Multiple high-temperature transitions driven by dynamical structures in NaI

Journal Article · Wed Jan 01 00:00:00 EST 2014 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.89.224106· OSTI ID:1156746

Manley, Michael E ^[1]; Jeffries, Jason R ^[1]; Lee, Hohyun ^[2]; Zabalegui, Aitor ^[2]; Abernathy, Douglas L ^[1]

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1. ORNL
2. Santa Clara University, California

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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1156746
• Journal Information: Physical Review B, Vol. 89, Issue 22; ISSN 1098--0121
• Country of Publication: United States
• Language: English