Understanding hydrogen dissolution mechanisms in bridgmanite (Bgm), the most abundant mineral in the lower mantle, is essential for understanding water storage and rheological and transport properties in the region. However, interpretations of O-H bands in Fourier transform infrared spectroscopy (FTIR) spectra of Bgm crystals remain uncertain. We conducted density functional theory (DFT) calculations on vibrational characteristics of O-H dipoles and performed polarized FTIR measurements to address this issue. DFT calculations for four substitution models-Mg vacancies, Si vacancies, Al3+ + H+ substitution for Si4+, and Al substitution with Mg vacancies-reveal distinct O-H bands with different polarizations. Deconvolution of polarized FTIR spectra on Mg0.88Fe2+0.035Fe3+0.065Al0.14Si0.90O3 and Mg0.95Fe2+0.033Fe3+0.027Al0.04Si0.96O3 crystals shows five major O-H bands with distinct polarizations along principal crystallographic axes. These experimental and calculated results attribute O-H bands centered at 3,463-3,480, 2,913-2,924, and 2,452-2,470 cm-1 to Mg vacancies, Si vacancies, and Al3+ + H+ substitution for Si4+, respectively. The total absorbance coefficient of bridgmanite was calculated to be 82,702(6,217) L/mol/cm2. Mg and Si vacancies account for 43%-74% of the total water content, making them dominant hydrogen dissolution mechanisms in Bgm. The band frequencies for the Mg and Si vacancies in Bgm are drastically different from those in olivine and ringwoodite, corresponding to the significant changes in O-H bond strengths and in the Si and Mg coordination environments from upper-mantle to lower-mantle minerals. These results highlight the need to incorporate hydrogen dissolution mechanisms in Bgm for understanding electrical conductivity and rheology of the lower mantle.

Hydrous aluminosilicates are important deep water-carriers in sediments subducting into the deep mantle. To date, it remains enigmatic how hydrous aluminosilicates withstand extremely high temperatures in the mantle transition zone. Here we systematically investigate the crystal structures and chemical compositions of typical hydrous aluminosilicates using single-crystal X-ray diffraction, electron probe microanalyzer, and nanoscale secondary ion mass spectrometry. These single crystals are synthesized at 15.5–22.0 GPa and 1400–1700 °C, featuring pervasive structural disorders. In particular, Al and Si atoms extensively occupy new tetrahedral and octahedral sites that are nominally vacant in their ordered counterparts. High temperature activates disorders leading to variable local crystal structures and more hydrogen incorporation into the crystal structure. This result suggests that the order-to-disorder transition holds the key to the high thermal stability of hydrous aluminosilicates, significantly affecting the water cycle in the deep mantle. Activated disorder in the structure of hydrous aluminosilicates improves their thermal stability and allows more hydrogen to be incorporated into the crystal structure, impacting the deep water cycle into the lower mantle.

Equation of state (EoS) parameters of hexagonal close-packed iron (hcp-Fe), the dominant core component in large terrestrial planets, is crucial for studying interior structures of super-Earths. However, EoS parameters at interior conditions of super-Earths remain poorly constrained, and extrapolating from Earth’s core conditions introduces significant uncertainties at TPa pressures. Here, we compiled experimental static and dynamic compression data and theoretical data up to 1374 GPa and 12,000 K from the literature to refine the EoS of hcp-Fe. Using the third-order Birch–Murnaghan and Mie–Grüneisen–Debye equations, we obtained V0 (unit-cell volume) = 6.756 (10) cm3/mol, KT0 (isothermal bulk modulus) = 174.7 (17) GPa, KT0′ (pressure derivative of KT0) = 4.790 (14), θ0 (Debye temperature) = 1209 (73) K, γ0 (Grüneisen parameters) = 2.86 (10), and q (volume-independent constant) = 0.84 (5) at ambient conditions. These parameters were then incorporated into an interior model of CoRoT-7b and Kepler-10b, which includes four solid compositional layers (forsterite, MgSiO3 perovskite, post-perovskite, and hcp-Fe). The model yields the core mass fractions (CMF) of 0.1709 in CoRoT-7b and 0.2216 in Kepler-10b, suggesting a Mars-like interior structure. Extrapolation uncertainties (±10–20% in density) can change CMF by −12.6 to 21.2%, highlighting the necessity of precise EoS constraints at the super-Earth interior conditions.

