npj: 超高压之下的Fe2O3—在地球内部的性质和演化
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含铁氧化物作为研究Mott转变的模型对象,在地球下地幔和外核的矿物学中起着重要作用。最近,由于它们在高压-高温条件下具有复杂的电子、磁性和晶体结构行为,这些化合物引起了人们极大的兴趣。
The archetypal 3d Mott insulator hematite, Fe2O3, is one of the basic oxide components playing an important role in mineralogy of Earth’s lower mantle. Its high pressure–temperature behavior, such as the electronic properties, equation of state, and phase stability is of fundamental importance for understanding the properties and evolution of the Earth’s interior. Here, we study the electronic structure, magnetic state, and lattice stability of Fe2O3 at ultra-high pressures using the density functional plus dynamical mean-field theory (DFT + DMFT) approach. In the vicinity of a Mott transition, Fe2O3 is found to exhibit a series of complex electronic, magnetic, and structural transformations. In particular, it makes a phase transition to a metal with a post-perovskite crystal structure and site-selective local moments upon compression above 75 GPa. We show that the site-selective phase transition is accompanied by a charge disproportionation of Fe ions, with Fe3±δand δ ~ 0.05–0.09, implying a complex interplay between electronic correlations and the lattice. Our results suggest that site-selective local moments in Fe2O3 persist up to ultra-high pressures of ~200–250 GPa, i.e., sufficiently above the core–mantle boundary. The latter can have important consequences for understanding of the velocity and density anomalies in the Earth’s lower mantle.
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