X-ray structural study on the different redox behavior of La and Pr oxysulfates/oxysulfides

X-ray Rietveld analysis was performed to study the structural aspects of the different reduction/reoxidation behavior between Ln(2)O(2)SO(4) and Ln(2)O(2)S (Ln = La and Pr). The two oxysulfates, Ln(2)O(2)SO(4), and their reduced forms, Ln(2)O(2)S, are composed of alternative stacking of Ln(2)O(2)(2+) and SO42- or S2-. Not only interatomic distances but also bond angles of La2O2S and Pr2O2S were very similar. By contrast, a noticeable difference was observed for the oxysulfate, i.e., the S-O distances and the O-S-O angles, suggesting that larger distortion in the SO4 unit is a possible reason for the faster reduction of Pr2O2SO4 compared to La2O2SO4. (C) 2007 Elsevier B.V. All rights reserved.