Pressure dependance of soft mode phonons in cubic NTE material Cd(CN)2

Cubic cadmium cyanide is one of the most important negative thermal expansion (NTE) materials, meaning that it shrinks rather than expands when heated. Understanding the vibrations in the vibrations present in Cd(CN)2 and how they change as the material is compressed is central to understanding this materials NTE. Counterintuitively, as our material is compressed it becomes easier to compress, which indicates that more study into the vibrations under pressure may reveal something about the underlying causes of NTE. This approach has been taken successfully for the better known NTE material, ZrW2O8, but not yet with Cd(CN)2, which exhibits a behaviour more than twice as extreme.