Carbon materials display intriguing physical properties, including superconductivity and highly anisotropic thermal conductivity found in graphene. Compressive strain can induce structural and bonding transitions in carbon materials and create new carbon phases, but their interplay with thermal conductivity remains largely unexplored. We investigated the in situ high-pressure thermal conductivity of compressed graphitic phases using picosecond transient thermoreflectance and first-principles calculations. Our results show an anomalous thermal conductivity that peaks to 260  W/mK at 15-20 GPa but drops to 3.0  W/mK at ∼35  GPa. Together with complimentary in situ Raman and x-ray diffraction results, the abnormal thermal conductivity trend of compressed carbon is attributed to phonon-mediated conductivity influenced by interlayer buckling and sp^{2} to sp^{3} transition and, subsequently, the formation of M-carbon nanocrystals and amorphous carbon. Strain-induced structural and bonding variations provide a wide-range manipulation of thermal and mechanical properties in carbon materials.

APtO3 (A = Ca, Sr, Ba) is a unique family in the complex transition metal oxides with the AMO(3) formula. Most 3d and 4d AMO(3) compounds adopt the perovskite structure when synthesized at ambient or high pressure; however, APtO(3) perovskites have not been reported, even if their geometric tolerance factor, t, falls in the range suitable for the perovskite structure. Herein, we studied the crystal structures of BaPtO3 by performing the in situ x-ray diffraction over a broad range in the pressure (P)-temperature (T ) phase diagram. The perovskite BaPtO3 can be stabilized at P > 35 GPa and T > 1100 K. A variety of crystal structures, including the perovskite structure and its hexagonal polytypes, observed in the P-T phase diagram of BaPtO3 match the structure predictions from the first-principles calculations reasonably well.

Here we have performed single-crystal X-ray diffraction (SCXRD) experiments on two high-quality crystal platelets of (Al,Fe)-bearing bridgmanite (Mg0.88Fe0.0653+Fe0.0352+Al0.03)(Al0.11Si0.90)O-3 (Fe10-Al14-Bgm) up to 64.6(6) GPa at room temperature in a Boehler-Almax type diamond-anvil cell. Refinements on the collected SCXRD patterns reveal reliable structural information of single-crystal Fe10-Al14-Bgm, including unit-cell parameters, atomic coordinates, and anisotropic displacement parameters. Together with Mossbauer and electron microprobe analyses, our best single-crystal refinement model indicates that the sample contains similar to 6.5 mol% Fe3+, 3.5 mol% Fe2+, and 3 mol% Al3+ in the large pseudo-dodecahedral site (A site), and similar to 11 mol% Al3+ in the small octahedral site (B site). This may indicate that Al3+ in bridgmanite preferentially occupies the B site. Our results show that the compression of Fe10-Al14-Bgm with pressure causes monotonical decreases in the volumes of AO12 pseudo-dodecahedron and BO6 octahedron (V-A and V-B, respectively) as well as the associated A-O and B-O bond lengths. The interatomic angles of B-O1-B and B-O2-B decrease from 145.2-145.8 degrees at 4.2(1) GPa to 143.3-143.5 degrees at 64.6(6) GPa. Quantitative calculations of octahedral tilting angles (Phi) show that Phi increases smoothly with pressure. We found a linear relationship between the polyhedral volume ratio and the Phi in the bridgmanite with different compositions: V-A/V-B = -0.049 Phi + 5.549. Our results indicate an increased distortion of the Fe10-Al14-Bgm structure with pressure, which might be related to the distortion of A-site Fe2+. The local environmental changes of A-site Fe2+ in bridgmanite could explain previous results on the hyperfine parameters, abnormal lattice thermal conductivity, mean force constant of iron bonds and other physical properties, which in turn provide insights into our understanding on the geophysics and geochemistry of the planet.

