Studies of layered uranium(VI) compounds. III. Structural investigations of hydrogen uranyl phosphate and arsenate tetrahydrates below the respective transition temperatures of 274 and 301/sup 0/K

Journal Article · Mon Sep 01 04:00:00 EDT 1980 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(80)90216-9· OSTI ID:6811362

Shilton, M G; Howe, A T

The layered hydrates HUO/sub 2/PO/sub 4/.4H/sub 2/O (HUP), and HUO/sub 2/AsO/sub 4/.4H/sub 2/O (HUAs), which are proton-conducting solid electrolytes above the conductivity transitions at 274 and 301/sup 0/K, respectively, have been shown, using powder x-ray diffraction, to change from tetragonal to orthorhombic symmetry below these temperatures. For HUP the unit-cell dimensions were a = 6.985(5) and c = 17.45(1) A at 290/sup 0/K, and a = 6.966(5), b = 7.004(5), and c = 17.43(1) A at 260/sup 0/K. The values for HUAs were a = 7.150(2) and c = 17.608(5) A at 305/sup 0/K, and a = 7.128(2), b = 7.168(2), and c = 17.613(5) A at 293/sup 0/K. The enthalpies of these displacive-type transitions were found from differential scanning calorimetry to be less than 0.5 kJ per mole of water for both compounds. Such a small value indcates that the rigid-like water lattices existing below the transitions do not become liquid-like above the transitions. The infrared spectra of HUP and HUAs both above the transitions, and down to 80/sup 0/K, showed clear evidence of the presence of H/sub 3/O/sup +/ ions, showing that the conductivity transitions are not caused by a loss of carriers. Rather, the antiferroelectric ordering, known to exist for HUAs, would appear to cause the conductivity drop. Upon this indication of ordering within the water layers, two possible related H-bond ordered structures have been proposed which are consistent with the observed twinning behavior and cell symmetry. The same ordered structures are suggested for HUP from our observations of the twinning behavior.

• Research Organization: Univ. of Leeds, England
• OSTI ID: 6811362
• Journal Information: J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 34:2; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400702* -- Radiochemistry & Nuclear Chemistry-- Properties of Radioactive Materials
ACTINIDE COMPOUNDS
ARSENATES
ARSENIC COMPOUNDS
CALORIMETRY
CHARGED PARTICLES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ENTHALPY
HYDRATES
HYDROGEN COMPOUNDS
INFRARED SPECTRA
IONS
LATTICE PARAMETERS
LAYERS
LOW TEMPERATURE
MEDIUM TEMPERATURE
MOLECULAR IONS
ORTHORHOMBIC LATTICES
OXONIUM IONS
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
PHYSICAL PROPERTIES
SCATTERING
SPECTRA
STRUCTURAL CHEMICAL ANALYSIS
TETRAGONAL LATTICES
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
TWINNING
URANIUM COMPOUNDS
URANYL COMPOUNDS
URANYL PHOSPHATES
X-RAY DIFFRACTION