First principle calculations of structural and electronic properties of pyrochlore Y2Ru2O7 and Y1-M Ru2O7−δ (M=Mg, Ca, Sr, Ba, Zn, Cd and Hg)

The electronic structural and electronic properties of pyrochlore Y2Ru2O7 (YRO) and Y1-xMxRu2O7−δ (M = Mg, Ca, Sr, Ba, Zn, Cd and Hg) were investigated using first-principle calculation based on GGA + U and HSE06 hybrid functional. The schematic energy level diagram of YRO was drawn, and its band gap was found to locate in π* antibonding orbital, dominated by Ru-4d electrons. RuO6 octahedrons in YRO undergo a compressing trigonal distortion, with a local symmetry group of D3d, which is quite different from RuO2 and perovskite ruthenium oxide. When Y is substituted by divalent cation M (MY), O vacancies can achieve low formation energy and introduce the MY-VO and 2MY-VO complex. Further calculation showed that MY-VO complex in YRO can induce an impurity energy level into forbidden band, and narrow the band gap. As a result, high electrical conductivity of Y1-xMxRu2O7−δ is expected, and MY-VO complex may be the origin of electrocatalytic activity in Y1-xMxRu2O7.