First-principles study of thermal transport properties in ferroelectric HfO₂ and related fluorite-structure...

The discovery of ferroelectricity in the fluorite-structure HfO₂ has attracted much interest in various applications including electro-optic devices and nonvolatile memories. Doping and alloying not only induce ferroelectricity in HfO₂, but also significantly impact the thermal conduction which plays an essential role in the heat dissipation and thermal stability of ferroelectric devices. To understand and regulate the heat transfer in ferroelectric HfO₂, it is crucial to investigate the thermal conduction properties of related fluorite-structure ferroelectrics so as to establish the structure-property relationship. In this work, using first-principles calculations, we investigate the thermal transport in twelve fluorite-structure ferroelectrics. We find an overall satisfactory agreement between the calculated thermal conductivities and those predicted by the simple theory of Slack. Among the family of fluorite-structure ferroelectrics, the transition-metal oxides HfO₂ and ZrO₂ have the highest thermal conductivities due to the strong interatomic bonding. We demonstrate that the spontaneous polarization, a feature specific to ferroelectrics, is positively correlated with the thermal conductivity, namely, the larger the spontaneous polarization, the larger the thermal conductivity. This is of chemical origin, namely, both the spontaneous polarization and the thermal conductivity are positively correlated to the "ionicity" of the ferroelectrics. We further find that the thermal conductivity is several times lower in the ferroelectric solid solution Hf_1-ZrO₂ than in its pure counterparts, especially in the thin films where the finite size effect further suppresses thermal conduction. Our findings suggest the spontaneous polarization as a specific criterion for identifying ferroelectrics with desired thermal conductivities, which may promote the design and application of ferroelectrics.