Microwave dielectric properties of Sr_0.7Ce_0.2TiO₃–Sr(Mg_1/3Nb_2/3)O₃ ceramics

Abstract

xSr_0.7Ce_0.2TiO₃–(1 − x)Sr(Mg_1/3Nb_2/3)O₃ ceramics, referred to xSCT–(1 − x)SMN, were successfully produced by conventional solid-state sintered technology. The compounds, belonging to perovskites with a secondary phase of CeO₂, can be detected even with x down to 0.1 of SCT composition. The overall trend for grain growth illustrates the increase with increasing SCT doping level. The Raman peak at 825 cm⁻¹ splits into two peaks and causes red shift phenomenon. XPS spectra indicate that Ti and Nb ions exist respectively in tetravalence and pentavalence, and Ce ions exist in trivalence and tetravalence. Dielectrics constant (ε _r ) of SCT–SMN ceramics gradually increases with increasing theoretical dielectric polarizabilities. A wider width of the 825 cm⁻¹ for FWHM of A_1g mode Raman peaks suggests to a lower Q × f value. The increasing tolerance factor in agreement with temperature coefficient of resonant frequency (τ _f ), denotes that the rise of perovskite symmetry. The 0.1SCT–0.9SMN ceramic sintered at 1450 °C for 4 h illustrates excellent microwave dielectric properties with ε _r  ~ 35.4, Q × f ~ 11282 GHz and τ _f  ~ 1.7 ppm/°C. Activation energies of 0.1SCT–0.9SMN ceramic at 100, 300 and 500 V, are ~0.436, 0.427 and 0.331 eV, respectively, indicative of a decreased trend with external electric field.