition 0.690 CaTi1.03O3+0.310 Nd0.95Sm0.05AlO3.













TABLE 9(a)





wt %








Fe2O3
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1





















0.000
4.79
2.70
45.7
15300
41200
0.8


0.005
4.77
2.69
45.7
15500
41700
1.2


0.010
4.77
2.69
45.7
15500
41700
1.3


0.050
4.77
2.69
45.7
15300
41100
1.5


0.100
4.78
2.69
45.7
15100
40500
1.6


0.500
4.77
2.69
45.8
13400
36200
2.3









(b) SrO

SrO was added as a substitution for Ca in the composition 0.690 (Ca,Sr)Ti1.03O3+0.310 Nd0.95Sm0.05AlO3+0.2 wt % excess CeO2.












TABLE 9(b)





mol % SrO
Density/g cm−3
f/GHz
εr
Q
Qf/GHz




















0.0
4.79
2.70
45.7
15300
41200


1.0
4.77
2.69
45.9
14900
40200


2.0
4.79
2.69
45.9
15100
40500


5.0
4.82
2.70
46.1
14500
39200


10.0
4.86
2.68
46.7
14100
37800


20.0
4.93
2.67
47.6
12700
34000









(c) Nb2O5 

Nb2O5 was added an excess to the composition 0.690 CaTi1.03O3+0.310 Nd0.95Sm0.05AlO3 
+0.2 wt % excess CeO2.













TABLE 9(c)





wt %








Nb2O5
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







0.0
4.79
2.70
45.7
15300
41200
0.8


0.1
4.77
2.70
45.7
15600
42100
1.2


0.2
4.77
2.70
45.7
15600
42000
1.3


0.5
4.77
2.70
45.9
15300
41200
1.5









(d) Ta2O5 

Ta2O5 was added an excess to the composition 0.690 CaTi1.03O3+0.310 Nd0.95Sm0.05AlO3 
+0.2 wt % excess CeO2.













TABLE 9(d)





wt %








Ta2O5
Density/g cm−3
f/GHz
εr
Q
Qf/GHz
TCf/MK−1







0.0
4.79
2.70
45.7
15300
41200
0.8


0.1
4.78
2.71
45.6
15600
42300
1.0


0.2
4.78
2.69
45.7
15600
41900
1.2


0.5
4.78
2.70
45.7
15700
42500
1.1









(e) Ga2O3 

Ga2O3 was added as both an excess and a substitute for Ti in the composition 0.690 CaTi1.03O3+0.310 Nc0.95Sm0.05AlO3+0.2 wt % excess CeO2.













TABLE 9(e)






Density/




TCf/


% Ga2O3
g cm−3
f/GHz
εr
Q
Qf/GHz
MK−1





















0.000
4.79
2.70
45.7
15300
41200
0.8


0.005 on Ti site
4.77
2.70
45.4
16100
43500
−0.1


0.010 on Ti site
4.77
2.70
45.1
16200
43800
−0.8


0.100 wt % excess
4.77
2.70
45.6
15900
42700
1.0


0.200 wt % excess
4.77
2.69
45.7
15900
42700
1.1


0.500 wt % excess
4.77
2.69
45.6
15700
42200
1.5









EXAMPLE 10
Influence of cation stoichiometry upon electrical properties:
(a) Ca
The composition range examined was 0.690 CazTi1.03O3+0.310 Nd0.95Sm0.05AlO3+0.2 wt % excess CeO2, where z varied between 0.95 and 1.05.













TABLE 10(a)





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





















0.95
4.78
2.67
46.8
14000
37400
6.8


0.97
4.78
2.68
46.4
14500
38800
4.4


0.99
4.78
2.69
46.0
15100
40700
1.9


1.00
4.79
2.70
45.7
15300
41200
0.8


1.01
4.77
2.71
45.2
15600
42100
−0.7


1.03
4.61
2.76
42.5
12600
34700
−2.0


1.05
4.74
2.74
44.2
14700
40300
−4.7









(b) Ti

The composition range examined was 0.690 CaTizO3+0.310 Nd0.95Sm0.05AlO3+0.2 wt %
excess CeO2, where z varied between 0.98 and 1.08.













