High temperature X ray diffraction performed on recently discovered orthorhombic Th 2 O(PO 4 ) 2 shows a continuous linear thermal contraction (−1.6×10 −6 °C −1 ) in 20–600°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 Zr 2 O(PO 4 ) 2 (+1.5×10 −6 °C −1 ) and U 2 O(PO 4 ) 2 (−1.4×10 −6 °C −1 ), those observed in Th 2 O(PO 4 ) 2 are particularly intense because of the high ionic radius of tetravalent thorium.