Abstract Elastic properties of Si0.95H0.21O2 with hydrogarnet substitution (4H+ = Si4+) across the post‐stishovite transition (28–42 GPa) are determined up to 70 GPa using ab initio calculations and a pseudo‐proper type Landau model. At 28 GPa, elastic coefficients C11 and C12 converge, and the average shear and compressional velocity (VS and VP) decrease by a maximum of 25.5% and 5.2%, respectively. Hydrogarnet substitution reduces ambient elastic moduli and sound velocities, and shifts shear softening to lower pressure. 2%–13% Si0.95H0.21O2 may cause a VS anomaly of −0.5% to −2.6% at 700–820 km depth, explaining low VS layers beneath North America and the European Alps. Additionally, 20 vol % SiO2 in subducted basalt, with decreasing water content from 3.2 wt% to zero, could cause a VS anomaly of up to −7(4) % from 700 to 1,900 km depth, aligning with seismic scatterers identified in some subduction regions.

Molten silicates at depth are crucial for planetary evolution, yet their local structure and physical properties under extreme conditions remain elusive due to experimental challenges. In this study, we utilize in situ X-ray diffraction (XRD) at the Matter in Extreme Conditions (MEC) end-station of the Linear Coherent Linac Source (LCLS) at SLAC National Accelerator Laboratory to investigate liquid silicates. Using an ultrabright X-ray source and a high-power optical laser, we probed the local atomic arrangement of shock-compressed liquid (Mg,Fe)SiO3 with varying Fe content, at pressures from 81(9) to 385(40) GPa. We compared these findings to ab initio molecular dynamics simulations under similar conditions. Results indicate continuous densification of the O-O and Mg-Si networks beyond Earth’s interior pressure range, potentially altering melt properties at extreme conditions. This could have significant implications for early planetary evolution, leading to notable differences in differentiation processes between smaller rocky planets, such as Earth and Venus, and super-Earths, which are exoplanets with masses nearly three times that of Earth. Combining laser-driven shock compression and ultra-short X-ray pulses from LCLS, the local structure of liquid silicates was determined up to 385 GPa. Compared with molecular dynamics calculations, continuous densification of O-O and Mg-Si networks may alter melt properties and impact planetary differentiation.

Subducting slabs can transport water into the topmost lower mantle.This can have significant geophysical, geodynamic, and geochemical consequences including dehydration melting, formation of excess mantle minerals, and seismic anomalies.Seismic observations have indicated the existence of melt layers at topmost lower mantle likely associated with the slab subducting processes.In this presentation, we will examine the water solubility in mantle stishovite and bridgmanite and discuss how water affects the mineralogy and geophysical properties of subducting slab materials at the topmost lower mantle conditions.Al,Fe-bearing bridgmanite and Al-bearing stishovite, two major constituent minerals in subducted oceanic crust, can contain up to approximately 1000 ppm of water in relevant slab environments.When subducted crust undergoes partial melting and releases water, bridgmanite can become unstable and decompose into stishovite and ferropericlase in cold subducting slabs at the topmost lower mantle conditions.This can lead to formation of excess hydrated silica and the amount of stishovite will increase substantially in local regions.This can help explain the mineralogy of diamond inclusions from the lower mantle.We will also use modelled elasticity and sound velocities to address how the partial melting-induced dissociation and formation of minerals can lead to large velocity contrasts (particularly the contrast in V S ) that can help explain seismic observations of the region.

Combining the picosecond transient thermoreflectance (ps-TTR) and picosecond laser flash (ps-LF) techniques, we have developed a novel method to simultaneously measure the thermal effusivity and the thermal diffusivity of metal thin films and determine the thermal conductivity ($\kappa $& kappa;) and the heat capacity (${c_v}$cv) altogether. In order to validate our approach and evaluate the uncertainties, we analyzed five different metal films (Al, Cr, Ni, Pt, and Ti) with thicknesses ranging from 297 nm to 1.2 & mu;m. Our results on thermal transport properties and heat capacity are consistent with reference values, with the uncertainties for the thermal conductivity and the heat capacity measurements below 25% and 15%, respectively. Compared with the ps-TTR technique alone, the combined approach substantially lowers the uncertainty of the thermal conductivity measurement. Uncertainty analyses on various materials show that this combined approach is capable of measuring most of the materials with a wide range of thicknesses, including those with low thermal conductivity (e.g., mica) down to thicknesses as small as 60 nm and ultrahigh thermal conductivity materials (such as cubic BAs) down to 1400 nm. Simultaneous measurement of thermal conductivity and heat capacity enables exploration of the thermal physical behavior of materials under various thermodynamic and mechanical perturbations, with potential applications in thermal management materials, solid-state phase transitions, and beyond.

