ИСТИНА

We present an extension of the well-established Rietveld refinement method for modeling two-dimensional neutron time-of-flight powder-diffraction data, i.e., intensity as function of diffraction angle 2θ and wavelength λ. For the future instrument POWTEX [1] at FRM II and also for the future powder diffractometer DREAM at the ESS, this novel approach will fully exploit the varying resolution with 2θ and λ which is otherwise lost when integrating with today’s standard refinement procedures. For a proof-of-concept, powder diffraction data of CuNCN and diamond was collected at POWGEN, SNS, Oak Ridge. Major steps of this new analysis are as follows. Using a modified reduction procedure the POWGEN event data is binned logarithmically in d and linearly in d⊥, a newly introduced variable. Together they span an alternative orthogonal variable space [2]. The 2D (dimensional) pattern is corrected for 2D-background and calibrated by a 2D-vanadium pattern to account for detector efficiency and the wavelength-dependent intensity distribution. A suitable 2D analytical profile function describing the instrument characteristics needs to be established for the data refinement. Therefore, the peak profile as a function of 2θ and λ is determined from a reference samples and provided to the user as an instrumental resolution file. Finally, we aim to implement the multi-dimensional refinement procedure into common Rietveld program suites in order to allow the users all necessary data-treatment possibilities. This new development is open for joint activities with program authors of existing user software, and we welcome current considerations towards an implementation into GSAS II. [1] H. Conrad, T. Brückel, W. Schäfer and J. Voigt; POWTEX–the high-intensity time-of-flight diffractometer at FRM II for structure analysis of polycrystalline materials; J. Appl. Crystallogr., 41, 836 (2008); DOI: 10.1107/S0021889808022905. [2] P. Jacobs, A. Houben, W. Schweika, A. L. Tchougréeff and R. Dronskowski; A Rietveld refinement method for angular- and wavelength-dispersive neutron time-of-flight powder diffraction data; J. Appl. Crystallogr., 48, 1627 (2015); DOI: 10.1107/S1600576715016520.