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–(Ti_0.5Nb_0.5)O₆–TiO₆–(Ti_0.5Nb_0.5)O₆–Cs in the tripled octahedra. On the other hand, in CsCaLaTiNb₂O₁₀, there is a rather complicated fashioning of Cs–(Ti_0.15Nb_0.85)O₆–(Ti_0.70Nb_0.30)O₆–(Ti_0.15Nb_0.85)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, H_0.95Cs_0.05La₂Ti₂NbO₁₀·1.3H₂O, can be easily reacted with n-alkylamines.