Thermoelastic properties of mantle candidate minerals are essential to our understanding of geophysical phenomena, geochemistry, and geodynamic evolutions of the silicate Earth. However, the lower-mantle mineralogy remains much debated due to the lack of single-crystal elastic moduli (C-ij) and aggregate sound velocities of (Al,Fe)-bearing bridgmanite, the most abundant mineral of the planet, at the lower mantle pressure-temperature (P-T) conditions. Here we report single-crystal C-ij of (Al,Fe)-bearing bridgmanite, Mg0.88Fe0.1Al0.14Si0.90O3 (Fe10-Al14-Bgm) with Fe3+/Sigma Fe = similar to 0.65, up to similar to 82 GPa using X-ray diffraction (XRD), Brillouin light scattering (BLS), and impulsive stimulated light scattering (ISLS) measurements in diamond-anvil cells (DACs). Two crystal platelets with orientations of (-0.50, 0.05, -0.86) and (0.65, -0.59, 0.48), that are sensitive to deriving all nine C-ij, are used for compressional and shear wave velocity (v(P) and v(S)) measurements as a function of azimuthal angles over 200 degrees at each experimental pressure. Our results show that all C-ij of singe-crystal Fe10-Al14-Bgm increase monotonically with pressure with small uncertainties of 1-2% (+/- 1 sigma), except C-55 and C-23, which have uncertainties of 3-4%. Using the third-order Eulerian finite-strain equations to model the elasticity data yields the aggregate adiabatic bulk and shear moduli and respective pressure derivatives at the reference pressure of 25 GPa: K-S = 326 +/- 4 GPa, mu = 211 +/- 2 GPa, K-s ' = 3.32 +/- 0.04, and mu ' = 1.66 +/- 0.02 GPa. The high-pressure aggregate v(S) and v(P) of Fe10-Al14-Bgm are 2.6-3.5% and 3.1-4.7% lower than those of MgSiO3 bridgmanite end-member, respectively. These data are used with literature reports on bridgmanite with different Fe and Al contents to quantitatively evaluate pressure and compositional effects on their elastic properties. Comparing with one-dimensional seismic profiles, our modeled velocity profiles of major lower-mantle mineral assemblages at relevant P-T suggest that the lower mantle could likely consist of about 89 vol% (Al,Fe)-bearing bridgmanite. After considering uncertainties, our best-fit model is still indistinguishable from pyrolitic or chondritic models.

In contrast to the Mott transition found in RNiO3 (R= rare earths), the metal-insulator transition temperature in the perovskite NaOsO3 is not sensitive to pressure. The peculiarity may be correlated to how the crystal structure of NaOsO3 responds to high pressure, which has been rarely studied so far. The pressure-induced bond-length shrinking can increase the orbital overlap integral and therefore the electron bandwidth. However, in the orthorhombic perovskite structure, the pressure-induced bending in the bond angle Os-O-Os may compensate for the bandwidth broadening due to the bond-length shrinking in some circumstances. A recent structural study on polycrystalline NaOsO3 indicated that orthorhombic distortion is enlarged under high pressure. But, how the local structure changes under pressure remains unknown. Moreover, a highly unusual phase transition from the orthorhombic phase (Pbnm) to a polar phase (Pbn21) occurs at around 18 GPa [Sereika et al., npj Quantum Mater. 5, 66 (2020)]. Motivated by these concerns, we have done a more comprehensive structural study on NaOsO3 using single-crystal diffraction with synchrotron radiation at high pressures up to 41 GPa. Diffraction patterns over the entire pressure range can be refined well with the Pbnm structural model. Moreover, the refinement results reveal in detail how the local structures change under pressure corresponding to the enhanced orthorhombic distortion from the lattice parameters. We have carried out a systematic study for understanding the pressure effect on the orthorhombic perovskites in the context of the influences of the charge distributions in the ABO3 formula, i.e., A3+B3+O3, A2+B4+O3, and A1+B5+O3 and the B-site cations from the 3d to the 4d and 5d row of elements. To fulfill this purpose, we have revisited two families of 3d perovskites: RCrO3 and RFeO3.

