Engineering the crystal structure and band gap of SrTeO4: inducing bonding changes and metallization through compression

Abstract

The impact of external pressure on the characteristics of SrTeO₄ has been thoroughly examined using density-functional theory calculations up to 100 GPa. It has been predicted that SrTeO₄ undergoes three phase transitions in the pressure range covered by this study. A first transition occurs at 2.5 GPa from the ambient-pressure orthorhombic structure (space group Pbcn) to another orthorhombic structure described by space group Pbcm. A second transition occurs at 7 GPa to a monoclinic structure described by space group P2₁/c and a third transition occurs at 80 GPa to another monoclinic structure described by space group P2₁/n. The phase transitions involve drastic changes in the atomic coordination of Sr and Te atoms. Additionally, we found that structural changes make the band-gap energy to rapidly decrease with pressure and drive metallization at 80 GPa. Moreover, we characterized the phonons and determined the compressibility of the different phases. We found that the low-pressure phase of SrTeO₄ exhibits a bulk modulus of 73.3(8) GPa. However, the bulk modulus is enhanced following the observed structural sequence, reaching a value of 175(6) GPa in the high-pressure phase found beyond 80 GPa. Finally, our study indicates that superconductivity is not induced by pressure in the metallic phase. Our findings provide fundamental insights into the high-pressure behavior of SrTeO₄.