Crystal structure and stoichiometry of the Ca/sub 2+x/Nd/sub 8-x/(SiO/sub 4/)/sub 6/O/sub 2-1/2x/ system

Conference · Mon Jun 01 00:00:00 EDT 1981

OSTI ID:6232358

Fahey, J A; Weber, W J

A systematic study of Ca/sub 2+x/Nd/sub 8-x/(SiO/sub 4/)/sub 6/O/sub 2-1/2x/, one of the mineral-like phases formed by the rare earths in the supercalcine-ceramic nuclear waste forms, has been undertaken. Until now, the structure and stoichiometry of this apatite phase has only been inferred from the hexagonal symmetry revealed by its powder diffraction data. The goal of this study was to obtain a complete set of atomic coordinates and the temperature factor and occupation factor for each atom in this structure by applying the Rietveld profile analysis technique to powder x-ray diffraction data. Samples of several bulk compositions in the range 0 less than or equal to x less than or equal to 4 were prepared in order to evaluate the solid solution limits of the apatite phase. The structure of Ca/sub 2/Nd/sub 8/(SiO/sub 4/)/sub 6/O/sub 2/ has been shown to be isostructural with Ca/sub 10/(PO/sub 4/)/sub 6/F/sub 2/. The metal ions occupying the 4f site are coordinated by six silicate oxygens at an average distance of 2.56 A. The Nd(+3) ions occupying the 6h site are coordinated by six silicate oxygens at an average distance of 2.49 A and by one anionic oxygen at 2.27 A. The anionic oxygen in 2a is coordinated by three Nd(+3) ions. The structure of Ca/sub 3/Nd/sub 7/(SiO/sub 4/)/sub 6/O/sub 1/ /sub 5/ is similar except that five Nd(+3) and one Ca(+2) ions occupy the 6h site and 1/4 of the anionic oxygens are missing in a random fashion.

• Research Organization: Pacific Northwest Lab., Richland, WA (USA); Bronx Community Coll., New York (USA)
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 6232358
• Report Number(s): PNL-SA-9377; CONF-810675-4; ON: DE81030079; TRN: 81-016815
• Resource Relation: Conference: 15. rare earth research conference, Rolla, MO, USA, 15 Jun 1981
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
CALCIUM SILICATES
HEXAGONAL LATTICES
STOICHIOMETRY
NEODYMIUM SILICATES
OXYGEN COMPOUNDS
APATITES
CALCINED WASTES
CERAMICS
EXPERIMENTAL DATA
LATTICE PARAMETERS
TEMPERATURE EFFECTS
X-RAY DIFFRACTION
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DATA
DIFFRACTION
INFORMATION
MATERIALS
MINERALS
NEODYMIUM COMPOUNDS
NUMERICAL DATA
RADIOACTIVE MATERIALS
RADIOACTIVE WASTES
RARE EARTH COMPOUNDS
SCATTERING
SILICATES
SILICON COMPOUNDS
WASTES
400201* - Chemical & Physicochemical Properties
052001 - Nuclear Fuels- Waste Processing