TABLE 10(b)





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





















0.98
4.76
2.78
43.0
14400
40000
−9.7


1.00
4.69
2.78
42.9
12400
34300
−5.3


1.02
4.78
2.72
45.1
15500
42200
−1.5


1.03
4.79
2.70
45.7
15300
41200
0.8


1.04
4.78
2.70
46.2
15100
40600
2.9


1.06
4.78
2.66
47.0
14500
38400
7.6


1.08
4.79
2.64
48.0
13900
36500
12.2









(c) Al

The composition examined was 0.690 CaTi1.03O3+0.310 Nd0.95Sm0.05AlzO3+0.2 wt % excess CeO2, where z varied between 0.95 and 1.05.













TABLE 10(c)





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





















0.95
4.46
NR
—
—
—
—


0.97
4.78
2.70
45.7
15400
41500
0.4


0.99
4.78
2.70
45.6
15600
41900
0.4


1.00
4.79
2.70
45.7
15300
41200
0.8


1.01
4.78
2.70
45.6
15400
41600
0.7


1.03
4.78
2.70
45.6
15400
41400
1.1


1.05
4.78
2.71
45.5
15100
40800
1.4





NR—no resonance detected






EXAMPLE 11
1 and 2 GHz parts:
Commercial size resonators were developed from the following composition:

0.69CaTi1.03O3+0.31Nd0.95Sm0.05AlO3+0.2 wt % excess CeO2.   Comp A

The electrical response of ceramics prepared from the above composition A were evaluated against an undoped material of composition:

0.69CaTi1.03O3+0.31NdAlO3  Comp B

The measured Q-values were as follows:












TABLE 11







Freq/GHz
Comp A
Comp B
% Differential









1.0
34600
33000
4.6



2.0
21000
20300
3.3



2.7
16000
15600
2.5










EXAMPLE 12
Dopant and influence on Q-value at elevated temperatures:

    
    
        Composition: Comparison of Q-value at ambient and elevated temperature for compositions A and B (0.69 CaTi1.03O3+0.31 Nd0.95Sm0.05AlO3)
    
    











TABLE 12





Temperature/′′ C.
Q-value of Comp A
Q-value of Comp B

















22
16000
15600


80
13900
13500


120
12800
12400


150
12000
11600









Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the compositions of the present invention. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
The entire disclosures of all references cited herein are incorporated by reference for all purposes.

## Claims

1. A dielectric ceramic material consisting essentially of a composition of formula 1:


xATiO3+(1−x)NdzRe(1−z)AlO3  (1)


doped with about 0.005% to about 5% of a dopant selected from the group consisting of:
CeO2, MnOy and mixtures thereof;
wherein A is selected from the group consisting of: Ca, Sr, Mg and mixtures thereof;
Re is selected from a group consisting of La, Sm, Pr, Dy, Gd, Y, Er and mixtures thereof;
wherein z is from 0.95 to 0.995;
wherein x is a positive number less than 1 and 1≦y≦2.

2. A dielectric ceramic material as claimed in claim 1 with a composition of formula 2:


xCadSr(1−d)TiO3+(1−x)NdzRe(1−z)AlO3  (2)


doped with about 0.005% to about 5% of a dopant selected from the group consisting of:
CeO2, MnOy and mixtures thereof;
wherein 0.5≦x≦0.9
0.25≦d≦1.0
0.95≦z≦0.995
1≦y≦2
Re is selected from a group consisting of La, Sm, Pr, Dy, Gd, Y, Er and
mixtures hereof and wherein
CeO2 is added as a dopant in the range about 50 ppm to about 2.5 wt %.
MnOy is added as a dopant in the range about 50 ppm to about 2.5 wt %.

