Crystal chemical and thermodynamic study on CaUO[sub 4[minus]x], (Ca[sub 0. 5]Sr[sub 0. 5])UO[sub 4[minus]x], and [alpha]-SrUO[sub 4[minus]x] (x = 0 [approximately] 0. 5)

Journal Article · Thu Jul 01 04:00:00 EDT 1993 · Journal of Solid State Chemistry; (United States)

DOI:https://doi.org/10.1006/jssc.1993.1211· OSTI ID:5726591

Takahashi, Kazuo ^[1]; Fujino, Takeo ^[2]; Morss, L R ^[3]

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1. Japan Atomic Energy Research Inst., Ibaraki (Japan)
2. Tohoku Univ., Sendai (Japan)
3. Argonne National Lab., IL (United States)

A crystallographic and thermochemical study of CaUO[sub 4[minus]x], (Ca[sub 0.5]Sr[sub 0.5])UO[sub 4[minus]x], and [alpha]-SrUO[sub 4[minus]x] with x values ranging from nearly 0 to 0.5 was carried out. As the crystal radius of the divalent cations increases, a(rhomb) of nearly stoichiometric compounds increases, accompanied by an increase in the cell volume, whereas [alpha](rhomb) decreases. With nonstoichiometry, the lattice parameters of (Ca[sub 0.5]Sr[sub 0.5])UO[sub 4[minus]x] and [alpha]-SrUO[sub 4[minus]x] discontinuously change at 4 [minus] x = 3.79 and 3.77, respectively, although each compound is a single phase in the entire range from 4 [minus] x = 4.00 to 3.50. For CaUO[sub 4[minus]x], the products were two-phase mixtures between 4 [minus] x = 3.98 and 3.70. These crystal structures are discussed taking into account the lattice parameters and interatomic distances. In the nonstoichiometric crystals, oxygen vacancies exist on the O[sub II] sites but not on the O[sub I] sites. The enthalpy of formation of [alpha]-SrUO[sub 4[minus]x] was measured for several specimens with different x values by solution calorimetry, and was expressed in a second-order polynomial of x by least-squares calculation. This quantity and its derivative, i.e., partial molar enthalpy of oxygen, suggest the change of defect species with x and the existence of repulsive vacancy-vacancy interaction. 35 refs., 11 figs., 5 tabs.

• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 5726591
• Journal Information: Journal of Solid State Chemistry; (United States), Journal Name: Journal of Solid State Chemistry; (United States) Vol. 105:1; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600 -- Radiation Chemistry
ACTINIDE COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALORIMETRY
CRYSTAL DEFECTS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DATA ANALYSIS
ENTHALPY
FORMATION HEAT
LATTICE PARAMETERS
MATHEMATICAL MODELS
PHASE STUDIES
PHYSICAL PROPERTIES
POINT DEFECTS
REACTION HEAT
STOICHIOMETRY
STRONTIUM COMPOUNDS
STRONTIUM URANATES
THERMODYNAMIC PROPERTIES
TRIGONAL LATTICES
URANATES
URANIUM COMPOUNDS
VACANCIES