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CrO2 can undergo the pressure-induced phase transition sequence of rutile-type → CaCl2-type → pyrite-type → Pnma → (Fe2P-type→) I4/mmm.

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Greigite (Fe3S4), isostructural with Fe3O4 has recently attracted great scientific interests from material science to geology due to its complicated structure and electronic and magnetic configurations. Here, an investigation into the structural, magnetic and electronic properties of Fe3S4 under high pressure has been conducted by first-principle calculations based on density functional theory. The results show that a first-order phase transition of Fe3S4 would occur from the inverse spinel (SP) structure to the Cr3S4-type (CS) structure at 3.4 GPa, accompanied by a collapse of 9.7% in the volume, a redistribution of iron cations, and a half-metal to metal transition. In the CS-Fe3S4, Fe2+ located at octahedral environment firstly undergoes a transition from high-spin (HS) state to low-spin (LS) state at 8.5 GPa and Fe3+ subsequently does at 17 GPa. The Equation of State for different phases of Fe3S4 are also determined. Our results not only give some clues to explore novel materials by utilizing Fe3S4 but also shed light on the fundamental information of Fe3O4, as well as those of other SP-AB2X4 compounds.

Oxygen is thought to be an important light element in Earth’s core but the amount of oxygen in Earth’s core remains elusive. In addition, iron-rich iron oxides are of great interest and significance in the field of geoscience and condensed matter physics. Here, static calculations based on density functional theory demonstrate that I4/mmm-Fe2O is dynamically and mechanically stable and becomes energetically favorable with respect to the assemblage of hcp-Fe and -FeO above 270 GPa, which indicates that I4/mmm-Fe2O can be a strong candidate phase for stable iron-rich iron oxides at high pressure, perhaps even at high temperature. The elasticity and anisotropy of I4/mmm-(FexNi1−x)2O at high pressures are also determined. Based on these results, we have derived the upper limit of oxygen to be 4.3 wt% in Earth’s lower outer core. On the other hand, I4/mmm-(FexNi1−x)2O with high AV S is likely to exist in a super-Earth’s or an ocean planet’s solid core causing the locally seismic heterogeneity. Our results not only give some clues to explore and synthesize novel iron-rich iron oxides but also shed light on the fundamental information of oxygen in the planetary core.

Iron oxides play an important role in planetary evolution, but little information about the structural properties of AX2‐type iron oxides under extreme conditions limits our understanding of the so‐called “super‐Earth” planets. Here an investigation into the high‐pressure behavior of FeO2 as well as its sulfide counterpart FeS2, has been conducted by first‐principle calculations based on density functional theory. Both FeO2 and FeS2 are predicted to undergo a italicPatrue3¯‐ Rtrue3¯m‐I4/mmm transition sequence at extreme pressure. Differences in high‐pressure behaviors between FeO2 and FeS2 have been discussed in detail, such as effective coordination number and elasticity. This study not only resolves the controversy about the structural stability of FeS2 under high pressure but also suggests the tenfold coordinated I4/mmm‐type FeO2 may contribute to local chemical heterogeneity by accumulation in the deep interior of a large super‐Earth or water‐rich planet, whose pressure at the core‐mantle boundary can reach 2 TPa.

Cs 2 SnI 6-x Br x (x = 0-6) solid solutions have been synthesized by chemical solid solution reaction in conjunction with sintering under vacuum. The Rietveld refinements of powder Xray diffraction (XRD) patterns indicate that all the samples are cubic, with a symmetry of Fm3m. The lattice parameter a decreases linearly as a function of the Br content in Cs 2 SnI 6-x Br x . Raman spectra suggest that the new Raman peaks might derive from the short-range ordering of I/Br anions. The UV/Vis reflec- [a]

Nitrogen (N) is one of the most significant volatiles in our planet, an essential element for life, and the primary component of the atmosphere. Nitrogen in the Earth's interior is linked to that near the surface through processes of subduction and volcanic outgassing, influencing the partial pressure (P) of atmospheric N in a profound way (Busigny et al., 2019;Mikhail & Sverjensky, 2014). This "deep nitrogen" also provides crucial insights into planetary evolution, including the accretion and differentiation of the core and mantle