Synthesis, structure and properties of Ag_2PdO_2

摘要

The first silver palladium oxide, Ag_2PdO_2, was synthesised from a co-precipitated oxide precursor by annealing at 423-823 K, applying an oxygen pressure of 73 MPa. The crystal structure has been determined from X-ray and neutron powder diffraction data. The new compound crystallises in space group Immm. The lattice constants as determined from X-ray powder diffraction are a = 4.55523(5) A, b = 3.00803(3) A and a = 9.8977(1) A. The crystal structure constitutes a new structure type showing some features in common with the Li_2CuO_2-type. Palladium is found in a nearly square planar arrangement while silver has an almost linear co-ordination. The overall structure can be considered as a rocksalt defect structure. Ag_2PdO_2 is diamagnetic and semiconducting. The band gap, estimated from conductivity measurements in the temperature range of 240-300 K, is 0.18(2) eV.