Abstract
Two methods for an automatic analysis of the temporal evolution of a multiphase polycrystalline sample are described: The Upeak method, analyzing the spectra formally, i.e., carrying the peak search in them, and so describing the evolution in terms of spectral peaks, or having made additionally the autoindexing of the found peaks, preparing the crystallographic information for the Rietveld analysis. The Rietveld method, using an already available crystallographic information about the phase reflections, and describing the unit cell and atomic characteristics of each phase, and the mutual phase contributions to the total intensity for each item of the analyzed sequence of neutron scattering spectra.The paper describes difficulties of an automatic analysis securing the convergence of a non-linear and at the same time non-stationary fitting.The evolution of the polycrystalline compound CuFe2 O4 with the temperature T in the range from 300 to 500 degrees Celsius illustrates the performance of the methods.
Highlights
The paper describes difficulties of an automatic analysis securing the convergence of a non-linear and at the same time non-stationary fitting
In real-time experiments a multi-phase polycrystalline sample is step-wise exposed to external impacts
A sequence of neutron-diffraction spectra from this sample is measured and, analyzed in an automatic mode, displays a picture of the crystallographic phase evolution of this sample in terms of the external influences. This involves the analysis of the temporal evolution of a non-stationary regression, strongly nonlinear with respect to parameters and independent variables and, besides, containing intuitively clear but, strictly speaking, informal elements
Summary
In real-time experiments a multi-phase polycrystalline sample is step-wise exposed to external impacts (heat, mechanical ones, etc.). A sequence of neutron-diffraction spectra from this sample is measured and, analyzed in an automatic mode, displays a picture of the crystallographic phase evolution of this sample in terms of the external influences. This involves the analysis of the temporal evolution of a non-stationary regression, strongly nonlinear with respect to parameters and independent variables and, besides, containing intuitively clear but, strictly speaking, informal elements. This paper is a description of the mathematical part of these experiments (DELPHI program SPEVA).
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