title: Phase transformation driven by valence electron concentration: tuning interslab bond distances in Gd5GaxGe4-x.
abstract: X-ray single crystal and powder diffraction studies on the Gd(5)Ga(x)()Ge(4)(-)(x)() system with 0 < or = x < or = 2.2 reveal dependence of interslab T-T dimer distances and crystal structures themselves on valence electron concentration (T is a mixture of Ga and Ge atoms). While the Gd(5)Ga(x)()Ge(4)(-)(x)() phases with 0 < or = x < or = 0.6 and valence electron concentration of 30.4-31 e(-)/formula crystallize with the Sm(5)Ge(4)-type structure, in which all interslab T-T dimers are broken (distances exceeding 3.4 A), the phases with 1 < or = x < or = 2.2 and valence electron concentration of 28.8-30 e-/formula adopt the Pu(5)Rh(4)- or Gd(5)Si(4)-type structures with T-T dimers between the slabs. An orthorhombic Pu(5)Rh(4)-type structure, which is intermediate between the Gd(5)Si(4)- and Sm(5)Ge(4)-type structures, has been identified for the Gd(5)GaGe(3) composition. Tight-binding linear-muffin-tin-orbital calculations show that substitution of three-valent Ga by four-valent Ge leads to larger population of the antibonding states within the dimers and, thus, to dimer stretching and eventually to dimer cleavage.
authors.affiliation: Ames Laboratory, Iowa State University, Ames, Iowa 500110, USA.
authors.forename: Yurij
authors.initials: Y
authors.lastname: Mozharivskyj
authors.forename: Wonyoung
authors.initials: W
authors.lastname: Choe
authors.forename: Alexandra O
authors.initials: AO
authors.lastname: Pecharsky
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Miller