Résumé
High temperature X ray diffraction performed on recently discovered orthorhombic Th2O(PO4)(2) shows a continuous linear thermal contraction (-1.6 x 10(-6)degrees C-1) in 20-600 degrees C range and a near-zero expansion at higher temperatures resulting from a dual structural deformation involving oxygen oscillations and inter-cations repulsions. Although similar mechanisms were observed in isotypic Zr2O(PO4)(2) (+1.5 x 10(-6)degrees C-1) and U2O(PO4)(2) (-1.4 x 10(-6)degrees C-1), those observed in Th2O(PO4)(2) are particularly intense because of the high ionic radius of tetravalent thorium. (C) 2011 Elsevier Ltd. All rights reserved.