ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Accurate integrated intensities for the Bragg reflexion of neutrons from two single crystals of SrF2 have been measured at temperatures between 295 and 1043 °K. Corrections for extinction and thermal diffuse scattering were applied and the experimental data were analysed in terms of a model which includes both harmonic and anharmonic components in the thermal vibrations of the atoms. Significant contributions from the third-order anharmonic term, βF, in the one-particle potential of the fluorine atoms, consistent with their tetrahedral site symmetry, were observed at all temperatures. At 773 °K significant anisotropic fourth-order components, δSr and δF, became apparent in the thermal vibration of both the strontium and the fluorine atoms. At this temperature βF was refined to - 3.45 ( ± 0.11) × 10-12 erg Å-3, with δSr = 1.30 ( ± 0.75) × 10-12 erg Å-4 and δF = 0.84 (± 0.29) × 10-12 erg Å-4. The positive signs of the parameters δSr and δF result from the influence of Coulombic forces on the atomic vibrations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739474001902
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