Structural Stability, Thermodynamic and Transport Properties of Indium Under Two-Temperature Heating

Abstract

The density functional theory calculations were done to study the structural stability, thermodynamic and transport properties of indium in the two-temperature warm dense matter regime. The calculations show that in the case of “cold” lattice, the increasing electron temperature $T_e$ makes indium gradually change its structure from tetragonal with $c/a>$ 1 to tetragonal with  1 at $T_e>$ 5.8 kK. One of the intermediate phases in this transformation is the face centered cubic lattice (fcc, $c/a=$ 1). Under electron heating the parameter $c/a$ changes smoothly without any discontinuities and the change gets faster as $T_e$ grows. As shown by calculations, the electron–phonon coupling factor of indium is relatively small, $G\sim$ 5 $\cdot$ 10¹⁶ W/m³/K at 300 K. Its value weakly increases by about 40% as the temperature increases to 10 kK. Additionally, the static electric conductivity and electron thermal conductivity of indium under electron heating to 10⁴ K and a finite lattice temperature were calculated through the solution of the Boltzmann transport equation. The paper presents formulas that with good accuracy approximate the calculated dependencies of electric conductivity and thermal conductivity on $T_e$ and $T_i$. It is shown that the known semi-empirical formula for thermal conductivity, ${\kappa }_e\sim T_e$/$T_i$, overestimates ${\kappa }_e$ markedly at $T_e>$ 2 kK compared to the results obtained in the density functional calculations.