We use a combination of variable-temperature / variable-pressure neutron powder diffraction, variable-pressure inelastic neutron scattering, and quantum chemical calculations to interrogate the behaviour of the negative thermal expansion (NTE) material 114Cd(CN)2 under hydrostatic pressure. We determine the equation of state of the ambient-pressure phase, and discover the so-called `warm hardening' effect whereby the material becomes elastically stiffer as it is heated. We also identify a number of high-pressure phases, and map out the phase behaviour of Cd(CN)2 over the range 0≤p≤0.5\,GPa, 100≤T≤300\,K. As expected for an NTE material, the low-energy phonon frequencies are found to soften under pressure, and we determine an effective Gr{\"u}neisen parameter for these modes. Finally, we show that the elastic behaviour of Cd(CN)2 is sensitive to the local Cd coordination environment, which suggests an interplay between short- (phononic) and long-timescale (cyanide flips) fluctuations in Cd(CN)2.
@article{arxiv.2302.09963,
title = {Structure and dynamics of the negative thermal expansion material Cd(CN)$_2$ under pressure},
author = {Chloe S. Coates and Mia Baise and Johanthan M. Bulled and Emma H. Wolpert and Joshua W. Makepeace and Helen C. Walker and Alexandra S. Gibbs and A. Dominic Fortes and Ben Slater and Andrew L. Goodwin},
journal= {arXiv preprint arXiv:2302.09963},
year = {2023}
}