Abstract The post-stishovite transition is a classic pseudo-proper typed ferroelastic transition with a symmetry-breaking spontaneous strain. This transition has been studied using high-pressure spontaneous strains, optic modes, and elastic moduli (Cij) based on the Landau modeling, but its atomistic information and structural distortion remain poorly understood. Here we have conducted synchrotron single-crystal X-ray diffraction measurements on stishovite crystals up to 75.3 GPa in a diamond-anvil cell. Analysis of the data reveals atomic positions, bond lengths, bond angles, and variations of SiO6 octahedra across the transition at high pressure. Our results show that the O coordinates split at ~51.4 GPa, where the apical and equatorial Si-O bond lengths cross over, the SiO6 octahedral distortion vanishes, and the SiO6 octahedra start to rotate about the c axis. Moreover, distortion mode analysis shows that an in-plane stretching distortion (GM1+ mode) occurs in the stishovite structure at high pressure while a rotational distortion (GM2+ mode) becomes dominant in the post-stishovite structure. These results are used to correlate with elastic moduli and Landau parameters (symmetry-breaking strain e1–e2 and order parameter Q) to provide atomistic insight into the ferroelastic transition. When the bond lengths of two Si-O bonds are equal due to the contribution from the GM1+ stretching mode, C11 converges with C12, and the shear wave VS1[110] polarizing along [110] and propagating along [110] vanishes. Values of e1–e2 and Q are proportional to the SiO6 rotation angle from the occurrence of the GM1+ rotational mode in the post-stishovite structure. Our results on the pseudo-proper type transition are also compared with that for the proper type in albite and improper type in CaSiO3 perovskite. The symmetry-breaking strain, in all these types of transitions, arises as the primary effect from the structural angle (such as SiO6 rotation or lattice constant angle) and its relevant distortion mode in the low-symmetry ferroelastic phase.

Dense hydrous magnesium silicate (DHMS) phase E is a potential water carrier in subducting slabs that can transport water to the Earth's deep mantle between the bottom of the upper mantle and the uppermost transition zone. Therefore, knowledge on the high pressure‒temperature (P‒T) full elastic moduli of phase E at relevant mantle conditions is important in deciphering the existence of DHMS phases and their influences on seismic profiles in the region; however, the high P‒T elasticity data of phase E still remains lacking. In this work, we determined the combined effect of P‒T on the single‐crystal elasticity of phase E up to 24 GPa and 900 K by in situ X‐ray diffraction and Brillouin scattering measurements in externally‐heated diamond anvil cells. The aggregate elastic moduli and compressional‐wave (VP) and shear‐wave (VS) velocities of phase E are then derived by analyzing the single‐crystal elasticity and density data using the third‐order finite‐strain equations. We found that phase E exhibits much lower bulk and shear moduli and acoustic velocities than the most abundant constituent minerals in the upper mantle and transition zone, such as olivine, clinopyroxene, garnet, and wadsleyite. The modeled results using the obtained elasticity results show that the existence of phase E in a hydrated pyrolite model can result in relatively lower Vp and Vs profiles and negative velocity anomalies in seismic observations. The existence of phase E with relatively lower velocity profiles could be a possible origin of the low‐velocity layers atop the 410‐km discontinuity in some cold and highly‐hydrated regions.

