Structure and Microwave Dielectric Behavior of A-Site-Doped Sr(1-1.5x)CexTiO3 Ceramics System

The ion valence state, phase composition, microstructure, and microwave dielectric properties of Sr(1 - 1.5x) CexTiO3 (x = 0.10.67, SCT) ceramics were systematically investigated. Sr(1 - 1.5x) CexTiO3 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 Ti4+ ions was hastened by tetravalent ions (Ce4+). By contrast, this reduction was inhibited by trivalent ions (Ce3+). The observed dielectric behavior was strongly influenced by phase composition, oxygen vacancies (V-O(center dot center dot)), and defect dipoles, namely, (Ti' - V-O(center dot center dot)) and (V-Sr '' - V-O(center dot center dot)). Temperature stable ceramics sintered at 1350 degrees C for 3 h in air yielded an intermediate value of dielectric constant (epsilon(r) = 40), with the smallest reported value of temperature coefficient of resonant frequency (tau(f) = + 0.9 ppm/degrees C), and quality factor (Q x f = 5699 GHz) at x = 0.6.