Electronic, Structural, Elastic, and Thermodynamic Properties of X2TiBr6 (X = Li and Na) under Pressure: A DFT Investigation

Abstract

We investigate the electronic, structural, elastic, and thermodynamic properties of X₂TiBr₆ (X = Li and Na) under pressure using the DFT calculations as implemented in the Quantum Espresso code. Generalized gradient approximation in the Perdew–Burke–Ernzerhof (PBE) form is used in this work. The calculated lattice parameters are 9.864 and 9.959 Å for Li₂TiBr₆ and Na₂TiBr₆, respectively. The structure bands of the Li₂TiBr₆ and Na₂TiBr₆ compounds indicate energy band gaps of 0.92 and 1.0 eV, respectively. Their value increases with increasing ionic radius from Li to Na. The elastic constants, bulk modulus, shear modulus; Young’s modulus, Pugh’s ratio, and Poisson’s ratio have also been computed. The studied compounds are thermodynamically stable, and their stability decreased with the increase of atomic radius. Pugh’s and Poisson’s ratios that were calculated show that Li₂TiBr₆ and Na₂TiBr₆ are ductile compounds. The results also show that the heat capacity at high temperatures of the two compounds was found to be 224 J mol^–1 K^–1.