Some Factors Governing Ag+ and Cu+ Low Coordination in Chalcogenide Environments

The high-pressure behavior of semiconducting cadmium thiogallate CdGa2Se4 with the defect chalcopyrite structure (I , Z=2) is studied by in situ angle-dispersive synchrotron X-ray powder diffraction and optical reflectivity measurements in a diamond anvil cell at room temperature. At 21 GPa an order-disorder phase transition to the rock-salt structure (F 3m, Z=4) occurs. Upon decompression, the metallic NaCl-type polymorph transforms into zinc-blende (Fm m, Z=4) at pressures of 7.5-4 GPa. The recovered metastable semiconducting material is of the zinc-blende type