Phonon anharmonicity and negative thermal expansion in SnSe

Abstract

The anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy, in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. The origin of the anharmonic phonon thermodynamics is linked to the electronic structure.

14 pages, 12 figures

References in corpus (4)

• Giant Anharmonic Phonon Scattering in PbTe
• Low thermal conductivity and triaxial phononic anisotropy of SnSe
• Electronic structure and thermoelectric properties of n- and p-type SnSe from first principles calculations
• Structural Changes in Thermoelectric SnSe at High Pressures

Cited by in corpus (7)

• Anharmonic phonon spectra of PbTe and SnTe in the self-consistent harmonic approximation
• Thermal Expansion in Insulating Solids From First Principles
• Evidence for hard and soft substructures in thermoelectric SnSe
• Thermally-Enhanced Fröhlich Coupling in SnSe
• Light-Induced Nonthermal Phase Transition to the Topological Crystalline Insulator State in SnSe
• Four-Dimensional Imaging of Lattice Dynamics using Inelastic Scattering
• Phonons and Anomalous Thermal Expansion Behaviour in Crystalline Solids