High-pressure synchrotron X-ray powder diffraction studies of smectite group minerals (beidellite, montmorillonite, and nontronite) reveal comparative volumetric changes in the presence of different fluids, as pressure transmitting media (PTM) of silicone oil and distilled water for anhydrous and hydrous environments at room temperature. Using silicone oil PTM, all minerals show gradual contraction of unit-cell volumes and atomistic interplane distances. They, however, show abrupt collapse near 1.0 GPa under distilled water conditions due to hydrostatic to quasi-hydrostatic environmental changes of water PTM around samples concomitant with the transition from liquid to ICE-VI and ICE-VII. The degrees of volume contractions of beidellite, montmorillonite, and nontronite up to ca. 3 GPa are ca. 6.6%, 8.9%, and 7.5% with bulk moduli of ca. 38(1) GPa, 31(2) GPa, and 26(1) GPa under silicone oil pressure, whereas 13(1) GPa, 13(2) GPa, and 17(2) GPa, and 17(1) GPa, 20(1) GPa, and 21(1) GPa under hydrostatic and quasi-hydrostatic environments before and after 1.50 GPa, respectively.

The spin-orbit entangled (SOE) $J_{\mathrm{eff}}$ state has been a fertile ground to study quantum phenomena. Contrary to the conventional weakly correlated $J_{\mathrm{eff}}=1/2$ state of $4d$ and $5d$ transition metal compounds, the ground state of $\mathrm{Cu}{\mathrm{Al}}_2{\mathrm{O}}_4$ hosts a $J_{\mathrm{eff}}=1/2$ state with a strong correlation of Coulomb $U$. Here, we report that, surprisingly, ${\mathrm{Cu}}^{2+}$ ions of $\mathrm{Cu}{\mathrm{Al}}_2{\mathrm{O}}_4$ overcome the otherwise usually strong Jahn-Teller distortion and instead stabilize the SOE state, although the cuprate has relatively small spin-orbit coupling. From the x-ray absorption spectroscopy and high-pressure x-ray diffraction studies, we obtained definite evidence of the $J_{\mathrm{eff}}=1/2$ state with a cubic lattice at ambient pressure. We also found the pressure-induced structural transition to a compressed tetragonal lattice consisting of the spin-only $S=1/2$ state for pressure $P_c>8\mathrm{GPa}$. This phase transition from the Mott insulating $J_{\mathrm{eff}}=1/2$ to the $S=1/2$ states is a unique phenomenon. Our study offers an example of the SOE $J_{\mathrm{eff}}$ state under strong electron correlation and its pressure-induced transition to the $S=1/2$ state.

The geochemistry and mineralogy of Mn nodules offer crucial insights into the origins, environmental changes, and distribution of abyssal resources. However, the conventional laboratory X-ray diffractometer, usually employed for semi-quantitative analysis of mineral composition in Mn nodules, often fails to sufficiently detect minor phases due to beam flux limitations and high background signals. In this study, we investigated differences in manganate composition, even when comprising around 1% of the phase fraction, in two manganese nodules (KC-8 and KODOS-10) using high-resolution synchrotron X-ray diffraction. The Mn/Fe ratios of KC-8 and KODOS-10 were 1.32 and 6.24, respectively, indicating that KC-8 and KODOS-10 were predominantly formed in hydrogenetic and diagenetic environments. Both samples contained quartz, vernadite, buserite, and feldspar. Todorokite and illite were exclusively observed in KODOS-10. In KC-8, the phase fractions of vernadite and buserite among manganates ranged from 94(5)%–100(4)% and 6(1)%–0%, respectively. However, in KODOS-10, the fractions of vernadite, buserite, and todorokite ranged from 47(1)%–56(2)%, 33.6(4)%–40.1(3)%, and 10(3)%–16.3(8)%, respectively.

