Partial anion exchange in Ag_(23)Te_(12)X: The solid solutions Ag_(23)Te_(12)Cl_(1-x)Br_x, Ag _(23)Te_(12)Br_(1-y) and Ag_(23)Te _(12)Cl_(1-z)i_z

摘要

X-ray powder diffraction, EDX and DSC measurements were performed in order to determine the structural and thermal properties of the solid solutions of Ag_(23)Te_(12)Cl_(1-x)Br_x,Ag _(23)Te_(12)Br_(1-y)I_y and Ag _(23)Te_(12)Cl_(1-z)I_z. A complete solid solution exists between the two ternary end members Ag_(23)Te _(12)Cl and Ag_(23)Te_(12)Br, whereas the substitution of bromine by iodine can only be observed up to y = 0.3 in Ag _(23)Te_(12),Br_(1-y)I_y under thermodynamically controlled synthesis conditions. Even chlorine can. be partially substituted by small amounts of iodine up to a certain extend. Temperature dependent single crystal structure determinations of crystals with the nominal composition Ag_(23)Te_(12)Cl_(0.95)I _(0.05) substantiated the significant influence of the iodine intake on the lattice parameters of the pseudo-tetragonal orthorhombic system, especially at low temperatures. A systematic deviation from the 1:1 ratio of the a and b lattice parameter (pseudo-tetragonal ratio) was observed upon cooling, which could not be detected in the case of the ternary compounds. X-ray powder diffraction experiments gave a first hint on the non-stoichiometry of this set of materials and all compounds show peritectic decomposition to binary phases at temperatures slightly above 680 K.