Exploiting Powder X-ray Diffraction techniques for automated phase isolation in the laboratory.

10^th February 2023, 14:00
Danny Ritchie
MIF

Abstract

A chemical composition consisting of n elements can be represented as Euclidean, where the components give the relative amount of each element. Consider an experimentally prepared composition s that has been heated such that it reaches thermodynamic equilibrium. At equilibrium it will decompose into a set of phases {p}. A ubiquitous method for the identification of new phases is to trial an arbitrary s in the hope that a p is formed which is new. The problem that this work aims to address is how to find the composition of the new p. The {p} are separated into the new phase, denoted u, and the known phases, denoted {k}. Powder X-Ray Diffraction (PXRD) is an experimental technique that can be used to estimate the relative ratios of {k}, and so the average composition of the {k} can be calculated; K. The importance of this is that s will be a weighted average of u and K, and so u will lie on the line segment extending from s away from K. Unfortunately the estimation of the relative ratios from PXRD is not exact, and so rather than being a point, K must be represented as a random variable. Assuming the distribution of K to be Gaussian, the induced probability density for u is estimated by a projection of K through s.