A first-principle study on the phase transition, electronic structure, and mechanical properties of three-phase ZrTi₂ alloy under high pressure*

Abstract

We employed density-functional theory (DFT) within the generalized gradient approximation (GGA) to investigate the ZrTi₂ alloy, and obtained its structural phase transition, mechanical behavior, Gibbs free energy as a function of pressure, P-V equation of state, electronic and Mulliken population analysis results. The lattice parameters and P-V EOS for α, β and ω phases revealed by our calculations are consistent with other experimental and computational values. The elastic constants obtained suggest that ω-ZrTi₂ and α-ZrTi₂ are mechanically stable, and that β-ZrTi₂ is mechanically unstable at 0 GPa, but becomes more stable with increasing pressure. Our calculated results indicate a phase transition sequence of α → ω → β for ZrTi₂. Both the bulk modulus B and shear modulus G increase linearly with increasing pressure for three phases. The G/B values illustrated good ductility of ZrTi₂ alloy for three phases, with ω<α<β at 0 GPa. The Mulliken population analysis showed that the increment of d electron occupancy stabilized the β phase. A low value for B '₀ is the feature of EOS for ZrTi₂ and this softness in the EOS is representative of pressure induced s-d electron transfer.