Aluminum oxy(hydroxides) are an important class of metal oxide relevant to a wide range of industrial and environmental applications. Boehmite, AlOOH, is naturally occurring mineral precursor in the Bayer process for aluminum production, a widely used heavy metal absorbent in environmental remediation, and is the dominant aluminum phase found in the nuclear tank waste at the Hanford site. Fe(III) and Cr(III) are metal impurities common in each of these areas, and in this study we examine the properties of boehmite as a function of increasing concentration of these substituting metals. First principles calculations are used to determine and compare the electronic, vibrational, magnetic, and configurational contributions to the free energies for a series of substitutional compositions. The goal of this research is to determine the relative energetic favorability of these phase compositions to better characterize the boehmite solid state structure in the presence of these impurities. Crystal properties were calculated using DFT formalism using a plane wave basis, PAW potentials, and the GGA-PBE functional. The cluster expansion (CE) method was employed to determine effective cluster interactions (ECIs) of the metal ions. These are used to predict zero temperature, zero pressure ground state configurations for a series of compositions, whose energetics are calculated by ab initio methods. Free energies at 300K for these compositions is determined using the ECIs to perform Monte Carlo simulations using the semi-grand canonical ensemble.

First-principles study of phase stabilities in Al1-xFexOOH and Al1-xCrxOOH metal oxyhydroxides

2019 Fall National Meeting

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