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

The ternary arsenide BaAg{sub 2}As{sub 2} has been prepared by reaction of the elements at 850 Degree-Sign C. Single-crystal and powder X-ray diffraction analysis revealed that it adopts the ThCr{sub 2}Si{sub 2}-type structure (Pearson symbol tI10, space group I4/mmm, Z=2, a=4.6025(3) A, c=10.8672(6) A at 295 K) featuring [Ag{sub 2}As{sub 2}] 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 3d{sub 5/2} 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 3d{sub 5/2} 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. - Graphical abstract: BaAg{sub 2}As{sub 2} adopts a ThCr{sub 2}Si{sub 2}-type structure with As-As pairs and undergoes a transition at 175 K in its electrical resistivity. Highlights: Black-Right-Pointing-Pointer BaAg{sub 2}As{sub 2} fills the gap within the BaM{sub 2}As{sub 2} series containing 4d metals. Black-Right-Pointing-Pointer [Ag{submore » 2}As{sub 2}] layers are linked by As-As pairs. Black-Right-Pointing-Pointer XPS studies support the assignment of monovalent Ag and anionic As atoms. Black-Right-Pointing-Pointer An anomaly is observed at 175 K in the electrical resistivity.« less