Refereed Articles
Frustrated Soft Modes and Negative Thermal Expansion in ZrW2O 8
  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.”  
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  Frustrated Soft Modes and Negative Thermal Expansion in ZrW2O 8.D. Cao, F. Bridges, G. Kowach, A. Ramirez, Phys. Rev. Lett. 2002, 89, 215902/1.