Crystal structure and phonon modes of disorder induced Ba2Li1-xTe1+xO5.5+δ (x =0, 0.1, 0.2) double perovskite based microwave dielectrics

Abstract

An extensive investigation that correlates structural and microwave dielectric properties of oxygen deficient double perovskites, Ba2Li1-xTe1+xO5.5+δ (x = 0, 0.1, 0.2) is reported for the first time. Even though XRD data supports a pseudocubic structure for Ba2Li1-xTe1+xO5.5+δ ceramics, a detailed investigation using Raman and FTIR spectra followed by Rietveld refinement indicates the most likely space group is P21/n for all compositions. Further, temperature dependent Raman spectra illustrate the thermal stability of the compositions between −180°C to 400°C. XPS studies of sintered ceramics confirm more than 95% of Te in 6+ oxidation state. The compounds exhibit maximum densification at 950°C with the addition of 1 wt% B2O3. Ba2Li0.8Te1.2O6 ceramics have temperature stable microwave dielectric properties of εr = 16.9, Q×f = 15410 GHz and τf = −3.7 ppm/°C and it does not react with Ag electrodes at 940°C, which makes it a suitable candidate for low temperature co-fired ceramics applications.