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Title: Multiple high-temperature transitions driven by dynamical structures in NaI

Multiple, consecutive high-temperature transitions in NaI involving dynamical order and/or localization in the energy-momentum spectrum but not in the average crystal structure are revealed by lattice dynamics, x-ray lattice spacing, and heat capacity measurements. Distinctive energy-momentum patterns and lattice distortions indicate dynamical structures forming within randomly stacked planes, rather than the isolated point-defect-like intrinsic localized modes predicted. Transition entropies are accounted for by vibrational entropy changes and the transition enthalpies are explained by the strain energy of forming stacking-fault-like planar distortions deduced from x-ray diffraction peak shifts. The vibrational entropy of the dynamical structures stabilizes surrounding elastic distortions.
 [1] ;  [1] ;  [2] ;  [2] ;  [1]
  1. ORNL
  2. Santa Clara University, California
Publication Date:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 89; Journal Issue: 22
Research Org:
Oak Ridge National Laboratory (ORNL); Spallation Neutron Source
Sponsoring Org:
SC USDOE - Office of Science (SC)
Country of Publication:
United States