High-Q microwave dielectric properties in the Na0.5Sm0.5TiO3 + Cr2O3 ceramics by one synthetic process

The Na0.5Sm0.5TiO3 + x mol Cr2O3 ceramics ( x = 0, 0.25%, 0.5%, 0.75%, 1%, 1.25% and 1.5%) were conventionally prepared using solid-state reaction method by one synthesizing process. All specimens were identified as a structure of orthorhombic perovskite with Pnma space group. Both of XRD patterns and refinement results showed that the Cr3+ had incorporated into the lattice at Ti sites, leading to the expansion of cell volume. The densification can be improved by adding a proper amount of Cr2O3 (0.25% <= x <= 1%). The permittivity (er) slightly increased with x <= 0.25%, later decreased with further addition of Cr2O3, which showed a similar varying trend to dielectric polarizabilities. The temperature coefficient of the resonant frequency (T-f) was reduced from 199.3 ppm/degrees C to 160.8 ppm/degrees C due to an increase of B- site bond valence. The experimental XPS results confirmed that there was a significant increase of quality factor (Q x f) from 8993 GHz at x = 0-11854 GHz at x = 1% due to the restraint of Ti4+ reduction to Ti3+. When added with 1% mol Cr2O3, the Na1/2Sm1/2TiO3 ceramic sintered at 1450 degrees C for 2 h exhibited high microwave dielectric properties of epsilon(r) - 96, Q x f - 11854 GHz and T-f - 171.2 ppm/degrees C. (C) 2017 Elsevier B.V. All rights reserved.