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short communications
If the crystallites making up a diffractometer specimen have a number-average size 〈p〉, and the distribution function of crystallite sizes has a variance Wp and skewness γp, the crystallite size obtained from the slope of the variance-range curve will be
and that obtained from the intercept will be
Even when Wp and γp are unknown these equations set an upper limit of p22/p1 to 〈p〉; for Langford's submicron nickel this limit is 121 Å.