Crystal structure, Raman spectroscopy and microwave dielectric properties of layered-perovskite BaA<inf>2</inf>Ti<inf>3</inf>O<inf>10</inf> (A = La, Nd and Sm) compounds

Dependence of microwave dielectric properties on the structural characteristics of BaA2Ti3O10 (A = La, Nd and Sm) was investigated. All the compounds were prepared by solid-state reaction method and the structural parameters were obtained from Rietveld refinement of powder diffraction data of the compounds. The dielectric constant (εr) increased due to decrease in molar volume of the compound, which was observed as a result of smaller ionic radii. Quality factor (Q) of BaSm2Ti3O10 (BST) and BaLa2Ti3O10 (BLT) were found to be lowest (10,490 GHz) and highest (20,860 GHz) respectively, which was explained in terms of average bond strength between B-site cations and oxygen anions. Raman spectroscopy was also used to analyze the B-O bond strength with the help of Ag mode. The temperature coefficient of resonant frequency (τO) was correlated with respective octahedral-distortion in the structure.