The low-temperature structural phase transition in CuSO4·5D2O as a function of pressure

Copper sulfate pentahydrate is a common material with a long history of use in testing crystallographic theories and methods. Much of the interest in its behaviour as a model 1-dimensional magnetic system at low T is predicated upon there being no structural phase transition on cooling from room-temperature to 1 Kelvin. However, we now know there to be a structural transition at 32 K in which the unit cell doubles along the a- and c-axis directions due to a change in the site symmetry of one of the independent Cu2+ ions. Coupled with calculations showing that these sites compress in a dramatically different ways, it becomes interesting to investigate the structural phase transition at high pressure. Suitable pressure cells, allowing the requisite high-resolution neutron powder diffraction data have been manufactured and tested on HRPD allowing us to probe the transition to 5.4 kbar.