Use of R Factors in the Study of the Structural Defects in Phyllosilicates by X-ray Powder Diffraction

The R factors employed in crystal structure analysis can also be used in connection with clay minerals to determine the amount of defects whose types are already known. For this purpose, using the unit‐cell parameters of kaolinite with identical layers, (02,11) and (20,13) diffraction bands were calculated on the basis of a variable parameter model containing only ±b/3 translational stacking faults. The parameters of the model were varied to obtain the best fit between the calculated and observed patterns with respect to both intensity and profile. Three different R factors were used as a criterion for the best fit and the parameters yielding the smallest R value were accepted as describing the actual structure. In addition, a linear regression analysis is performed between observed and calculated intensities to determine the quality of the fit. Correlation coefficients, obtained from this analysis, are used as an indication of the effectiveness of corresponding R factors.