Darstellung und Kristallstruktur der Hochdruckphase AgAlS2-II / Preparation and Crystal Structure of the High-pressure Phase AgAlS2-II

AgAlS 2 -I with chalcopyrite structure transforms at 25 kbar and 300°C to the new highpressure phase AgAlS 2 -II. The crystal structure of AgAlS 2 -II is trigonal, space group P3ml, with a= 3,50 Å, c = 6,84 Å and Z = 1. The structure is based on a hexagonally close packed arrangement of sulfur atoms with aluminium atoms in octahedral sites and silver atoms in tetrahedral sites. The AgS 4 -tetrahedra are considerably distorted, giving a coordination number 3 + 1 for the silver atoms.