Effects of B-site substitution and annealing on the structural and microwave dielectric properties of CaTiO3 ceramics

Abstract

CaTi1−x (Al0.5Ta0.5) x O3 (0.2 ≤ x ≤ 0.55) ceramics were synthesized by a conventional solid-state reaction method, and the effects of B-site substitution and annealing temperature on the structural and microwave dielectric properties of CaTi1−x (Al0.5Ta0.5) x O3 ceramics were investigated. The XRD patterns reveal the formation of single solid solution phase with orthorhombic structure for all studied compositions (0.2 ≤ x ≤ 0.55) and the unit cell volume decreases linearly with an increment of x. The SEM results suggest no evidence of secondary phase. The permittivity (er) and temperature coefficient of resonant frequency (τ f ) decrease obviously with an increase of x. And the substitution of (Al0.5Ta0.5)4+ for Ti4+ improves the quality factor (Q × f). The permittivity of sintered samples decreases from 85.47 to 38.38 and the temperature coefficient of resonate frequency values (τ f ) varies from 211.78 to −38.37 ppm/°C with x increasing from 0.2 to 0.55. Moreover, the Q × f values of the sintered samples are obviously affected by the annealing temperature. Optimized microwave dielectric properties with er ~ 47.94, Q × f ~ 21602.45 GHz, τ f ~ 5.25 ppm/°C are achieved at x = 0.45 when sintered at 1580 °C and annealed at 1450 °C for 15 h, suitable for use in satellite broadcast systems due to high frequency selectivity.