Origin of positive/negative effects on pressure-dependent thermal conductivity: the role of bond strength and anharmonicity

Abstract

Pressure-dependent thermal conductivity is leveraged to enhance device performance in electronic materials. However, the unclear physical mechanisms greatly limit further development of complex energy materials. We propose the crucial role of atom size and chemical bonds in thermal and thermoelectric properties by considering the pressure- and element-dependence anharmonicity of XSe (X = Be, Mg, Ca) compounds across Fmm and F3m phases. The weak anharmonicity and bond strength lead to a positive effect through ionic-driven harmonic coulombic interactions, and the strong anharmonicity and bond strength result in a negative effect due to covalent-driven electrostatic interactions. Furthermore, the pressure-dependent thermal conductivity of F3m CaSe does not decrease uniformly due to the competition between positive and negative effects. Combined with the complex electronic structures and weak coupling between acoustic phonons and carriers, this feature endows F3m CaSe with promising electrical transport properties. Understanding the origins of pressure-dependent thermal conductivity is important for the future design of superior materials and provides insight into experimental observation predicting behavior.