Vibrational Spectroscopy of Ca₂LnTaO₆(Ln = lanthanides, Y, and In) and Ca₂InNbO₆Double Perovskites

Ca 2 LnTaO 6 (Ln = lanthanides, Y, and In) and Ca 2 InNbO 6 ceramics were prepared by the solid-state route, and their vibrational properties were investigated using Raman scattering and infrared spectroscopy. The correct crystal structure and phonon mode features for this lanthanide series in Ca-based double perovskites were determined using experimental data besides group-theoretical models. It was observed that the ceramics with Y, Er, and In exhibit orthorhombic, Pbnm ( D 2 h 16 ) structures, similarly to those previously observed in Ca 2 LnNbO 6 ceramics, whereas the materials with La, Nd, Sm, Eu, Gd, Tb, and Ho show a monoclinic P 2 1 / n ( C 2 h 5 ) structure, like Sr 2 LnTaO 6 ceramics. Together with another two previous publications (Dias, A.; Khalam, L. A.; Sebastian, M. T.; Paschoal, C. W. A.; Moreira, R. L. Chem. Mater. 2006, 18, 214−220 and Dias, A.; Khalam, L. A.; Sebastian, M. T.; Lage, M. M.; Matinaga, F. M.; Moreira, R. L. Chem. Mater. 2008, 20, 5253−5259), the present results conclude the study for the A 2 LnTaO 6 materials with alkaline-earth metals in the A-site, showing the changing in the crystalline structure as a function of the chemical environment.