Structure and Microwave Dielectric Properties of Ca1−xYxTi1−xAlxO3 (CYTA) Ceramics

Abstract

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 ∼200 μm at x = 0 to ∼10 μm 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, ϵr, decreases continuously from 170 to 12, while the microwave quality factor, Q·fr, increases from 10,000 to 12,000 GHz, for x = 0 and 1, respectively. CYTA (x = 0.30) ceramics exhibit ϵr ∼ 38, Q·fr of ∼14,212 GHz, and a temperature coefficient of resonance frequency, τf, of −14 ppm/°C. Small additions of acceptor (0.3 wt% ZnO) or donor (1 wt% Nb2O5) dopants decrease Q·fr by ∼20–30%, respectively.