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Crystallite-size distributions and diffraction line profiles near the peak maximum

Published online by Cambridge University Press:  10 January 2013

Giuseppe Allegra  and
Sergio Brückner
Giuseppe Allegra
Affiliation:
Dipartimento di Chimica, Politecnico di Milano, P.zza L.da Vinci 32, I-20133 Milano, Italy and Dipartimento di Chimica, Univ. di Modena, via G. Campi 183, I-41100 Modena, Italy
Sergio Brückner
Affiliation:
Dipartimento di Chimica, Politecnico di Milano, P.zza L.da Vinci 32, I-20133 Milano, Italy and Dipartimento di Chimica, Univ. di Modena, via G. Campi 183, I-41100 Modena, Italy
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Abstract

The effect of crystallite-size distribution on the shape of X-ray diffraction peaks from powder samples is investigated focusing the attention on the region within the top half of intensity. It is shown that, unlike profile tails, this central region can markedly depart from the Lorentzian shape for crystallite-size distributions that are quite acceptable from the physical point of view. Goal of this paper is to correlate the well-known m parameter in the Pearson VII function or the η weight in the pseudo-Voigt function with a number of different distributions of crystallite dimensions ranging from the δ function of all-equal-sized crystals to a very broad distribution. The suitably normalized curvature at the peak is a possible new parameter; its correlation with m and η is shown. Also, a procedure is suggested to derive the volume-average crystal thickness 〈Tw〉 from the FWHM and the knowledge of either m or η.

Type
Research Article
Information
Powder Diffraction , Volume 8 , Issue 2 , June 1993 , pp. 102 - 106
Copyright
Copyright © Cambridge University Press 1993

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