title: "Nanoscale zippers" in Gd5(SixGe(1-x))4: symmetry and chemical influences on the nanoscale zipping action.
abstract: One critical parameter influencing the structural nature of the phase transitions in magnetocaloric materials Gd5(SixGe(1-x))4 is the Si/Ge ratio (x/1-x), because transition temperatures and structures depend crucially on this value. In this study, single-crystal X-ray diffraction indicates that Si and Ge atoms are neither completely ordered nor randomly mixed among the three crystallographic sites for these elements in these structures. Ge atoms enrich the T sites linking the characteristic slabs in these structures, while Si atoms enrich the T sites within them. Decomposition of the total energy into site and bond energy terms provides a rationale for the observed distribution, which can be explained by symmetry and electronegativity arguments. For any composition in Gd5(SixGe(1-x))4, a structure map is presented that will allow for a rapid assessment of the specific structure type.
authors.affiliation: Department of Chemistry, Department of Materials Science and Engineering, and Ames Laboratory, US Department of Energy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Wonyoung
authors.initials: W
authors.lastname: Choe
authors.forename: A O
authors.initials: AO
authors.lastname: Pecharsky
authors.forename: Michael
authors.initials: M
authors.lastname: Wörle
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Miller