title: Conditions for Ta(IV)-Ta(IV) bonding in trirutile Li(x)MTa2O6.
abstract: Stabilization of Ta-Ta bonding in an oxide across a shared octahedral-site edge of a Ta2 dimer is not known. Investigation of Li insertion into the trirutile structure of MTa2O6 with M = Mg, Cr, Fe, Co, and Ni indicates that Ta-Ta bonding across the shared octahedral-site edge of the dimer can be stabilized by a reversible electrochemical reduction of Ta(V) to Ta(IV) for M = Cr, Fe, Co, and Ni but not for M = Mg. Chemical reduction of MTa2O6 by n-butyl lithium only reduced NiTa2O6 to any significant extent. With M = Fe, Co, or Ni, electrochemical formation of the Ta-Ta bonds is accompanied by a partial reduction of the Fe(II), Co(II), or Ni(II) to Fe(0), Co(0), or Ni(0). For M = Cr, two Li per formula unit can be inserted reversibly with no displacement of Cr(0). For M = Mg, no Mg(II) are displaced by Li insertion, but a solid-electrolyte interphase (SEI) layer is formed on the oxide with no evidence of Ta-Ta bonding. Stabilization of Ta-Ta bonding across a shared octahedral-site edge in a dimer appears to require significant hybridization of the Ta(V) 5d(0) and M 4s(0) states.
authors: Texas Materials Institute and ‡McKetta Department of Chemical Engineering and Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States.
authors: Asha
authors: A
authors: Gupta
authors: Preetam
authors: P
authors: Singh
authors: Hugo
authors: H
authors: Celio
authors: C Buddie
authors: CB
authors: Mullins
authors: John B
authors: JB
authors: Goodenough