Design of Microwave Ceramics

Unfortunately, two fundamental relationships work against the existence of an ideal dielectric microwave ceramics  

strategies are required to balance e, Tj, and Q by grain boundary engineering. Several routes towards materials with improved characteristic dielectric parameters are outlined in Section 8.4.1 (see also Wersing, 1996). 

Since oxygen vacancy defects also tend to decrease the Q-factor, the firing atmosphere and post-firing anneahng must be carefully considered. This is reminiscent of the severe processing problems of high-temperature superconductors (see Section 9.7). In fact, the dielectric loss in ceramics is analogous to the resistance experienced by flux penetration in type 11 superconductors. 

Grain boundary engineering by doping BaTi409 with as little as 2 mol% tungsten oxide (WO3) yields ceramics with temperature coefficients of the resonance 

The introduction of neodymium into barium titanate leads to a product with a high dielectric permittivity of 80, which is attributed to a single-phase BaNd2TisOi4 (NBT), analogous to the phase described above in samarium-doped barium 

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