Structure and Microwave Dielectric Behavior of A‐Site‐Doped Sr _{(1−1.5 <i>x</i> )} Ce _<i>x</i> TiO ₃ Ceramics System

Abstract

The ion valence state, phase composition, microstructure, and microwave dielectric properties of Sr (1−1.5 x ) Ce x TiO 3 ( x = 0.1–0.67, SCT) ceramics were systematically investigated. Sr (1−1.5 x ) Ce x TiO 3 ceramics were produced with gradual structural evolution from a cubic to a tetragonal and turned to an orthorhombic structure in the range of 0.1 ≤ x ≤ 0.67. Above a critical Ce proportion ( x = 0.4), microstructural changes and normal grain growth initially occurred. On the basis of chemical analysis results, the reduction of Ti 4+ ions was hastened by tetravalent ions (Ce 4+ ). By contrast, this reduction was inhibited by trivalent ions (Ce 3+ ). The observed dielectric behavior was strongly influenced by phase composition, oxygen vacancies ( ), and defect dipoles, namely, ( ) and ( ). Temperature stable ceramics sintered at 1350°C for 3 h in air yielded an intermediate value of dielectric constant (ε r = 40), with the smallest reported value of temperature coefficient of resonant frequency (τ f = +0.9 ppm/°C), and quality factor ( Q × f = 5699 GHz) at x = 0.6.