Time resolved studies of the effect of cyanide order on phonon softening in the cubic NTE material Cd(CN)2

Materials which exhibit negative thermal expansion (NTE) are used in a number of applications to counteract the usual positive thermal expansion (PTE) of ordinary materials. Cubic cadmium cyanide is amongst the most important isotropic NTE materials with behaviour more than twice as extreme as that of better known systems such as ZrW2O8. Despite its importance, little is understood about lattice dynamics of Cd(CN)2; this is partly because the orientations of the molecular CN anion exhibit correlated disorder of a kind which has only recently been characterised. Our hypothesis is that CN orientational disorder affects the lattice dynamics responsible for NTE in Cd(CN)2. By studying the time-evolution of the inelastic neutron scattering after an abrupt cooling step, we will be able to extract the effect of long-timescale CN reorientations on the vibrational modes responsible from NTE.