Vibrational Study of Layered Perovskites M₂La₂Ti₃O₁₀ (M = Li, Na, K, Rb):  Raman Spectra and Normal Mode Analysis

Abstract

Vibrational study by Raman spectroscopy was made of the layered perovskite compounds of the formula M 2 La 2 Ti 3 O 10 (M = H, Li, Na, K, Rb), K 2 La 2 Ti 3 O 10 ·2H 2 O, and H 2 La 2 Ti 3 O 10 · n H 2 O. The spectral features above 400 cm -1 were similar in all of the unhydrated samples suggesting that the bands originated from the vibrational modes of the La 2 Ti 3 O 10 perovskite layer. Lattice dynamical calculations were performed with the use of a potential field derived from the molecular dynamics on the M 2 La 2 Ti 3 O 10 (M = Li, Na, K). The assignment of the Raman bands higher than 400 cm -1 was made on the basis of the results of lattice dynamical calculations and was confirmed by comparing the spectral feature of K 2 La 2 Ti 3 O 10 with that of H 2 La 2 Ti 3 O 10, K 2 La 2 Ti 3 O 10 ·2H 2 O, and H 2 La 2 Ti 3 O 10 · n H 2 O.