Abstract Phase Egg and δ-AlOOH are two typical hydrous phases that might exist in the wet sedimentary layer of subducted slabs under mantle conditions. They are thus regarded as potential water carriers to Earth’s deep mantle. In this report, we report the full elastic constants of both phases determined by Brillouin scattering and X-ray diffraction measurements under ambient conditions. Our results indicate that the hydrogen-bond configurations in the crystal structures of the two phases have a profound effect on their principal elastic constants. The adiabatic bulk modulus (KS) and shear modulus (G) calculated from the obtained elastic constants using the Voigt-Reuss-Hill averaging scheme are 158.3(201) GPa and 123.0(60) GPa for phase Egg and 162.9(31) GPa and 145.2(13) GPa for δ-AlOOH, respectively. These results allow us to evaluate elastic moduli and sound velocities of hydrous minerals in the Al2O3-H2O-SiO2 ternary system (simplified composition of subducted wet sedimentary layer) at ambient conditions, including the contrast of the acoustic velocities VP and VS for the reaction AlSi3OH = δ-AlOOH + SiO2 (stishovite) and the evolution in the elastic moduli and sound velocities of hydrous minerals as a function of density.

Seismic studies have found seismic scatterers with −2 to −12% shear velocity anomalies along some subducting slabs at 700–1900 km depth. The ferroelastic post‐stishovite transition in subducted mid‐ocean ridge basalt (MORB) has been linked to these seismic features, but compressional and shear wave velocities (VP and VS) and full elastic moduli (Cij) of Al,H‐bearing stishovite and post‐stishovite at high pressure remain uncertain. Here we have determined Raman shifts of optic modes and equation of state parameters of two hydrated Al‐bearing stishovite crystals, Al1.3‐SiO2 (1.34 mol% Al and 0.55 mol% H) and Al2.1‐SiO2 (2.10 mol% Al and 0.59 mol% H), up to ∼70 GPa in diamond anvil cells coupled with Raman spectroscopy and X‐ray diffraction. The experimental data are modeled using a pseudoproper Landau theory to derive full Cij and sound velocities across the post‐stishovite transition at high pressure. The Al and H dissolution in stishovite significantly reduces the transition pressure to 21.1 GPa in Al1.3‐SiO2 and to 16.1 GPa in Al2.1‐SiO2, where the transition is manifested by approximately 29% VS reduction. Considering that stishovite with approximately 1.3 mol% Al and 0.6 mol% H could account for 20 vol% in subducted MORB at the top‐lower mantle, the Al,H‐bearing post‐stishovite transition with a Clapeyron slope of 65 K/GPa would occur at about 1060 km depth with −7(4)% VS anomaly. The VS anomalies across the Al,H‐bearing post‐stishovite transition can help explain the seismically‐observed depth‐dependent VS anomalies along some subducting slabs in the top‐ to mid‐lower‐mantle depths including the Tonga subducting slab.

Single‐crystal elasticity of both α ‐ and β ‐orthopyroxene was determined up to 20 GPa and 300 K by Brillouin scattering. Using the derived full elastic moduli ( C ij ), we investigated the contribution of the metastable pyroxene to the seismically observed 3%–5% low‐velocity anomalies along the subducting slab in the top transition zone. Our modeled results show that a harzburgite wedge with a 1000‐K colder geotherm and metastable α ‐orthopyroxene and olivine displays compressional ( V P ) and shear‐wave ( V S ) velocities 3.0%–3.6(6)% and 2.0%–2.8(6)% lower than the surrounding mantle at 410–460 km depth, respectively. At deeper depth up to 520 km, V P and V S of this metastable wedge with β ‐orthopyroxene and olivine are 3.6%–4.4(6)% and 2.8%–4.3(6)% lower than the pyrolitic mantle, respectively. The presence of both metastable orthopyroxene and olivine instead of metastable olivine alone helps better explain the origin of the low‐velocity anomalies within the subduction slab in the top transition zone.

Elastic moduli (C_{ij}) of single-crystal stishovite and post-stishovite are determined using Brillouin light scattering, impulsive stimulated light scattering, and x-ray diffraction up to 70 GPa. The C_{12} of stishovite converges with the C_{11} at ∼55  GPa, where the transverse wave V_{S1} propagating along [110] also vanishes. Landau modeling of the C_{ij}, B_{1g} optic mode, and lattice parameters reveals a pseudoproper type ferroelastic post-stishovite transition. The transition would cause peculiar anomalies in V_{S} and Poisson's ratio in silica-bearing subducting slabs in the mid-lower mantle.