Microwave Dielectric Properties of Hexagonal 12R‐Ba 3 LaNb 3 O 12 Ceramics

The dielectric properties of dense ceramics of the n =0 member of a newly identified homologous series Ba 3+ n LaNb 3 Ti n O 12+3 n , where n =0, 1, and 2, are reported. Single‐phase powders can be obtained from the mixed‐oxide route at 1350°C and dense ceramics (>97% of the theoretical X‐ray density) with uniform microstructures (3–5 μm) can be obtained by sintering in air at 1500°C. The ceramics are excellent dc insulators with a band gap >2.6 eV that resonate at microwave frequencies with a relative permittivity, ɛ r ∼44, a quality factor, Q × f r , of ∼9000 at f r ∼5.5 GHz and a temperature coefficient of resonant frequency, TC f ,∼−100 ppm/K.