Recent developments and diffuse scattering studies at beamline F1 (Hasylab/DESY)

Abstract

In order to enhance data collection possibilities at beamline F1 a new marresearch CCD-detector with an active area of 165 mm in diameter (20482 pixels in 2x2 binning) has been installed in February 2005 to replace an older CCD-system which was in operation since 1996. To increase the quantum efficiency for energies between 20 and 30 keV the detectors are fitted with 100 μm Gd2O2S2:Tb phosphor instead of a standard 40 μm phosphor. A previously developed software suite [1] for the reconstruction of diffuse scattering from CCD raw data has been adopted to the new data format and successfully applied in a compositionand temperature-dependent study of precursor-induced diffuse scattering in V-diluted lead-phosphates. Compared to pure lead-orthophosphate, the system Pb3(PxV1-xO4)2 displays a complex sequence of phase transitions. The CCD-data show an overall rhombohedral symmetry (R-3m) of the paraelastic high-temperature phase, but broad diffuse intensities are clearly visible even 40 K above Tc. These maxima are centered around symmetry-allowed Bragg-reflections of the paraelastic HT-phase and must be indexed by half integers. The diffuse scattering shows a slight anisotropic spatial distribution in reciprocal space with an elongation along a*, indicating a higher degree of disorder along [111]rh. This effect results from small (ca. 50 A), dynamic precursor-clusters of the monoclinic ferroelastic LTphase in an overall paraelastic matrix.