Structure and Microwave Dielectric Properties of Ca_1−xY_xTi_1−xAl_xO_3 (CYTA) Ceramics

The structure and dielectric properties of Ca 1− x Y x Ti 1− x Al x O 3 (CYTA) ceramics prepared by the mixed-oxide route have been investigated. CYTA forms a complete solid solution with an orthorhombic perovskite structure. Residual Y 4 Al 2 O 9 and Y 3 Al 5 O 12 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, ϵ r , 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 = 0.30) ceramics exhibit ϵ r ∼ 38, Q·f r of ∼14,212 GHz, and a temperature coefficient of resonance frequency, τ f , of −14 ppm/°C. Small additions of acceptor (0.3 wt% ZnO) or donor (1 wt% Nb 2 O 5 ) dopants decrease Q·f r by ∼20–30%, respectively.