Beschreibung:
AbstractAg8I2(CrO4)3 has been synthesized by solid state reaction, starting from stoichiometric mixtures of Ag2O, AgI and Cr2O3, at elevated oxygen pressures. The compound crystallizes in the hexagonal space group P63/m, with the unit cell dimensions a = 9.4474(4) Å, c = 10.2672(4) Å, γ = 120°, V = 793.61(6) Å3, and Z = 6. The crystal structure was solved by direct methods and refined, basing on single crystal diffraction data (815 independent reflections, R1 = 2.45 %). The structure is fully ordered. The CrO42– ions are arranged in the mode of an hcp packing. Such a building principle is providing channels of face sharing octahedral voids. In the case of the title compound, there are three of such channels in the unit cell. Two of them accommodate two iodine atoms and one silver each, with iodine occupying the octahedral voids, and silver centering the triangular faces connecting the octahedra. Thus, for silver a trigonal bipyramidal coordination by three oxygen and two iodine ions result. In the third column of face sharing octahedra, silver is in the centre of the octahedra. The remaining silver atoms are located in the tetrahedral voids, between the CrO42– ions. According to the results of impedance measurements, Ag8I2(CrO4)3 is a silver ion conductor. The compound shows an increase in the ionic conductivity in the temperature range from 25 to 175 °C, and has a silver ion conductivity of 6.5 × 10–4 Ω–1·cm–1 at 30 °C. The activation energy for silver ion conduction is 0.21 eV, in the temperature range from 25 to 50°.