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Title: High-temperature phase transformation and topochemical nature in ferroelastic (NH{sub 4}){sub 2}SO{sub 4}

The electrical conductivity of ferroelastic ammonium sulfate (NH{sub 4}){sub 2}SO{sub 4} revealed an anomaly at around 130 °C (=403 K, T{sub P}) on heating with large and irreversible thermal hysteresis through thermal cycle. Ferroelastic domain walls and surface morphology of (NH{sub 4}){sub 2}SO{sub 4} were investigated by hot-stage polarizing microscopy. Structural phase transition from an orthorhombic ferroelastic phase to a hexagonal paraelastic phase was not identified at T{sub P} upon heating. On further heating above T{sub P}, microscopic spots appeared and grew on the crystal surface, suggesting that the high-temperature anomaly at T{sub P} was an indication of an onset of thermal decomposition controlled by topochemical factors. The increase of electrical conductivity above T{sub P} was attributed to proton migration. - Graphical abstract: Surface morphology of the (100) face of (NH{sub 4}){sub 2}SO{sub 4} on heating, showing chemical reaction at the surface. - Highlights: • We investigate the high-temperature phase transformation of ammonium sulfate. • The increasing conductivity upon heating is attributed to proton migration. • Structural phase transition from orthorhombic to hexagonal phase is not confirmed. • High-temperature anomaly is related to an onset of thermal decomposition. • The nature of the high-temperature anomaly is topochemical controlled by defects.
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Nano Science and Engineering, Center for Nano Manufacturing, Inje University, Gimhae 621-749 (Korea, Republic of)
  2. Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of)
  3. Department of Physics, Hallym University, Chuncheon 200-702 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22334170
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 212; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMMONIUM SULFATES; CRYSTALS; DEFECTS; ELECTRIC CONDUCTIVITY; HYSTERESIS; MICROSCOPY; ORTHORHOMBIC LATTICES; PHASE TRANSFORMATIONS; PROTONS; PYROLYSIS