X-ray powder diffraction of Ag2Te at temperatures up to 1123 K

Abstract X-ray powder diffraction was performed on β -Ag 2 Te at room temperature, on ion conducting α -Ag 2 Te at 523 K, 723 K and 923 K respectively and on γ -Ag 2 Te at 1123 K. Rietveld profile refinement of β -Ag 2 Te confirmed the space group P 2 1 / c and the positional parameters of the model of Frueh (Z. Kristallogr. 112 (1959) 44–52). For the α -modification in space group Fm unk m , best results were obtained for a model with a statistical distribution of Ag ions: about 60% of the available Ag ions were placed into 32 f ( xxx ) positions around the tetrahedral 8 c (¼ ¼ ¼) sites and the remainder on the 48 i ( xx ½) positions. The probability density function (PDF) calculated with these formal structure parameters suggests next neighbour jumps of Ag ions via the 48 i sites. The first structure refinement of γ -Ag 2 Te showed it to crystalize in space group Im unk m and to be iso-structural to α -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.