Anomalous thermal transport in MgSe with diamond phase under pressure

Abstract

Most materials exhibit a monotonically increasing lattice thermal conductivity with pressure. However, in this work, we report anomalous thermal transport properties of MgSe with a diamond phase under high pressure by first-principles calculations. Unlike other selenides, the lattice thermal conductivity of MgSe decreases with increasing pressure. We attribute this anomalous thermal transport to both harmonic and anharmonic effects. The harmonic effect is related to the anomalous downward shift of the transverse acoustic modes, which leads to decreasing phonon group velocities. This anomalous harmonic effect can also be confirmed by anomalous soft elastic properties. The anharmonic effect, on the other hand, is related to the stronger anharmonic scattering strength under pressure. Through bonding analysis, we found that the alternating bonding and antibonding states, combined with the unique lattice structure, are the main reason behind this anomaly. Our results reveal that the abnormal soft elastic properties under pressure can be a new way to judge whether lattice thermal conductivity decreases with pressure.