Giant Negative Linear Compressibility in Orthorhombic Copper Cyanide

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Negative linear compressibility (NLC) is a rare phenomenon where a material contracts along one dimension under hydrostatic pressure.
• Existing NLC materials typically show limited NLC magnitude or operate over narrow pressure ranges.

Purpose of the Study:

• To report the discovery of giant NLC in a novel material.
• To investigate the pressure and temperature dependence of NLC and its underlying mechanisms.

Main Methods:

• High-pressure X-ray diffraction (XRD) studies to measure structural changes under pressure.
• Variable temperature and pressure Raman spectroscopy to probe phonon dynamics.

Main Results:

• Observed giant NLC of -20.5 TPa⁻¹ along the a-axis in LT-CuCN at ambient conditions.
• The orthorhombic phase of CuCN remained stable up to 9.8 GPa.
• Identified specific phonon vibrations linked to both NLC and negative thermal expansion (NTE).

Conclusions:

• LT-CuCN exhibits unprecedented giant NLC over an extended pressure range.
• Phonon modes are confirmed as the origin of both NLC and NTE in this material.
• This discovery opens avenues for designing materials with tunable compressibility.