Biotite, a phyllosilicate mineral, possesses significant potential for cesium (Cs) adsorption owing to its negative surface charge, specific surface area (SSA), and frayed edge sites (FES). Notably, FES are known to play an important role in the adsorption of Cs. The objectives of this study were to investigate the Cs adsorption capacity and behavior of artificially weathered biotite and identify mineralogical characteristics for the development of an eco-friendly geologically-based Cs adsorbent. Through various analyses, it was confirmed that the FES of biotite was mainly formed by mineral structural distortion during artificial weathering. The Cs adsorption capacity is improved by approximately 39% (from 20.53 to 28.63 mg g^-1) when FES are formed in biotite through artificial weathering using a low-concentration acidic solution mixed with hydrogen peroxide (H₂O₂). Especially, the Cs selectivity in Cs-containing seawater, including high concentrations of cations and organic matter, was significantly enhanced from 203.2 to 1707.6 mL g^-1, an increase in removal efficiency from 49.5 to 89.2%. These results indicate that FES of artificially weathered biotite play an essential role in Cs adsorption. Therefore, this simple and economical weathering method, which uses a low-concentration acidic solution mixed with H₂O₂, can be applied to natural minerals for use as Cs adsorbents.

We report comparative structural changes of potassium-contained zeolite-W (K-MER, structural analogue of natural zeolite merlinoite) and monovalent extra-framework cation (EFC)-exchanged M-MERs (M = Li⁺, Na⁺, Ag⁺, and Rb⁺). High-resolution synchrotron X-ray powder diffraction study precisely determines that crystal symmetry of MERs is tetragonal (I4/mmm). Rietveld refinement results reveal that frameworks of all MERs are geometrically composed of disordered Al/Si tetrahedra, bridged by linkage oxygen atoms. We observe a structural relationship between a group of Li-, Na-, and Ag-MER and the group of K- and Rb-MER by EFC radius and position of M(1) site inside double 8-membered ring unit (d8r). In the former group, a-axes decrease reciprocally, c-axes gradually extend by EFC size, and M(1) cations are located at the middle of the d8r. In the latter group, a- and c-axes lengths become longer and shorter, respectively, than axes of the former group, and these axial changes come from middle-to-edge migration of M(1) cations inside the d8r channel. Unit cell volumes of the Na-, Ag-, and K-MER are ca. 2005 ų, and the volume expansion in the MER series is limited by EFC size, the number of water molecules, and the distribution of extra-framework species inside the MER channel. EFC sites of M(1) and M(2) show disordered and ordered distribution in the former group, and all EFC sites change to disordered distribution after migration of the M(1) site in the latter group. The amount of water molecules and porosities are inversely proportional to EFC size due to the limitation of volume expansion of MERs. The channel opening area of a pau composite building unit and the amount of water molecules are universally related as a function of cation size because water molecules are mainly distributed inside a pau channel.

This paper aimed to investigate the structural and chemical changes of Ag-natrolite (Ag₁₆Al₁₆Si₂₄O₈₀·16H₂O, Ag-NAT) in the presence of different pressure transmitting mediums (PTMs), such as N₂, O₂ and CH₄, up to ~8 GPa and 250 °C using in situ synchrotron X-ray powder diffraction and Rietveld refinement. Pressure-induced insertion occurs in two stages in the case of N₂ and O₂ runs, as opposed to the CH₄ run. First changes of the unit cell volume in N₂, O₂ and CH₄ runs are observed at 0.88(5) GPa, 1.05(5) GPa and 1.84(5) GPa with increase of 5.7(1)%, 5.5(1)% and 5.7(1)%, respectively. Subsequent volume changes of Ag-natrolite in the presence of N₂ and O₂ appear at 2.15(5) GPa and 5.24(5) GPa with a volume increase of 0.8(1)% and a decrease of 3.0(1)%, respectively. The bulk moduli of the Ag-NAT change from 42(1) to 49(7), from 38(1) to 227(1) and from 49(3) to 79(2) in the case of N₂, O₂ and CH₄ runs, respectively, revealing that the Ag-NAT becomes more incompressible after each insertion of PTM molecules. The shape of the channel window of the Ag-NAT changes from elliptical to more circular after the uptake of N₂, O₂ and CH₄. Overall, the experimental results of Ag-NAT from our previous data and this work establish that the onset pressure exponentially increases with the molecular size. The unit cell volumes of the expanded (or contracted) phases of the Ag-NAT have a linear relationship and limit to maximally expand and contract upon pressure-induced insertion.