Synchrotron radiation diffraction in a single crystal of paratellurite investigated with a new experimental scheme

First results are presented for synchrotron radiation diffraction in a paratellurite (TeO₂) single crystal investigated with a new experimental scheme consisting of a standard monochromator and a relatively narrow slit for collimation and monochromatization of an incident beam. The Bragg case reflection geometry is used. The monochromator, a pair of Si crystals, maintains the initial direction of the beam propagation. The theory is developed for a precise description of the instrumental function in such a scheme. A new rocking curve registration technique with use of an adaptive bending piezoactuator is applied for the first time with the aim to record the narrow diffraction peaks with high accuracy. A sample is attached to one edge of the bidomain lithium niobate single crystal piezoactuator used. The piezoactuator is bent under the influence of an electric field and it changes the angular position of the sample with a very small step. The experimental curves are compared with the calculated diffraction rocking curves of a perfect paratellurite crystal, both the theoretical one and the one calculated taking into account the instrumental function. An instrumental function account allows a complete coincidence of the simulated curves with the experimental results to be obtained if the experimental curve does not coincide with the theoretical rocking curve. A small discrepancy between the theory and the experimental data has been discovered in cases where the incident beam is sufficiently collimated and monochromated. This indicates the presence of a certain number of lattice defects in the sample under study.