Revista mexicana de física
versão impressa ISSN 0035-001X
FUENTES-MONTERO, L; TORRES, E; MONTERO, M.E e FUENTES, L. A simplified rietveld code for quantitative phase analysis: development, test and application to uranium mineral So. Rev. mex. fis. [online]. 2007, vol.53, suppl.3, pp. 108-112. ISSN 0035-001X.
As part of a team project about geological sampling in the environment of the city of Chihuahua, x-ray diffraction (XRD) phase analysis of different rock types is required. The most accepted technique to perform quantitative XRD phase analysis is the well-known Rietveld method. Rietveld codes (Fullprof, Rietan, Rietica, DBWS, Topas,...), oriented to a complete characterization of the diffraction pattern (from crystal structure to texture and crystal size investigation) have been developed by several authors. The majority of these codes show a high level of automation, but application may be long and troublesome anyway. False minima and instabilities during software running are recognized problems and represent current working lines of specialized groups. As the samples considered in the present geological investigation are particularly difficult for the Rietveld technique, it was decided to develop a program that performs phase analysis by an alternative route, with a degree of automation between Rietveld and the so-called Direct Comparison Method. The Basic Rietveld-ENhanced Diffraction Analysis (BRENDA) code has been developed and tested. BRENDA uses structure-factor (and other theoretical parameters) calculations from well-established diffraction codes (Fullprof, PowderCell), refines experimental diffraction peaks' profiles and intensities by means of a robust algorithm and determines phases' concentrations. Application of BRENDA code to computer-simulated problems, NIST standards and geological samples is divulged. Discrepancies with calibration figures are of the order of declared uncertainties. The advantages and disadvantages of the considered diffraction methods are discussed. In practice, being only half-automated gives the user more control of the refinement process and leads to an overall economy of time and higher reliability.
Palavras-chave : Quantitative phase analysis; Rietveld; uranium minerals.