Synchrotron X-ray Powder Diffraction Research Articles

Combined 7Li NMR, density functional theory and operando synchrotron X-ray powder diffraction to investigate a structural evolution of cathode material LiFeV2O7.

In our recent study, we demonstrated using 7Li solid-state Nuclear Magnetic Resonance (ssNMR) and single-crystal X-ray diffraction that the cathode LiFeV2O7 possesses a defect associated with the positioning of vanadium atoms. We proposed that this defect could be the source of extra signals detected in the 7Li spectra. In this context, we now apply density functional theory (DFT) calculations to assign the experimental signals observed in 7Li NMR spectra of the pristine sample. The calculation results are in strong agreement with the experimental observations. DFT calculations are a useful tool to interpret the observed paramagnetic shifts and understand how the presence of disorder affects the spectra behavior through the spin-density transfer processes. Furthermore, we conducted a detailed study of the lithiated phase combining operando synchrotron powder X-ray diffraction (SPXRD) and DFT calculations. A noticeable volume expansion is observed through the first discharge cycle which likely contributes to the enhanced lithium dynamics in the bulk material, as supported by previously published ssNMR data. DFT calculations are used to model the lithiated phase and demonstrate that both iron and vanadium participate in the redox process. The unusual electronic structure of the V4+ exhibits a single electron on the 3dxy orbital perpendicular to the V-O-Li bond being a source of a negative Fermi contact shift observed in the 7Li NMR of the lithiated phase.

Relationship Between Electronegativity of the Extra-Framework Cations and Adsorption Capacity for CO2 Gas on Mordenite Framework.

Synthetic mordenite is widely used as a molecular sieve, adsorbent, and catalyst. To enhance these functionalities, it is crucial to understand the ion-exchange properties and cation-exchange sites of the zeolite. In this study, we analyzed the structural changes in fully Cs-, Sr-, Cd-, and Pb-exchanged mordenite by using synchrotron X-ray powder diffraction under ambient conditions. Rietveld structure refinement revealed that the Cs+ cation is predominantly located near the 8-membered ring (8MR) due to its low electronegativity and hydration energy. In contrast, divalent cations such as Sr2+ and Cd2+ cations, with higher hydration energies compared to monovalent cations, are present as hydrated ions at the center of the 12-membered ring along the c-axis (12MRc). Pb2+ ions, due to their higher electronegativity than the framework atoms, exhibit a strong affinity for the electron cloud of framework oxygen atoms, which positions them close to the wall of the 12MRc. The observed differences in the locations of the extra-framework cations are attributed to electrostatic and hydration effects. Furthermore, the CO2 adsorption capacity was assessed based on the type and site of exchangeable cations. The findings indicate that an increase in the CO2 adsorption capacity correlates with the number of cations that can effectively interact with CO2.

Intrinsic electronic phase separation and competition between G -type, C -type, and CE -type charge and orbital ordering modes in Hg1−xNaxMn3Mn4O12

The novel series of hole-doped quadruple manganite perovskites Hg1−xNaxMn3Mn4O12 (HNMO) has been synthesized and its charge and orbital order behavior investigated through high-resolution synchrotron powder x-ray diffraction techniques. Through careful Rietveld refinements of structural models via symmetry-motivated approaches, we show that the ground state of HNMO compositions adopts a polar G-type charge and orbital ordered state, which is rare in manganite perovskites, and is robust as a sole phase up to a critical doping level. Upon this critical doping, coincident with that in which colossal magnetoresistance (CMR) is maximal in canonical manganite perovskites, electronic phase separation occurs between G-type and orbital order with charge disorder-type states. The latter state has recently been identified in Ca1−xNaxMn3Mn4O12 perovskites, and proposed to be the competing insulating state from which CMR phenomena emerge. We show that the mechanism for the formation of the G-type state is due to charge transfer processes which may occur through a coupling of distortions involving structural and charge and orbital degrees of freedom, ultimately driving the polar ground state through an improper-like ferroelectric polarization mechanism. These results will act as an important recipe for designing novel ferroelectric-active materials, in addition to expanding the richness of charge and orbital ordered states in manganite perovskites. Published by the American Physical Society 2024

Sn(SO4)2·2H2O from synchrotron powder data.

