X-RAY-POWDER DIFFRACTION OF AG2TE AT TEMPERATURES UP TO 1123-K

X-ray powder diffraction was performed on beta-Ag2Te at room temperature, on ion conducting alpha-Ag2Te at 523 K, 723 K and 923 K respectively and on gamma-Ag2Te at 1123 K. Rietveld profile refinement of beta-Ag2Te confirmed the space group P2(1)/c and the positional parameters of the model of Frueh (Z. Kristallogr. 112 (1959) 44-52). For the alpha-modification in space group Fm3mBAR, best results were obtained for a model with a statistical distribution of Ag ions: about 60% of the available Ag ions were placed into 32f(xxx) positions around the tetrahedral 8c(1/4 1/4 1/4) sites and the remainder on the 48i(xx1/2) positions. The probability density function (PDF) calculated with these formal structure parameters suggests next neighbour jumps of Ag ions via the 48i sites. The first structure refinement of gamma-Ag2Te showed it to crystalize in space group Im3mBAR and to be iso-structural to alpha-AgI. Third order anharmonic coefficients of the temperature factor of the Ag ions could be refined from our X-ray powder data. Corresponding PDF maps show Ag-densities bridging next nearest as well as second next nearest neighbours.