Pressure induced superconductivity and electronic structure properties of scandium hydrides using first principles calculations

The electronic, vibrational and superconducting properties of scandium hydrides (ScH2 and ScH3) under pressure were studied using first-principles calculations. The results indicate that ScH2 and ScH3 are dynamically stable in the pressure ranges of 0-85 GPa and 46-80 GPa, respectively. The superconducting properties of ScH2 and ScH3 were investigated by employing Bardeen-Cooper-Schrieffer (BCS) theory, and this shows that the superconducting temperature of ScH2 initially increases exponentially and then reaches a maximum value of about 38.11 K at 30 GPa, while it remains constant under further compression. However, the superconducting behavior of ScH3 is not obvious under low pressure (P < 46 GPa), and it almost disappears under higher pressure, in agreement with experimental observations. Analysis of the energy band structures demonstrates that the distinct superconducting behaviors of ScH2 and ScH3 are related to the hybridization between the s-state of the H atom and the d-state of the Sc atom. The superconducting behavior of ScH2 follows the variation of the hybridization between the HO-s state and Sc-d state, while for ScH3, it is found that there is no density of states observed for HT or HO when the pressure is above 46 GPa. Analysis of the electronic structure of ScH2 was also performed to allow for further comprehension of the metallic behavior of ScH2 under pressure. This work may offer help to understand the mechanism of pressure-induced superconductivity in metal-hydride systems. © 2016 The Royal Society of Chemistry.