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)

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 compou...

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Bibliographic Details
Published in:Journal of solid state chemistry 1993-07, Vol.105:1
Main Authors: Takahashi, Kazuo, Fujino, Takeo, Morss, L.R.
Format: Article
Language:English
Subjects:
360202 - Ceramics, Cermets, & Refractories- Structure & Phase Studies
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
MATERIALS SCIENCE
MATHEMATICAL MODELS
PHASE STUDIES
PHYSICAL PROPERTIES
POINT DEFECTS
RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
REACTION HEAT
STOICHIOMETRY
STRONTIUM COMPOUNDS
STRONTIUM URANATES
THERMODYNAMIC PROPERTIES
TRIGONAL LATTICES
URANATES
URANIUM COMPOUNDS
VACANCIES
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Summary: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.
ISSN:0022-4596
1095-726X
DOI:10.1006/jssc.1993.1211