A first-principles study of the structural, electronic and elastic properties of the FeO₂–FeO₂He system under high pressure

Abstract

The origin of the wave velocity anomalies at the core-mantle boundary (CMB) has been controversial. The primordial helium reservoir in the deep lower mantle remain elusive even with geochemical evidence...

Ultra‐Low Velocity Zones Beneath the Southern Hemisphere Imaged With Double‐Array Stacking of PcP Waveforms

“…Our study region is located within a presumed cooler portion of the lowermost mantle, away from the LLVPs (Figure 10); therefore, a compositional origin may better explain our robust ULVZ observations, as opposed to a thermal‐only origin. As mentioned in Section 1, compositionally distinct ULVZs may result from iron‐enrichment above the CMB, which could be caused by chemical reactions between the silicate mantle and the iron outer core (Kim et al., 2020; Knittle & Jeanloz, 1989; Liu et al., 2023; Ma et al., 2019; Mao et al., 2005, 2006; Nomura et al., 2011; Otsuka & Karato, 2012; Tanaka et al., 2020). That said, the production rate of deep mantle iron‐enrichment processes is unclear, and it is uncertain whether such processes would generate sufficient ULVZ materials to explain the widespread distribution observed in our results.…”

“…Such anomalies could, for instance, be generated by iron-enrichment (Kim et al, 2020;Knittle & Jeanloz, 1989;Lai et al, 2022;Z. Li et al, 2022;Liu et al, 2023;Mao et al, 2005Mao et al, , 2006Nomura et al, 2011;Tanaka et al, 2020) or subducted materials above the CMB (Andrault et al, 2014;Dobson & Brodholt, 2005;Hansen et al, 2023;Li et al, 2017;Su et al, 2024;Wolf et al, 2024). Alternatively, fractional crystallization of a basal magma ocean (BMO), a remnant associated with an ancient compositional reservoir at the base of the mantle, has been suggested as the source of ULVZs (Boukare et al, 2015;Labrosse et al, 2007).…”

Synthesis and Properties of the Helium Clathrate and Defect Perovskite [He2–x□x][CaNb]F6

“…For example, α decay in nuclear fuel results in the formation of helium that can, in principle, lead to bubble formation, fuel element swelling, and possibly failure. Consequently, there have been studies of the solubility and energetics of helium incorporation in materials such as actinide dioxides, and also its diffusion through the materials. − There has also been interest in the formation of helium compounds with iron, and iron oxide, in the context of exoplanet interiors and deep earth minerals, − as these materials could be important in accounting for helium abundance in the earth and solar system. The boundaries of helium chemistry have been further expanded by preparing the electride Na 2 He at >113 GPa .…”