Absorption correction for plate samples in transmission X-ray powder diffraction: improved reliability of atomic displacement parameters

Abstract

Absorption in transmission X-ray powder diffraction introduces angle-dependent intensity distortions that can bias refined structural parameters. We present an analytical absorption correction for flat plate samples, derived from the geometry and applicable to both point and area detectors. The correction separates into a scale term and an angle-dependent component; while the former is absorbed by the refinement scale factor, the latter affects relative intensities and biases parameters such as atomic displacement parameters (ADPs). Using CeO₂, we show that neglecting absorption leads to systematic variation of ADPs with optical thickness, which is removed by applying the correction. Plate geometry further allows independent determination of the optical thickness, enabling absorption to be treated as a physically constrained correction and improving refinement reliability.