Deep Dive into Lattice Dynamics and Phonon Anharmonicity for Intrinsically Low Thermal Expansion Coefficient in CuS

Abstract Scientists enquire about materials engineered with high nanoparticle densities with reduced thermal conductivity and excellent thermoelectric performance. An emerging mineral, copper sulfide (CuS) promises a novel paradigm in the proximity of pressure‐driven structural phase transitions to tune its functional and mechanical properties. Though CuS is a thermoelectric material with low lattice thermal conductivity ( ), improvement of its remains a challenge to be addressed. Moreover, the underlying mechanism governing pressure‐induced phase transformation and reasons for intrinsically small remains completely unexplored. In this study, by combining in‐situ vibrational spectroscopy and ab initio calculations, we reveal that strong phonon anharmonicity under high pressure and low temperature demonstrates a promising approach to decreasing efficiently and boosts thermoelectric figure of merit by 2.7 times from its ambient value. A large mode Grüneisen parameter and short lifetimes for acoustic phonons contribute significantly to its thermal transport.