Crystal structure, electrical resistivity, and X-ray photoelectron spectroscopy of BaAg2As2

The ternary arsenide BaAg2As2 has been prepared by reaction of the elements at 850 °C. Single-crystal and powder X-ray diffraction analysis revealed that it adopts the ThCr2Si2-type structure (Pearson symbol tI10, space group I4/mmm, Z=2, a=4.6025(3) Å, c=10.8672(6) Å at 295 K) featuring [Ag2As2] layers interconnected by homoatomic As–As bonds along the c-direction. Band structure calculations indicate no gap at the Fermi level, and support the occurrence of strong As–As and weak Ag–Ag bonding. The asymmetric lineshape and the absence of a BE shift in the Ag 3d5/2 core-line peak relative to the element suggest delocalization of the Ag valence electrons. A significant negative BE shift (1.0 eV) in the As 3d5/2 core-line peak relative to the element confirms the presence of anionic As atoms. A reversible transition is observed at 175 K in the electrical resistivity, and is probably related to a structural phase transition.