3. A dielectric ceramic material as claimed in claim 1 with a composition of formula 3:


xCaTi1.03O3+(1−x)Nd0.95Re0.05AlO3  (3)

wherein 0.60≦x≦0.72 and y are as stated above and Re is Sm or Pr and wherein
CeO2 is added as a dopant in the range about 50 ppm to about 2.5 wt %, and
MnOy is added as a dopant in the range about 50 ppm to about 2.5 wt %.

4. A dielectric ceramic material as claimed in claim 3,
wherein 0.65≦x≦0.72, Re is Sm
and CeO2 is added as an excess dopant in an amount of 0.2 wt %.

5. A dielectric ceramic material as claimed in claim 1 with a composition of formula 4:


xCaTi1.03O3+(1−x)Nd0.05Re0.95AlO3  (4)

wherein 0.60≦x≦0.72 and y are as stated above and Re is Sm or Pr and wherein
CeO2 is added as a dopant in the range about 50 ppm to about 2.5 wt %, and
MnOy is added as a dopant in the range about 50 ppm to about 2.5 wt %.

6. A dielectric ceramic material as claimed in claim 5,
wherein 0.60≦x≦0.72, Re is Sm
and CeO2 is added as an excess dopant in an amount of from 0.01 wt % to 1.0 wt %.

7. A dielectric ceramic material as claimed in claim 5,
wherein 0.60≦x≦0.72: Re is Pr
and CeO2 is added as an excess dopant in an amount of from 0.01 wt % to 1.0 wt %.

8. A dielectric ceramic material as claimed in claim 3 wherein Sr, Mg or a mixture thereof are substituted for Ca in an amount of 0 to 20 mol % and wherein 0.85≦x≦1.0.

9. A dielectric ceramic material as claimed in claim 1, further comprising an additional dopant in an amount of 20 to 5000 ppm, wherein the additional dopant is selected from the group consisting of: Fe2O3, Nb2O5, Ta2O5, Ga2O3 and mixtures thereof.

10. A dielectric ceramic material as claimed in any preceding claim 2, including further comprising an additional dopant in an amount of 20 to 5000 ppm, wherein the additional dopant is selected from the group consisting of: Fe2O3, Nb2O5, Ta2O5, Ga2O3 and mixture thereof.

11. A dielectric ceramic material as claimed in any preceding claim 3, including further comprising an additional dopant in an amount of 20 to 5000 ppm, wherein the additional dopant is selected from the group consisting of: Fe2O3, Nb2O5, Ta2O5, Ga2O3 and mixture thereof.

12. A dielectric ceramic material as claimed in claim 9, wherein the additional dopant is Ga2O3.

13. A dielectric ceramic material as claimed in claim 12, wherein the amount of Ga2O3 is from 20 to 2000 ppm.

14. A dielectric ceramic material as claimed in claim 3, wherein the cation site occupancy of Ca, Ti, Nd and Al is varied by ±10%.

15. A dielectric ceramic material as claimed in claim 1, wherein the material has electrical properties summarised as follows:


εr42−48

Q (2 GHz)>10,000
TCf (variable through composition)−10 to +10 MK−1.

16. A dielectric ceramic material as claimed in claim 1, wherein the material has electrical properties summarised as follows:


εr42−48

Q (2.7 GHz)>14,000
TCf (variable through composition)−10 to +10 MK−1.

17. A dielectric resonator comprising a dielectric ceramic material as claimed in claim 1.

18. A dielectric resonator as claimed in claim 17 with a composition of formula 2.

19. A dielectric resonator as claimed in claim 17 with a composition of formula 3.

20. A dialectic resonator as claimed in claim 17, wherein the dielectric ceramic material has electrical properties summarised as follows:


εr42−48

Q (2 GHz)>10,000
TCf (variable through composition)−10 to +10 MK−1.