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

Abstract

Ruby-red single crystals of Ag 13 I 4 (AsO 4 ) 3 were prepared for the first time by reacting a stoichiometric mixture of Ag 2 O, AgI and As 2 O 3 at elevated oxygen pressure of 120 MPa and at a temperature of 350 ◦ C. The polyhedral crystals belong to the monoclinic space group P2 1 /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 AsO 4 3 − 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 Ag 13 I 4 (AsO 4 ) 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