The effect of data quality and model parameters on the quantitative phase analysis of X-ray diffraction data by the Rietveld method

Abstract

The quality of X-ray powder diffraction data and the number and type of refinable parameters have been examined with respect to their effect on quantitative phase analysis (QPA) by the Rietveld method using data collected from two samples from the QPA round robin [Madsen, Scarlett, Cranswick & Lwin (2001). J. Appl. Cryst. 34, 409–426]. From the analyses of these best-case-scenario specimens, a series of recommendations for minimum standards of data collection and analysis are proposed. It is hoped that these will aid new QPA-by-Rietveld users in their analyses.

In-situ laboratory X-ray diffraction applied to assess cement hydration

“…Step sizes within 0.011-0.024° 2θ are generally used, which provide adequate resolution and agree with the values proposed by Rowles [100]. Finally, using a knife-edge (or beam knife) is also an interesting choice.…”

“…Thus, the set chosen must allow the equipment to apply enough radiation to provide reasonable intensity counts within the short period of in-situ analysis. In this regard, Rowles [100] recently investigated the effect of data quality and model parameters on Rietveld QPA results, concluding that a maximum intensity of at least 5000 counts above background is desired in powder XRD for samples that contain minor/trace phases. This is close to that usually observed for in-situ XRD measurements in cementitious samples, with maximum intensities reaching around 3000-5000 counts [24,37,72,101].…”

Enhancing Bone Implants: Magnesium-Doped Hydroxyapatite for Stronger, Bioactive, and Biocompatible Applications

“…value is well below the threshold of 4.0%. 45 The unit cell parameters obtained from the Rietveld refinement of the samples, as shown in Table 1, confirm the formation of the apatite structure. The results demonstrate that the c/a parameter decreases as the Mg 2+ /PO 4 3− ratio increases, indicating an increase in the dimension of the a axis and a decrease in the dimension of the c axis.…”

A method for pole figure measurements via a dynamic segmented spiral scheme

“…As noted in several quantitative phase analysis round robins involving Rietveld refinement that do not add the additional complexity of texture effects (powdered materials), significant deviations can occur due to choices made by the operator (Madsen et al, 2001;Fawcett et al, 2010). The large number of variables (Fawcett et al, 2010), the dependence of accuracy on converged parameters across all data sets (Vogel et al, 2018), the complex procedure (Wenk et al, 2010) and the effect of order of refinement (Rowles, 2021) have each been identified as contributing factors in these deviations. One advantage of complete and even pole figure measurement techniques to determine phase fraction is that the bias errors due to texture are accounted for without requiring Rietveld refinement.…”