Correlation between spontaneous polarization and thermal conductivity in ferroelectric HfO2 from first principles

Abstract

The ferroelectric phase of hafnia (ferroelectric HfO2) has been considered as a promising ferroelectric material for nanoscale electronic devices due to its robust ferroelectricity that is characterized by an electric-field-switchable spontaneous polarization. A perhaps long overlooked and hence rarely explored property in ferroelectric HfO2 is the thermal conduction, which plays an important role in the thermal management and thermal stability of related ferroelectric devices. Both the spontaneous polarization and thermal conduction are intimately related to the lattice anharmonicity. It is hence natural to expect a correlation between the two quantities. In this work, we use efficient tailoring strategies such as pressure and strain engineering to investigate such a correlation. The calculated thermal conductivity of ferroelectric HfO2 is 14.1 W m−1 K−1 at room temperature. We find that indeed the spontaneous polarization and thermal conductivity are positively correlated under pressure or strain in ferroelectric HfO2, namely the larger the spontaneous polarization, the larger the thermal conductivity, regardless of whether the spontaneous polarization or thermal conductivity is enhanced or suppressed. This is attributed to the dominant role of lattice anharmonicity, i.e., under a hydrostatic pressure or a compressive strain, the lattice becomes increasingly harmonic with an enhanced spontaneous polarization, facilitating the thermal transport. We further demonstrate such a correlation in three other representative ferroelectrics (i.e., tetragonal PbTiO3, wurtzite AlN, and hexagonal ABC ferroelectric LiBeSb), indicating that this may be a universal feature. The positive correlation between spontaneous polarization and thermal conductivity is further corroborated by their concurrent reductions with rising temperature. This work paves the way to establish the structure-property relation in ferroelectric HfO2 and may offer novel avenues for the designs and applications of ferroelectric materials.