B-site cation arrangement and crystal structure of layered perovskite compounds CsLn2Ti2NbO10 (Ln = La, Pr, Nd, Sm) and CsCaLaTiNb2O10

Abstract

B-site cation arrangement and crystal structure in the layered perovskite compounds CsLa2Ti2NbO10 (Ln = La, Pr, Nd, Sm) and CsCaLaTiNb2O10 have been investigated by the Rietveld analysis of the powder X-ray diffraction patterns, lattice energy calculations, and intercalation reactions. In CsLa2Ti2NbO10, equal numbers of Ti4+ and Nb5+ cations were statistically distributed in the outer octahedra, and only Ti4+ cations occupied the middle octahedra. These oxides represent the first example of layered perovskites, in that the B-site cations are distributed in the ordering sequence of Cs–(Ti0.5Nb0.5)O6–TiO6–(Ti0.5Nb0.5)O6–Cs in the tripled octahedra. On the other hand, in CsCaLaTiNb2O10, there is a rather complicated fashioning of Cs–(Ti0.15Nb0.85)O6–(Ti0.70Nb0.30)O6–(Ti0.15Nb0.85)O6–Cs, not the ordering sequence of Cs–NbO6–TiO6–NbO6–Cs. It can be demonstrated that the B-site cation arrangement is partly determined by the electrostatic stabilization of the CsO rock salt interlayer, which can be confirmed from the lattice energy calculation. Since half of the NbO6 in CsLa2Ti2NbO10 is positioned with half of the TiO6 in the outer octahedra, its protonated phase, H0.95Cs0.05La2Ti2NbO10·1.3H2O, can be easily reacted with n-alkylamines.