The Application of the Fundamental Parameters Approach as Implemented in TOPAS to Divergent Beam Powder Diffraction Data

Published

May 1, 2010

Author(s)

James P. Cline, David R. Black, David L. Gil, Albert Henins, Donald A. Windover

Abstract

The fundamental parameters approach (FPA) as implemented in TOPAS is investigated for analyses of conventional X-ray powder diffraction (XRPD) data. The FPA involves the convolution of a series of models, each one constituting an individual contribution to the geometric portion of the instrument profile function (IPF). Parameters within each model are refined in a least squares context to yield a presumably accurate description of the experiment. If one wishes to interrogate the functionality of said models, a diffractometer wherein the uncertainties in optical character are minimized is required. To this end, a diffractometer was built at NIST which featured conventional divergent beam optics in conjunction with a well aligned, stiff and accurate goniometer assembly. Initial results indicated that the detector arm was flexing; this problem has been addressed with the fabrication and installation of new arm and counterweight assembly. Data collected from NIST Standard Reference Material (SRM) 660a, lanthanum hexaboride, are analyzed using the FPA method to yield conclusions on the validity of the models with respect to shape and position of the diffraction profiles.

Citation

Materials Science Forum

Pub Type

Others

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Keywords

Powder Diffraction, Fundamental Parameters Approach, Profile Fitting, Rietveld Analysis, Standard Reference Materials, Lattice Parameter Measurement

Citation

Cline, J. , Black, D. , Gil, D. , Henins, A. and Windover, D. (2010), The Application of the Fundamental Parameters Approach as Implemented in TOPAS to Divergent Beam Powder Diffraction Data, Materials Science Forum, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=905010 (Accessed October 8, 2025)