SINGLE-CRYSTAL X-RAY-DIFFRACTION STUDY ON STRUCTURAL-CHANGE OF AGGAS2WITH INCREASING PRESSURE

Single-crystal X-ray diffraction study under high pressures has been c arried out on silver thiogallate, AgGaS2, to investigate the phase tra nsition at about 42 kbar. The crystal of AgGaS2 is tetragonal with the space group I42dBAR having the cell dimensions a = 5.7603(6) and c = 10.299(2) angstrom under the ambient pressure. The high-pressure form has a similar unit cell to that of the ambient pressure form. The diff raction pattern around the [221BAR] zone axis at 47 kbar indicated tha t the high pressure form has weak but clear hhl reflections which do n ot satisfy the systematic absence condition, 2h + l = 4n, for the spac e group I42dBAR. It has been concluded that the diamond glide planes p arallel to {110} present in the ambient pressure form disappear in the high pressure form.