Pressure effects on energy gaps and phase transitions in ZnAl2Se4

Abstract

The full potential linear augmented wave method has been used for an ab-initio study of structural, electronic and high pressure phase transformation features of ZnAl2Se4. The exchange and correlation potential (XC) was calculated using the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and the modified GGA due to Engel–Vosko (EV-GGA). The geometry optimization was performed by calculating the total energy as a function of the three variables u, c/a and V. Using the sets of data obtained we determined the equilibrium volume, V0, the bulk modulus, B0, and the pressure derivative of the bulk modulus, B0′. The results show that ZnAl2Se4 is a direct wide band gap semiconductor at ambient conditions (P = 0, T = 0). With increasing hydrostatic pressure of the unit cell (i.e., with decreasing size) both the direct (Γ—Γ) and the indirect (Γ—H) energy gaps first increase and at a pressure of 9.2 GPa both gaps become equal and start decreasing as the pressure increases further but with a change in the nature of the energy band gap from direct to indirect. With increasing pressure a transition from tetragonal to spinel phase has been observed at a pressure of 3 GPa.