Much effort has been devoted to the research of new NTE materials and the understanding of the mechanism driving this phenomenon. As part of our ERC grant on ‘orbital molecules’, we have recently discovered that the vanadium oxyphosphate V2OPO4 displays NTE at high temperatures associated with a charge ordering transition. To determine the origin of the NTE, we propose to measure precise atomic coordinates and anisotropic thermal displacement parameters as a function of temperature from RT to 1200 K, well above TCO = 605 K, through neutron powder diffraction. Neutrons are needed to obtain accurate information for the oxygen atoms. 2 days are required to collect a series of patterns in the RT-1200 K range, during heating and cooling, using a 3g powder sample.