First-principles investigation of Sc-III/IV under High Pressure

TL;DR

This study uses first-principles calculations to explore the high-pressure phases of scandium, identifying potential structures for phases III and IV and examining their superconducting properties, aligning well with experimental data.

Contribution

It provides a systematic prediction of scandium's high-pressure phases and proposes specific structures for phases III and IV, enhancing understanding of its phase diagram.

Findings

Identified candidate structures for Sc-III and Sc-IV phases.

Predicted superconducting transition temperatures consistent with experiments.

Reproduced known allotropes and explained previously unresolved phases.

Abstract

Using ab initio evolutionary structure prediction method in conjunction with density functional theory, we performed a systematic investigation on the structural transition of elemental scandium under pressure up to 250 GPa. Our prediction successfully reproduced several allotropes which have been reported in the previous literature, including the Sc-I, Sc-II and Sc-V. Moreover, we observed a series of energetically degenerate and geometrically similar structures at 110-195 GPa, which are likely to explain the unsolved phases III and IV reported by Akahama [Phys. Rev. Lett.,94, 19, 195503, (2005)]. A detailed comparison on powder X-ray diffraction pattern (PXRD) suggested that the Ccca-20 phase may account for the observed Sc-III, while Sc-IV is likely to be explained by a mixture of multiple energetically competing structures. We also used the candidate Sc-III structure as the model system to explore its superconducting behavior under pressures between 80-130 GPa. The predicted superconducting transition temperature Tc values are in satisfactory agreement with previous experimental results.