STRUCTURE OF FES UNDER HIGH-PRESSURE

Compression behavior of FeS at room temperature up to 15 GPa is invest igated using a combination of a synchrotron white X-ray source and a l arge volume press (MAX80). Two high pressure phase transitions at 3 an d 7 GPa are reconfirmed. The high pressure phase between 3 and 7 GPa c an be explained by a MnP type related structure. From 26 diffraction l ines at 10.30 GPa, unit cell dimensions of the higher pressure phase, of which the crystal structure has been unknown, are determined to be a = 8.044(3)Angstrom, b = 5.611(2)Angstrom, c = 6.433(4)Angstrom, beta = 93.11(4)degrees and Z = 12 for a monoclinic system. Possible space group for the cell is P2(1) or P2(1)/m, and there are multi-sites for iron atoms in the cell. The cell dimensions show that the higher press ure phase still has a NiAs type framework in the structure. The high p ressure phase is about 6% denser than the MnP type phase at 7 GPa, and is estimated to be 12% denser than the troilite phase at ambient cond ition. (C) 1997 Elsevier Science Ltd. All rights reserved.