ISSN:
1600-5767
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Geosciences
,
Physics
Notes:
A method is described to search for the most probable assignment of indices to powder diffractograms starting from approximate unit-cell parameters. The difference ΔQi = ΔQoi−ΔQci between observed and calculated quadratic forms of the ith peak is attributed to three contributions: ΔQi* due to imprecise unit-cell constants, ΔQi′ due to incorrect indexing and εi due to experimental error. The points ΔQi plotted as a function of ΔQoi give rise to distributions D′, D* (or under special conditions Dg*) and Dε. The differences between these distributions are evinced by differences in their moments and probability function. At the start the nearly normal distribution Dg* is searched for, by changing the initial reciprocal-cell parameters by small increments δa*, δb*, δc*. Highly probable indices can then be assigned to the Qoi's and the unit-cell constants refined by the least-squares method. At the end the normal distribution Dε with mean μ = 0 must be obtained. Statistically significant deviations of Dε from the normal distribution with μ = 0 indicate that some systematic experimental errors affect the data. The method is suitable for applications to electronic computers and is particularly recommended for plotters.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0021889870006118
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