A new neodymium cyclotriphosphate pentahydrate powder, NdP3O9 center dot 5H(2)O, has been prepared using a classical chemistry method and characterized by X-ray diffraction and infrared spectroscopy techniques. The IR spectrum Shows the characteristic bands of cyclotriphosphates as the triplet in the range 1055-1007-917 cm (1). The thermal behavior of the titled compound was also carried Out using conventional thermal analysis techniques (TG and DSC) under air atmosphere and Controlled transformation Rate Thermal Analysis (CRTA) technique under constant water vapour pressure of 5 hPa. It was shown that thermal treatment in air, with linear heating rate of 10 K min(-1), favourites the structure breakdown as soon as the release of water molecules starts. In this case art amorphous compound is obtained, which then crystallizes at 1073 K and gives the polyphosphate Nd(PO3)(3). However, by CRTA technique at P-H2O = 5 hPa, the water molecules at e eliminated with a lower rate which permits to save the initial Structure up to an advanced dehydration step. The breakdown of the initial structure is immediately followed by the crystallization of the anhydrous polyphosphate Nd(PO3)(3) phase in the temperature range 455 K < T < 793 K. (C) 2009 Elsevier B.V. All rights reserved.