Weiming Xu

TL;DR: Following single crystal x-ray diffraction, Mössbauer and Raman spectroscopy measurements supported by ab initio calculations, the H-bonds symmetrization in iron oxyhydroxide, FeOOH, resulting from the Fe(3+) high-to-low spin crossover at above 45 GPa is reported.

TL;DR: In this article, an analysis of the electrical transport, magnetic, and structural properties with pressure increase and at the transition range suggests that the coinciding IM transition, magnetic moment, and volume collapse at around 50 GPa are caused by the closure of the Hubbard gap driven by the high-spin to low-spin (HS-LS) transition.

Abstract: Electronic/magnetic transitions and their struc- tural consequences in Fe-based Mott insulators in a re- gime of very high static density are the main issue of this short review paper. The paper focuses on the above-men- tioned topics based primarily on our previous and on- going experimental HP studies employing: (i) diamond anvil cells, (ii) synchrotron X-ray diffraction, (iii) 57 Fe Mossbauer spectroscopy, (iv) electrical resistance and (v) X-ray absorption spectroscopy. It is shown that applying pressure to such strongly correlated systems leads to a number of changes; including quenching of the orbital moment, quenching of Jahn-Teller distortion, spin cross- over, inter-valence charge transfer, insulator-metal tran- sition, moment collapse and volume collapse. These changes may occur simultaneously or sequentially over a range of pressures. Any of these may be accompanied by or be a consequence of a structural phase transition; namely, a change in crystal symmetry. Analyzing this rich variety of phenomena we show the main scenarios which such strongly correlated systems may undergo on the way to a correlation breakdown (Mott transition). To illustrate these scenarios we present recent results for MFeO3 (M ¼ Fe, Ga, Lu, Eu, Pr) and CaFe2O4 ferric oxi- des; FeCl2 and FeI2 ferrous halides, and FeCr2S4 sulfide. Fe3O4 is given as an example case for the impact of Mossbauer Spectroscopy on High Pressure Crystallogra- phy studies.

TL;DR: In this article, it was found that the crystal structure is stable at least to 82 GPa, though a significant change in compressibility has been observed above 50 GPa and the HS-LS transition is accompanied by an appreciable resistance decrease remaining a semiconductor up to 115 GPa.

TL;DR: In this paper , an unusual electronic state characterized by a "mixed" HS/LS state with a stable abundance ratio realized in the crystal structure with a single Fe site within a wide pressure range of ~ 50-106 GPa.