MICROWAVE DIELECTRIC-PROPERTIES OF LANTHANIDE TITANATE CERAMICS

Microwave dielectric property changes with substitution of La3+ by Nd3+ and/or Sm3+ ions are studied for La2 Ti2O7 and La4Ti9O24 ceramics. For the monoclinic La2Ti2O7, the substitution causes a considerable decrease in the permittivity (epsilon(r)) of the material from epsilon(r) = 17 (La) to epsilon(r) = 36 (Nd), with a simultaneous variation in the Q.f value from 8500 to 16000 GHz. In La4Ti9O24-type dielectrics, only a slight change is observed in both the epsilon(r) (almost-equal-to 37) and Q.f values (almost-equal-to 24000 GHz) by lanthanide substitution. The effects of mixing of different dielectric materials on the microwave properties are also examined for La2Ti2O7-La4Ti9O24 and Nd2Ti2O7-Nd4Ti9O24 composites. The permittivity and temperature coefficient of resonant frequency of the composite ceramics can be controlled using Lichteneker's rule, whereas the mixing of the different dielectrics results in the substantial lowering of the Q.f value.