Crystal structure and optical properties of B site-ordered ALaLiTeO 6 (A = Ba, Sr) ceramics

Abstract B site ordered double perovskites ALaLiTeO 6 (A = Ba, Sr) were synthesized through solid state route and vibrational phonon modes were investigated for the first time using Raman spectroscopy to find the exact crystal symmetry. Even though X-ray diffraction indicated a cubic symmetry, a detailed Raman analysis showed a lower symmetry possibly due to tilting of octahedra. The obtained first order Raman modes are 8 for BaLaLiTeO 6 and 13 for SrLaLiTeO 6 . Evaluated phonon modes were in good agreement with the corresponding group theoretical predictions for space group I4/m (for BaLaLiTeO 6 ) and P2 1 /n (for SrLaLiTeO 6 ). Rietveld refinement of the XRD patterns further confirm the space groups obtained for BaLaLiTeO 6 and SrLaLiTeO 6 and also show that 1:1 B site ordering of Te 6+ and Li + cations is present in both the compounds. Optical band gap of these compounds were found to be 3.5 eV for BaLaLiTeO 6 and 4.0 eV for SrLaLiTeO 6 .