Structure and microwave dielectric properties of Ca1− xY xTi1− xAl xO3 (CYTA) ceramics

The structure and dielectric properties of Ca1-xYxTi1-xAlxO3 (CYTA) ceramics prepared by the mixed-oxide route have been investigated. CYTA forms a complete solid solution with an orthorhombic perovskite structure. Residual. Y4Al2O9 and Y3Al5O12 resulting from incomplete reaction are observed for >= 0.9. Scanning electron microscopy shows that CYTA ceramics exhibit uniform microstructures, with an average grain size that decreases from similar to 200 mu m at x 0 to similar to 10 mu m at x = 1.0. Transmission electron microscopy of CYTA (x = 0.3) ceramics reveals the presence of ferroelastic domains, and electron-diffraction patterns are indexed on the Pnma space group, consistent with an a(+)b(-)b(-) octahedral tilted structure. The relative permittivity, Er, decreases continuously from 170 to 12, while the microwave quality factor, Q(.)f(r), increases from 10,000 to 12,000 GHz, for x = 0 and 1, respectively. CYTA (x ceramics exhibit epsilon(r) similar to 38, Q(.)f(r) of similar to 14,212 GHz, and a temperature coefficient of resonance frequency, tau(f) of -14 ppm/degrees C. Small additions of acceptor (0.3 wt% ZnO) or donor (I wt% Nb2O5) dopants decrease Q(.)f(r) by similar to 20-30%, respectively. 0.30).