Crystal structure, Raman spectroscopy and microwave dielectric properties of layered-perovskite BaA₂Ti₃O₁₀ (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 (ε_r) increased due to decrease in molar volume of the compound, which was observed as a result of smaller ionic radii. Quality factor (Q × ƒ) 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 A_g mode. The temperature coefficient of resonant frequency (τ_ƒ) was correlated with respective octahedral-distortion in the structure. - Highlights: • Increase of B-site bond strength enhanced the quality factor. • FWHM of A_g mode also confirmed the increase of quality factor from Sm to La. • Effect of B-site octahedral distortion on τ_f