title: Local vibrations and negative thermal expansion in ZrW2O8.
abstract: We present an x-ray pair distribution function (XPDF) analysis and extended x-ray absorption fine structure (EXAFS) data for ZrW2O8 (10-500 K) with a focus on the stiffness of the Zr-O-W linkage. The XPDF is highly sensitive to W-Zr and W-W correlations, but much less so to O-O or W-O correlations. The Zr-W peak in the XPDF data has a weak temperature dependence and, hence, this linkage is relatively stiff and does not permit bending of the Zr-O-W link. We propose that the low energy vibrational modes that lead to negative thermal expansion involve correlated rotations of ZrO6 octahedra that produce large <111> translations of the WO4 tetrahedra, rather than a transverse motion of O atoms that imply a flexible Zr-O-W linkage.
authors.affiliation: Department of Physics, University of California, Santa Cruz, California 95064, USA.
authors.forename: F
authors.initials: F
authors.lastname: Bridges
authors.affiliation: Department of Physics, University of California, Santa Cruz, California 95064, USA.
authors.forename: T
authors.initials: T
authors.lastname: Keiber
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: P
authors.initials: P
authors.lastname: Juhas
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA and Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
authors.forename: S J L
authors.initials: SJ
authors.lastname: Billinge
authors.affiliation: Department of Physics, University of California, Santa Cruz, California 95064, USA.
authors.forename: L
authors.initials: L
authors.lastname: Sutton
authors.affiliation: Department of Physics, University of California, Santa Cruz, California 95064, USA.
authors.forename: J
authors.initials: J
authors.lastname: Wilde
authors.affiliation: Department of Chemistry, The City College of New York, The City University of New York, New York, New York 10031 USA.
authors.forename: Glen R
authors.initials: GR
authors.lastname: Kowach