New high-pressure polymorph of In2S3 with defect Th3P4-type structure

The high pressure behavior of beta-In2S3 (14(1)/amd and Z=16) has been studied by in situ synchrotron radiation X-ray diffraction combined with diamond anvil cell up to 71.7 GPa. Three pressure-induced phase transitions are evidenced at similar to 6.6 GPa, similar to 11.1 GPa at room temperature and 35.6 GPa after the high-temperature annealing using a portable laser heating system. The new polymorph of In2S3 at 35.6 GPa is assigned to the denser cubic defect Th3P4 structure (I (4) over bar 3d and Z=5.333), whose unit-cell parameters are a=7.557(1) angstrom and V=431.6(2) angstrom(3). The Th3P4-type phase can be stable at least up to 71.7 GPa and cannot be preserved at ambient pressure. The pressure-volume relationship is well described by the second-order Birch-Murnaghan Equation of State, which yields B-o=63(3) GPa and B-o' = 4 (fixed) for the beta-In2S3 phase and B-o=87(3) GPa and B-o'=4 (fixed) for the defect Th3P4-type phase respectively. (C) 2013 Elsevier Inc. All rights reserved.