Ab Initio and Experimental Investigations on the Influence of Cation Ordering on the Elasticity of (Mg,Fe,Mn)Al₂O₄ Spinels

We explore the effect of cation disorder on the elastic properties of the (Mg,Fe,Mn)Al₂O₄ spinel systems using DFT and Brillouin scattering. The spinel structure (Fd-3m), [A_(1−x),B_x]^IV[A_xB_(2−x)]^VIO₄ (A=Mg,Mn,Fe; B =Al), is highly relevant in geosciences as it is adopted by some key oxide minerals in the Earth's upper mantle and transition zone, between 0-660km depth. In addition, due to the high-pressure/temperature stability of spinels, they also have industrial applications, e.g., as ceramic materials. The effect of disorder, quantified by the inversion parameter x, has been addressed for MgAl₂O₄-spinel. In our work, we extend these investigations to include the influence of magnetic cations, A =Mn or Fe. How disorder changes the physical properties in spinels is important to understand not only because it could have profound geophysical implications, as the degree of disorder is controlled by pressure, temperature, and perhaps local chemistry, but also to optimize their technological applications. Thus, within the LDA and GGA we study in a systematic way the impact of x in our spinels and compare the results to Brillouin scattering measurements to draw trends in their properties.