Synthesis strategy, phase-chemical structure and microwave dielectric properties of paraelectric Sr(1−3x/2)CexTiO3 ceramics

Phase formation, chemical structure and microwave (MW) dielectric behavior of A-site Ce-doped SrTiO3 ceramics sintered in close aluminum pipe have been investigated. Samples with x = 0.4 appeared cubic by X-ray diffraction (XRD) but exhibited splitting and superstructure reflections in the range of 0.45 ≤ x ≤ 0.6. X-ray photoelectron spectroscopy (XPS) analysis revealed the sample possesses mixed-valent states of Ti3+/Ti4+ upon oxygen vacancy formation. As the x value increases, the Q × f value increases slightly from 7569 to 22,682 GHz, but the temperature coefficient of resonant frequency (τf) decreases markedly from +372 to +5 ppm/°C. A novel combination of microwave dielectric properties: εr = 61, Q × f = 22,682 GHz and τf = +5 pmm/°C were achieved for composition Sr0.1Ce0.6TiO3 at 1300 °C for 3 h.