Effects of pressure-induced phase transitions on superconductivity in single-crystal Fe1.02Se

The temperature dependence of the ac susceptibility for single-crystalline Fe1.02Se has been measured at high pressures to 6.7 GPa. The superconducting transition temperature T-c displays a large increase from 7 to 30 K in the two-phase region at 0.5-1 GPa. Further increase in pressure results in the decrease in T-c which drops below 4.2 K at 6.7 GPa.