Structure and Microwave Dielectric Properties of Sr_2+nCe₂Ti_5+nO_15+3n(n≤ 10) Homologous Series

Nominally Sr 2+ n Ce 2 Ti 5+ n O 16+3 n dielectric ceramics were prepared by conventional solid-state ceramic route. The structure and microstructural features of the ceramics were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. At optimized sintering conditions, it is shown that Ce 4+ ions reduce to Ce 3+ ions, which leads to the correct formula Sr 2+ n Ce 2 Ti 5+ n O 15+3 n for the materials. The ceramics present a cubic SrTiO 3 -like structure, where Ce 3+ ions and their associated vacancies randomly share the A - sites with the Sr 2+ cations. Therefore, this solid solution could be alternatively described by Sr 1 - 3 x / 2 Ce x TiO 3, where x ≤ 0.40 is not necessarily an integer. For 0 ≤ n ≤ 10 (0.40 > x > 0.133), these materials have dielectric constant and Q u xf in the range of 113−185 and 6000−11000 GHz (at 2 GHz), respectively. However, the relatively high positive temperature coefficients of resonance frequencies decrease substantially to values five times lower than those commonly observed for SrTiO 3 .