AUTOMATED RIETVELD-ANALYSIS OF LARGE NUMBERS OF DATASETS, S. Vogel, H.-G. Priesmeyer, pp. 91-95

During investigations of phase transformation kinetics by diffraction techniques, several hundreds or even thousands of diffraction patterns are collected. Automation of the data analysis process is mandatory to perform for example a long sequence of Rietveld refinements. The Bragg edge transmission (BET) technique, a neutron time-of-flight method, allows acquiring patterns of sufficient statistics to derive structural information on the sample within the order of 10 seconds. For data analysis of such BET patterns a Rietveld-type of software was developed. To allow efficient analysis of a large number of patterns collected during investigations of phase transitions by BET, the automation presented here was included in this software. It is based on a script language capable of loops and conditional fitting. A single result file containing the desired variables (volume fractions, lattice parameters etc.) is created. An application example and possible consistency checks for the results are also presented. Although the concepts were developed for BET data, they should be widely transferable to powder diffraction data analysis. Introduction The available intensities at modern synchrotron and neutron sources allow time-resolved diffraction [1]. Applications of time-resolved diffraction include investigations of kinetics of phase transformations and chemical reactions (e.g. [2]). During the course of such an experiment, hundreds or even thousands of datasets are created. The number of spectra to be analysed will still further increase, once BET imaging becomes possible. Manual analysis using the Rietveld method [3] of such huge numbers of datasets is impractical. Hence, an automation of the Rietveld procedure is required. Such automation is also convenient in the case of analysis of small numbers of similar patterns, e.g. a sample under different loads in a stress/strain measurement. A novel neutron technique, so-called Bragg-edge transmission (BET), allows time-resolved studies at pulsed neutron sources with time resolutions in the order of 10 seconds. For this technique, the neutron intensity transmitted through the sample rather than the intensity diffracted by the sample is used. As this intensity is much higher than the intensity typically detected in a diffraction setup, the temporal resolution is much better than in the case of a diffraction experiment. The crystallographic information is obtained from the so-called Braggedges that appear in the transmitted spectrum [4]. A Rietveld-type of software for the dataanalysis of such spectra named BETMAn (Bragg-Edge Transmission Measurement Analysis software) was developed [5]. Although the automation procedure described here so far works on Bragg-edge transmission data, the general principles and conclusions presented are transferable Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol.44 91