Synthesis of 0.65CaTiO₃–0.35SmAlO₃ ceramics and effects of La₂O₃/SrO doping on their microwave dielectric properties

Abstract

0.65CaTiO₃–0.35SmAlO₃ ceramics were synthesized via four calcination methods using a conventional solid-state technique. The reaction mechanism occurred between mixtures of CaCO₃, TiO₂, Sm₂O₃, and Al₂O₃ was studied by X-ray diffraction patterns. Sm₂TiO₇, CaSmAl₃O₇, Sm₄Ti₉O₂₄ were detected in calcined mixtures, which could be converted into CaTiO₃–SmAlO₃ in ultimate sintered ceramics at a high temperature. Through comparing the comprehensive properties of 0.65CT–0.35SA ceramics sintered at 1450 °C, we determined the best calcination path as the fourth method. We then introduced La₂O₃/SrO to CTSA ceramics synthesized by the fourth method to improve the overall properties. Thereafter, the phase composition, microstructure, densification, dielectric performances and sintering characteristic of 1 wt% SrO doped 0.65CT–0.35SA specimens with various La₂O₃ additions were comprehensively investigated. We observed that after adding La₂O₃/SrO additives, the sintering temperature of CTSA ceramics was depressed to 1340 °C, while facilitating dielectric performances. However, the second-phase La₁₀Al₄O₂₁ occurred due to the excessive amounts of La₂O₃ additions, which degraded the dielectric properties of 0.65CT–0.35SA ceramics. Synthetical properties of ε_r = 42.94, Q × f = 43680 GHz (f = 5.1 GHz), and τ_f = − 3.39 ppm/°C were achieved for 1 wt% SrO doped 0.65CT–0.35SA specimens with 0.5 wt% La₂O₃ additions sintered at 1340 °C, which were likely to be promising option for practical application.