Transformation characteristics of LaV/sub x/Nb/sub 1-x/O/sub 4/ compounds
X-ray diffractometry measurements were made as a function of temperature on a series of polycrystalline LaV/sub x/Nb/sub 1-x/O/sub 4/ compounds (0 < x < 0.3) to determine the effect of V substitutions on the temperature of the monoclinic/tetragonal transformation. The purpose was to provide basic information relating to crystal lattice stability in ABO/sub 4/ compounds that are either candidates or are appropriate models for candidate materials for hosting nuclear-waste ions. Partial substitution of V/sup 5 +/ on the Nb/sup 5 +/ site significantly lowers the tetragonal scheelite (I4/sub 1//a) to monoclinic fergusonite (I2/c) transformation, from 770/sup 0/K in LaNbO/sub 4/ to approximately 215/sup 0/K for LaV/sub 0/ /sub 25/Nb/sub 0/ /sub 75/O/sub 4/ (the solubility limit is close to x = 0.35). The transformation is displacive, of second order, involving two coupled order parameters. Heat capacity measurements on LaV/sub 0/ /sub 25/Nb/sub 0/ /sub 75/O/sub 4/ showed that the specific heat anamoly at the transformation point is extremely small. It is concluded that the two polymorphic forms of LaV/sub x/Nb/sub 1-x/O/sub 4/ have very nearly the same free energies over a substantial range of temperature below the transformation.
- Research Organization:
- Argonne National Lab., IL (USA)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 5920245
- Report Number(s):
- CONF-830375-3; ON: DE83014789
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
052002 -- Nuclear Fuels-- Waste Disposal & Storage
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400201* -- Chemical & Physicochemical Properties
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
DATA
EXPERIMENTAL DATA
INFORMATION
LANTHANUM COMPOUNDS
LATTICE PARAMETERS
MONOCLINIC LATTICES
NIOBATES
NIOBIUM COMPOUNDS
NUMERICAL DATA
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RARE EARTH COMPOUNDS
STABILITY
TEMPERATURE DEPENDENCE
TETRAGONAL LATTICES
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
DATA
EXPERIMENTAL DATA
INFORMATION
LANTHANUM COMPOUNDS
LATTICE PARAMETERS
MONOCLINIC LATTICES
NIOBATES
NIOBIUM COMPOUNDS
NUMERICAL DATA
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RARE EARTH COMPOUNDS
STABILITY
TEMPERATURE DEPENDENCE
TETRAGONAL LATTICES
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS