PRESSURE-INDUCED AMORPHIZATION OF COVELLITE, CUS

CuS, or covellite (hexagonal symmetry), was compressed in a diamond an vil cell at room temperature up to a pressure of 45 GPa, and studied u sing x rays from both a Mo K-alpha source and a synchrotron. The x-ray diffraction spectrum of CuS disappears by about 18 GPa. The presence of Cu fluorescence lines in all spectra and the reappearance of diffra ction lines upon decompression confirm that CuS: undergoes reversible pressure-induced amorphization at this pressure. A third-order Birch-M urnaghan equation of state fit to the diffraction data below 11 GPa yi elds a bulk modulus of 89+/-10 GPa with a pressure derivative of -2+/- 2 for covellite. Further compression up to 45 GPa shows three to four diffraction lines of very low intensity, implying some high pressure ' 'ordering'' of the amorphous phase. The Raman spectra obtained indicat e that the changes in structure are probably due to the twisting or th e distortion of covalently bonded CuS4-CuS4 units in different directi ons. (C) 1996 American Institute of Physics.