High‐quality single‐crystals of (Al,Fe)‐bearing bridgmanite, Mg_0.88 Fe³⁺_0.065Fe²⁺_0.035Al_0.14Si_0.90O₃, of hundreds of micrometer size were synthesized at 24 GPa and 1800 °C in a Kawai‐type apparatus from the starting hydrous melt containing ~6.7 wt% water. Analyses of synthesized bridgmanite using petrographic microscopy, scanning electron microscopy, and transmission electron microscopy show that the crystals are chemically homogeneous and inclusion free in micrometer‐ to nanometer‐spatial resolutions. Nanosecondary ion mass spectrometry (NanoSIMS) analyses on selected platelets show ~1,020(±70) ppm wt water (hydrogen). The high water concentration in the structure of bridgmanite was further confirmed using polarized and unpolarized Fourier‐transform infrared spectroscopy (FTIR) analyses with two pronounced OH‐stretching bands at ~3,230 and ~3,460 cm⁻¹. Our results indicate that lower‐mantle bridgmanite can accommodate relatively high amount of water. Therefore, dehydration melting at the topmost lower mantle by downward flow of transition zone materials would require water content exceeding ~0.1 wt%.

We measured the effect of pressure on the compressional and shear wave velocity (V_P, V_S) as well as density of Fe‐bearing bridgmanite, Mg_0.96(1)Fe²⁺_0.036(5)Fe³⁺_0.014(5)Si_0.99(1)O₃, using impulsive stimulated light scattering, Brillouin light scattering, and X‐ray diffraction, respectively, in diamond anvil cells up to 70 GPa at 300 K. A drastic softening of V_P by ~6(±1)% is observed between 42.6 and 58 GPa, while V_S increases continuously with increasing pressure. A significant reduction in Poisson's ratio from 0.24 to 0.16 occurs at ~42.6–58 GPa, while V_S increases by ~3(±1)% above ~40 GPa compared to MgSiO₃‐bridgmanite. Thermoelastic modeling of the experimental results shows that the observed elastic anomaly of Fe‐bearing bridgmanite is consistent with a spin transition of octahedrally coordinated Fe³⁺ in bridgmanite. These results challenge traditional views that Fe enrichment will reduce seismic velocities, suggesting that seismic heterogeneities in the mid‐lower mantle may be due to a spin transition of Fe in Fe‐bearing bridgmanite.

Periodic structures of GdN particles encapsulated in a single crystalline GaN matrix were prepared by plasma assisted molecular beam epitaxy. High resolution x-ray diffractometery shows that GdN islands, with rock salt structure are epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron microscopy combined with in situ reflection high energy electron diffraction allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one due to GdN particles with Curie temperature of 70 K and a second, anomalous above room temperature phase.

Understanding the effect of carbon on the density of hcp (hexagonal-close-packed) Fe-C alloys is essential for modeling the carbon content in the Earth’s inner core. Previous studies have focused on the equations of state of iron carbides that may not be applicable to the solid inner core that may incorporate carbon as dissolved carbon in metallic iron. Carbon substitution in hcp-Fe and its effect on the density have never been experimentally studied. We investigated the compression behavior of Fe-C alloys with 0.31 and 1.37 wt % carbon, along with pure iron as a reference, by in-situ X-ray diffraction measurements up to 135 GPa for pure Fe, and 87 GPa for Fe-0.31C and 109 GPa for Fe-1.37C. The results show that the incorporation of carbon in hcp-Fe leads to the expansion of the lattice, contrary to the known effect in body-centered cubic (bcc)-Fe, suggesting a change in the substitution mechanism or local environment. The data on axial compressibility suggest that increasing carbon content could enhance seismic anisotropy in the Earth’s inner core. The new thermoelastic parameters allow us to develop a thermoelastic model to estimate the carbon content in the inner core when carbon is incorporated as dissolved carbon hcp-Fe. The required carbon contents to explain the density deficit of Earth’s inner core are 1.30 and 0.43 wt % at inner core boundary temperatures of 5000 K and 7000 K, respectively.