Modified barium tungstate for co-firing
Disclosed herein are embodiments of low temperature co-fireable barium tungstate materials which can be used in combination with high dielectric materials, such as nickel zinc ferrite, to form composite structures, in particular for isolators and circulators for radiofrequency components. Embodiments of the material can include flux, such as bismuth vanadate, to reduce co-firing temperatures.
1. A composite material for use in radiofrequency applications, the composite material comprising:
a high magnetization spinel structure; and
a barium tungstate structure surrounding the high magnetization spinel structure, the barium tungstate structure doped with a flux material having a firing temperature the same as or lower than a firing temperature of the high magnetization spinel structure.
2. The composite material of claim 1 wherein the flux material comprises BiVO 4 .
3. The composite material of claim 2 wherein the flux material comprises 1-2 wt. % BiVO 4 .
4. The composite material of claim 1 wherein the flux material comprises 1-10 wt. % MgAl 2 O 4 or CoAl 2 O 4 .
5. The composite material of claim 1 wherein the barium tungstate is doped with BiVO 4 and one of MgAl 2 O 4 or CoAl 2 O 4 .
6. The composite material of claim 1 wherein the composite material has a fired density of greater than 5.10 g/cm 3 .
7. The composite material of claim 1 wherein the barium tungstate structure reduces in diameter around the high magnetization spinel structure during firing so that no adhesive is used to connect the barium tungstate structure with the high magnetization spinel structure.
8. The composite material of claim 1 wherein the composite material is defined by the formula Ba 1-x Bi x W 1-x V x O 4 .
9. The composite material of claim 1 wherein the barium tungstate and the flux material have a scheelite structure.
10. The composite material of claim 1 wherein the doped barium tungstate has a thermal expansion coefficient of about 9 ppm/° C.
11. The composite material of claim 1 wherein the high magnetization spinel structure has a dielectric constant of at least 30.
12. A method of forming a composite material, the method comprising:
providing a high magnetization spinel structure;
providing a barium tungstate outer structure, the barium tungstate outer structure being doped with a flux material having a firing temperature the same as or lower than a firing temperature of the high magnetization spinel structure;
placing the high magnetization spinel structure within an aperture in the barium tungstate outer structure; and
co-firing the barium tungstate outer structure and the high magnetization spinel structure to shrink the barium tungstate outer structure around the high magnetization spinel structure without the use of adhesive or glue and form a composite material.
13. The method of claim 12 wherein the flux material comprises BiVO 4 .
14. The method of claim 13 wherein the flux material comprises 1-2 wt. % BiVO 4 .
15. The method of claim 12 wherein the flux material comprises 1-10 wt. % MgAl 2 O 4 or CoAl 2 O 4 .
16. The method of claim 12 wherein the barium tungstate is doped with BiVO 4 and one of MgAl 2 O 4 or CoAl 2 O 4 .
17. The method of claim 12 wherein the composite material has a fired density of greater than 5.10 g/cm 3 .
18. The method of claim 12 wherein the composite material is defined by the formula Ba 1-x Bi x W 1-x V x O 4 .
19. The method of claim 12 further comprising forming an isolator or circulator using the composite material.
20. A radiofrequency isolator or circulator comprising:
a high magnetization spinel structure; and
a barium tungstate outer structure surrounding the high magnetization spinel structure, the barium tungstate outer structure doped with a flux material having a firing the same as or lower than a firing temperature of the high magnetization spinel structure.