title: Frustrated soft modes and negative thermal expansion in ZrW2O8.
abstract: Negative thermal expansion (NTE) in cubic ZrW2O8 has generated much interest due to its large, isotropic, and temperature independent behavior. Here, x-ray absorption fine structure data are presented for various atom pairs, providing evidence that the low-energy modes causing NTE correspond to the correlated vibrations of a WO4 tetrahedron and its three nearest ZrO6 octahedra. This involves translations of the WO4 as a rigid unit along each of the four <111> axes. The interconnectivity of these modes prevents an anisotropic soft mode from developing, a new geometrical phenomenon that we call the "frustrated soft mode."
authors.affiliation: Physics Department, University of California, Santa Cruz, California 95064, USA.
authors.forename: D
authors.initials: D
authors.lastname: Cao
authors.forename: F
authors.initials: F
authors.lastname: Bridges
authors.forename: G R
authors.initials: GR
authors.lastname: Kowach
authors.forename: A P
authors.initials: AP
authors.lastname: Ramirez