Cation Disorder of Mg2SiO4 in Super‐Earth Mantles

Abstract Understanding the mineralogy of exoplanets is essential for unraveling their interior structures, dynamics, and evolution. For large super‐Earths, the post‐post spinel , one of the major mantle phases, may undergo the order‐disorder transition (ODT) at high temperatures. However, the ODT phase boundary of has not been rigorously constrained. Additionally, fundamental thermodynamic properties of the disordered remain poorly investigated. Here, we develop a unified machine learning potential (MLP) for of ab initio accuracy under super‐Earth mantle conditions. With the efficient MLP, we extensively calculate the free energy of post‐post spinel via the thermodynamic integration method. The results are used to constrain the ODT phase boundary. Furthermore, we report the P‐V‐T equation of state and Grüneisen parameters for post‐post spinel across various degrees of disorder. These thermodynamic properties are further applied to update the adiabatic thermal profiles and the mass‐radius relation of super‐Earths.