Anomalous behavior of strain modulated lattice thermal transport in piezoelectric crystals and the effect of polarization

Abstract

Strain is known to influence the lattice dynamics of crystalline solids. Its effect is generally expressed in a decrease of the lattice thermal conductivity as the stress is varied from compression to tension. However, the results of our ab initio calculations suggest that under a uniaxial strain along the c-axis, the lattice thermal conductivity of PbTiO3, a typical piezoelectric material, actually increases from compression to tension going through a maximum at the unstrained state. We find that both tensile and compressive strains reduce considerably the phonon mean free path. Strain also modifies remarkably the phonon group velocity and lifetime of the low-frequency acoustic modes. This unusual strain dependence largely comes from a competing effect of the electrical polarization and the elastic stiffness on the phonon velocity due to their opposite strain dependence. Based on these results, we predict an unexpected thermal transport behavior due to the piezoelectric effect and reveal the significant role of the electrical polarization in lattice thermal transport. This work may thus inspire the development of polarization engineering as a new avenue towards manipulation of heat conduction bringing to the light the previously unrecognized potential of piezoelectric materials for thermal modulation applications.