Ag13I4(AsO4)3: Synthesis, Crystal Structure and Ionic Conductivity

Ruby-red single crystals of Ag13I4(AsO4)3 were prepared for the first time by reacting a stoichiometric mixture of Ag2O, AgI and As2O3 at elevated oxygen pressure of 120 MPa and at a temperature of 350 ◦C. The polyhedral crystals belong to the monoclinic space group P21/m with a = 9.247(1), b = 7.152(1), c = 17.674(2) Å, β = 91.492(2)◦, and Z = 2. The structure is fully ordered and was solved by Direct Methods, and refined on single crystal diffraction data (10376 observed reflections, R1 = 3.28%). The crystal structure is built up of two two-dimensional interlocked partial structures, one consisting of silver and iodine ions, the other of silver and arsenate(V) ions. The slabs extend in the ac plane, and the Ag–I framework is linked to the AsO43− units by Ag–O contacts. The silver–oxygen interactions perturb the tetrahedron of the arsenate group, resulting in As–O distances ranging from 1.670 to 1.697 Å, and angles varying from 107.3 to 112.1◦. Pure Ag13I4(AsO4)3 is a solid ion conductor with a r. t. conductivity of 6.4×10−6 Ω−1 cm−1 at 30 ◦C. The activation energy for silver ion conduction is 0.41 eV in the temperature range from 30 to 130 ◦C.