ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
From bulk thermodynamic data a precise value is derived for the Debye equivalent temperature for the Debye-Waller effect: ΘM(293) = 804.5 ± 4 K. This agrees with the temperature dependence of X-ray Bragg intensities measured by Baldwin & Tompson [J. Chem. Phys. (1964), 41, 1420-1426], but rules out many pairs of values for B(Mg) and B(O) obtained from angular dependence of X-ray Bragg intensities. Only the results of Lawrence [Acta Cryst. (1973), A29, 94-95] are fully consistent. These give B(O) slightly larger than B(Mg), in agreement with shell-model calculations. Combining the thermodynamic error limits with Lawrence's gives at 293 K B(Mg) = 0.296 ± 0.009 Å2, B(O) = 0.330 ± 0.012 Å2. This gives for even-index neutron peaks Beff = 0.314 ± 0.010 Å2, compared with a recent powder measurement of Beff = 0.354 ± 0.008 Å2 which is incompatible with the thermodynamic data [unless B(O)/B(Mg) ∼ 3]. The discrepancy, though small, cannot be due to particle-size effects.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739477001521
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