ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Bragg intensities of β-PbF2 (with the cubic fluorite structure) have been measured in the step-scan mode up to sin θ/λ = 1.17 Å-1 at 295, 461 and 625 K by X-ray diffraction: a = 5.925 (2), 5.952 (2), 5.982 (4) Å, respectively; R = 0.013 for 103 reflections, 0.015 for 103 reflections, 0.018 for 106 reflections, respectively. The intensities were used for the refinement of anharmonic temperature factors up to third order for F- and up to sixth order for Pb2+. The temperature-factor formalism was based on the Gram-Charlier expansion. The probability density function (p.d.f.) of the F- and Pb2+ ions were calculated from the coefficients of the anharmonic temperature factors. The p.d.f. maps gave clear evidence that the Pb2+ ions do not carry out isotropic thermal motion. The atomic potentials of the Pb2+ ions (derived from the p.d.f. maps) indicate that the thermal motion of the excited Pb2+ ions is strongly influenced by the repulsion terms along the Pb2+-F- bonds. The F- ions carry out their largest thermal vibrations along 〈111〉 towards the centre of the elementary cell.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739482001466
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