Crystal structure and thermal expansion of. cap alpha. -quartz SiO/sub 2/ at low temperatures
The crystal structure of ..cap alpha..-SiO/sub 2/ (low quartz) has been refined at 296, 78, and 13 K from time-of-flight neutron powder diffraction data. The major effect of temperature from 296 to 78 K is a nearly rigid body rotation of the SiO/sub 4/ tetrahedra. Below 78 K, tetrahedral rotation is substantially reduced giving rise to a much smaller thermal expansion. A comparison of the volume dependence of the Si-O-Si angle, the rotation angle for SiO/sub 4/ tetrahedra and the c/a ratio suggests that the mechanism for expansion may be changing from tetrahedral rotation to tetrahedral distortion at the lowest temperatures. The inverse linear relation between the mean Si-O bond distance and -sec(Si-O-Si) which has been observed for silica minerals at both ambient and high-temperature conditions appears to be consistent with the structural variations that occur at low temperatures.
- Research Organization:
- Department of Geology, University of Louisville, Louisville, Kentucky 40292
- OSTI ID:
- 7085850
- Journal Information:
- J. Appl. Phys.; (United States), Vol. 53:10
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
QUARTZ
CRYSTAL STRUCTURE
THERMAL EXPANSION
BOND ANGLE
BOND LENGTHS
EXPERIMENTAL DATA
LATTICE PARAMETERS
LOW TEMPERATURE
MATHEMATICAL MODELS
MEDIUM TEMPERATURE
NEUTRON DIFFRACTION
POWDERS
SPACE DEPENDENCE
TEMPERATURE EFFECTS
TETRAGONAL LATTICES
TIME-OF-FLIGHT METHOD
ULTRALOW TEMPERATURE
VERY LOW TEMPERATURE
CHALCOGENIDES
COHERENT SCATTERING
CRYSTAL LATTICES
DATA
DIFFRACTION
DIMENSIONS
EXPANSION
INFORMATION
LENGTH
MINERALS
NUMERICAL DATA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SCATTERING
SILICON COMPOUNDS
SILICON OXIDES
360603* - Materials- Properties