Search for promising structures and superconductivity in high-pressure Sr through first-principles calculations.

In the high-pressure phases of Sr, the Sr-V phase is considered an incommensurate host–guest structure. However, just as a low-temperature phase Ba-VI exists in the pressure region of the Ba-IV phase of high-pressure Ba, Sr also has a Sr-VI phase on the low-temperature region of the Sr-V phase according to experiments. We investigated the pressure range from 40 to 2400 GPa using first-principles calculations and found a group of promising candidate structures for the Sr-VI phase. At higher pressures, the lowest-enthalpy structure became hexagonal close-packed (hcp) around 160 GPa and is consistent with experiments for the Sr-VII phase, and the hcp structure transformed to a double hcp (dhcp) structure around 1000 GPa, and then, the dhcp structure changed to a face-centered cubic structure around 2200 GPa. The superconducting state remained intact through these structural phase transitions, although with a decreasing Tc with increasing pressure. [ABSTRACT FROM AUTHOR]