Large Thermal Conductivity Switching in Ferroelectrics by Electric Field-Triggered Crystal Symmetry Engineering

Ultralow Lattice Thermal Transport and Considerable Wave-like Phonon Tunneling in Chalcogenide Perovskite BaZrS3

Chalcogenide perovskites provide a promising avenue for nontoxic, stable thermoelectric materials. Here, the thermal transport and thermoelectric properties of BaZrS3 as a typical orthorhombic perovskite are investigated. An extremely low lattice thermal conductivity κL of 1.84 W/mK at 300 K is revealed for BaZrS3, due to the softening effect of Ba atoms on the lattice and the strong anharmonicity caused by the twisted structure. We demonstrate that coherence contributions to κL, arising from wave-like phonon tunneling, lead to an 18% thermal transport contribution at 300 K. The increasing temperature softens the phonons, thus reducing the group velocity of materials and increasing the scattering phase space. However, it simultaneously reduces the anharmonicity, which is dominant in BaZrS3 and ultimately improves the particle-like thermal transport. In addition, via replacement of the S atom with Se- and Ti-alloying strategy, the ZT value of BaZrS3 is significantly increased from 0.58 to 0.91 at 500 K, making it an important candidate for thermoelectric applications.

Phonon thermal transport in ferroelectricα-In2Se3 via first-principles calculations

Two-dimensional (2D) ferroelectrics are promising candidates in the field of microelectronics due to their unique properties such as excellent photoelectric responsiveness. However, the thermal properties of 2D ferroelectrics are less investigated. Here, the thickness dependent thermal conductivity in ferroelectricα-In2Se3is systematically investigated by the first-principles method combined with the phonon Boltzmann transport equation. On this basis, the strain and oxidation effects on the thermal conductivity of monolayerα-In2Se3is further studied. The calculation results show that the thermal conductivity has a significant reduction with decreasing film thickness or increasing tensile strain, and the anharmonic phonon-phonon scattering rate is the intrinsic mechanism for the reduction in thermal conductivity. On the other hand, the replacement of Se atoms by O atoms can achieve a bidirectional and wide-range (12×) tuning of thermal conductivity. The increase in specific heat and phonon group velocity is responsible for the thermal conductivity enhancement at high doping levels while that in phonon-phonon scattering rate is responsible for the thermal conductivity reduction at low doping levels. In all cases, acoustic phonons dominate the in-plane thermal transport behavior. These findings broaden our understanding of phonon transport and its control in ferroelectric semiconductorα-In2Se3.

Intervalley scattering induced significant reduction in lattice thermal conductivities for phosphorene

The thermal transport properties of buckled phosphorene (β-P) and antimonene (β-Sb) are investigated using first-principles methods. The large acoustic-optical phonon gaps of 3.8 THz and 2.2 THz enable the four-phonon interaction to play an important role in phonon scattering for both β-P and β-Sb. Considering the electron-phonon coupling, the lattice thermal conductivity can further undergo 84% decrease to 4.9 W mK^-1 for p-type β-P at n = 5 × 10¹³ cm^-2. By quantitatively describing the scattering probability of electrons in different paths combined with electron-phonon coupling matrix element analysis, it is found that multi-valley features of electronic band structure and strong electron-phonon coupling strength make electrons have strong intervalley scattering behavior in β-P. The former plays an important role in the energy conservation condition of the scattering process, and the latter determines the selection rule. Our work elucidates the contribution of higher-order phonon interactions as well as electron-phonon coupling effects to lattice thermal conductivity, and provides a new idea for finding materials with low lattice thermal conductivity induced by intervalley scattering.