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Analytical models for isotropic random surface fractals with tunable fractal dimension, d/; and variable microstructural parameters are used to investigate the microabsorption of X-rays scattered symmetrically from planar samples. The models characterize homogeneous materials the constituents of which differ by their linear absorption coefficients. The absorption contrast between the fractal scattering phase and the mean value of the material is assumed to be small. It is shown that the microabsorption is maximum if the fractality of the internal surface is low (df ~ 2) whereas it vanishes for df ~ 3 irrespective of other microstructural parameters and the absorption contrast. For one of the models, a simple analytical expression is presented describing the microabsorption effect of surface fractals with an accuracy of about 20% for arbitrary fractal dimension and volume fraction.

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A correction technique for powder diffraction data recorded in transmission geometry is proposed. It considers the influence of sample inhomogeneities on the absorption of the scattered X-rays. The correction procedure is given for three typical types of samples: (i) homogeneous samples with constant thickness and small absorption contrast, (ii) samples with locally fluctuating sample thickness, and (iii) samples with non-negligible absorption contrast. The given expressions were tested by applying them to Rietveld analysis of powder diffraction data of YBa2Cu307_6 specimens.

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