Giant Negative Linear Compressibility in Orthorhombic Copper Cyanide

Most reported negative linear compressibility (NLC) materials exhibit either a small NLC over a large pressure range or a high NLC over a very small pressure range. Here, we report the remarkable discovery of giant NLC in the low-temperature form of CuCN (LT-CuCN) over an unusually large pressure range. High-pressure XRD studies on LT-CuCN observed the NLC of -20.5 TPa-1 along the a-axis at zero pressure, and the ambient orthorhombic phase remained stable up to 9.8 GPa. Pressure and temperature-dependent Raman studies identified the phonon vibrations responsible for NLC and negative thermal expansion (NTE).