High pressure investigation of the tetragonal distortion and the anion displacement in AgGaX2 (X=S, Se, Te)

High pressure Rietveld refinement is reported for three chalcopyrites AgGaX2 (X=S, Se, and Te). It is found that the tetragonal distortion (eta=c/a) decreases with increasing pressure but the anion displacement parameter (u-parameter) remains constant within experimental error. The chemical trend of these two structural parameters in these three chalcopyrites is compared with the high pressure results. The chemical trend of the tetragonal distortion is partly understood by the pressure effect. However, the chemical trend of the u-parameter is guile different from the pressure effect.