THE EFFECT OF LA2TI3O9 2ND-PHASE ON THE MICROSTRUCTURE AND DIELECTRIC-PROPERTIES OF LA2TI2O7 CERAMICS

Lanthanum dititanate ceramics have been prepared by the mixed oxide ro ute. Up to 6 mol% Nb2O5 or 10 mol% excess TiO2 was added to the starti ng mixes. Sintered products exhibited densities of greater than or equ al to 95% theoretical La2Ti3O9 was present as a second phase in all el oped samples. With the addition of increasing amounts of Nb2O5 or TiO2 there was formation of La2Ti3O9 within the La2Ti3O9 matrix, and the a verage grain size decreased slightly. Dielectric properties were sensi tive to the presence of the second phase. relative permittivity increa sed from 47 to similar to 56 with additions, the dielectric loss tange nt was independent of the amount of excess titania but increased drama tically, when > 3 mol% Nb2O5 was added the temperature coefficient of capacitance (TCC) decreased monotonically from +50 ppm/degrees C for u ndoped La2Ti2O7 ceramics to -50 ppm/degrees C for specimens containing similar to 10 mol% additions. Material with zero TCC can be achieved with the addition of similar to 5 mol%, Nb2O5 or excess TiO2.