Raman spectra of the solid-solution between Rb2La2Ti3O10 and RbCa2Nb3O10

A site preference of niobium atom in Rb2-xLa2Ti3-xNbxO10 (0.0≤x≤1.0) and RbLa2-xCaxTi2-xNb1+xO10 (0.0≤x≤ 2.0), which are the solid-solutions between Rb2La2Ti3O10 are RbCa2Nb3O10, has been investigated by Raman spectroscopy. The Raman spectra of Rb2-xLa2Ti3-xNbxO10 (0.0≤x≤1.0) gave an evidence that niobium atoms substituted for titanium atoms preferably occupy the highly distorted outer octahedral sites rather than the central ones in triple-octahedral perovskite layers. In contrast, the Raman spectra of RbLa2-xCaxTi2-xNb1+xO10 (0.0≤x≤ 2.0) showed no clear information for the cationic arrangement in perovskite slabs. This difference indicated that a site preference of niobium atoms is observed only when the linear Rb-O-Ti linkage can be replaced by much stronger terminal Nb-O bond with double bond character. From comparison with the Raman spectroscopic behavior of CsLa2-xA'xTi2-xNb1+xO10 (A' = Ca and Ba; 0.0 ≤x≤), it is also proposed that a local difference in arrangement interlayer atoms causes a significantly different solid acidity and photocatalytic activity of the layered perovskite oxides, despite their crystallographically similar structures