First-principles study of the high-pressure phase transition inZnAl2O4andZnGa2

In this work we present a first-principles density functional study of the electronic, vibrational, and structural properties of ${\text{ZnGa}}_{2}{\text{O}}_{4}$ and ${\text{ZnAl}}_{2}{\text{O}}_{4}$ spinel structures. Here we focus our study in the evolution of the structural properties under hydrostatic pressure. Our results show that ${\text{ZnGa}}_{2}{\text{O}}_{4}$ under pressure has a first-order phase transition to the marokite $({\text{CaMn}}_{2}{\text{O}}_{4})$ structure, which is in good agreement with recent angle-dispersive x-ray diffraction experiments. We also report a similar study for the ${\text{ZnAl}}_{2}{\text{O}}_{4}$ spinel; we found that this compound under pressure has a first-order phase transition to the orthorhombic ${\text{CaFe}}_{2}{\text{O}}_{4}$-type structure. Our results in both compounds support, under nonhydrostatic condition, the possibility of a second-order phase transition from the cubic spinel to the tetragonal spinel as reported experimentally in ${\text{ZnGa}}_{2}{\text{O}}_{4}$.