Tin(IV) sulfate dihydrate, Sn(SO4)2·2H2O, was prepared in a reflux of sulfuric acid under oxidizing conditions. Its crystal structure was determined from powder synchrotron X-ray diffraction data and is constructed of (100) layers of [SnO4(H2O)2] octa-hedra (point group symmetry 1) corner-connected by sulfate tetra-hedra. Hydrogen bonds of moderate strength between the water mol-ecules and sulfate O atoms hold the layers together.

Structure, and Phase Transformations of HPM-3: A Layered Precursor of the Neutral Aluminophosphate with JSN Topology.

The structure of HPM-3, a layered aluminophosphate prepared using 1,2,3-trimethylimidazolium (123TMI) as an organic structure-directing agent by the fluoride route, has been solved by continuous rotation electron diffraction (cRED), and Rietveld refined against synchrotron powder X-ray diffraction data. Charge balance of the occluded cation is achieved through F- anions and dangling Al(OP)3OH groups. Half of the Al is pentacoordinated in negatively charged Al(OP)4-F-Al(OP)4 pairs. The layers in HPM-3, denoted as jsn, are observed in the fully connected metalloaluminophosphate molecular sieves with JSN topology. Thus, HPM-3 can be a precursor to a JSN metal-free aluminophosphate if a topotactic condensation can be reached, which proved to be difficult but feasible. Treatments under different conditions resulted in a number of known (PST-27 and AlPO4-5 by a disruptive transformation) or new phases (through mild thermal treatments). Among the latter, a layered phase with a shorter interlayer space, denoted as HPM-3S, contains half the amount of organic as HPM-3. This is afforded by the capability of 123TMI compounds to sublimate at relatively low temperatures. HPM-3S still contains the same jsn layers. Therefore, the transformation of HPM-3 into HPM-3S is topotactic but without reaching condensation. Among the phases appearing under calcination conditions at relatively low temperature (<350 °C), we observed solids compatible with the JSN topology, but with poor crystallinity. This is attributed to a wrong alignment in HPM-3 of the dangling Al(OP)3OH and P(OAl)3═O that should connect adjacent layers in a topotactic condensation, which favors 1-dimensional stacking disorder by random shifts of layers during the thermal treatments. However, detemplation at a much lower temperature (175 °C) using O3 finally afforded an aluminophosphate molecular sieve with JSN topology with only moderate stacking disorder. This is just the third reported 2D-to-3D topotactic condensations in aluminophosphates.

Metastable Dihydrate of Sodium Chloride at Ambient Pressure.

Sodium chloride (NaCl) plays an important role in geochemistry, biology, industry, and food production, and it is among the most common salts in the solar system. Here, we report the discovery of a metastable NaCl dihydrate formed through rapid freezing (101-102 K s-1) of a NaCl solution at ambient pressure. Using synchrotron X-ray and neutron powder diffraction, we show that it transforms irreversibly to hydrohalite and ice Ih above 190 K upon heating and propose it is structurally related to hydrohalite with a 3 × 1 × 3 supercell as its unit cell. Calorimetric analyses reveal that the new hydrate transforms to hydrohalite with a heat release of -3.47 ± 0.55 kJ mol-1. The identification of this new NaCl dihydrate on the surfaces of icy worlds such as the moons of Jupiter and Saturn could indicate regions of recent activity where subsurface brines have frozen rapidly, priority targets for upcoming planetary missions.

Scalable and Efficient H2S Treated Nickel Foam Electrocatalyst for Alkaline Water Electrolysis Under Industrial Conditions

With the foreseen orders of magnitude increase of green hydrogen production from electrolysis in the coming decade [1], electrolyzer stacks must be produced in a scalable and efficiently manner based on abundant materials, while still maintaining high energy efficiency. This study explores a novel synthesis route utilizing reactive Chemical Vapor Deposition (CVD) of hydrogen sulfide (H2S) gas to enhance the catalytic activity of nickel foam for alkaline water electrolysis. The synthesis involves sulfiding the nickel foam at temperatures ranging from 100 °C to 140 °C in an H2S atmosphere for durations of 1 to 17 hours. The resulting electrodes exhibit a uniform film with distinctive nanostructural modification [2].Electrochemical performance evaluations were conducted under industrial conditions, in 30 wt% KOH electrolytes at 85 °C with current densities ranging from 200 to 500 mA/cm2 for up to two weeks. Testing under high current densities and elevated temperatures is essential to meet industrial requirements [3]. The tests were made in an immersed single cell setup with 4 cm2 electrodes on both sides [4]. Remarkably, the H2S-CVD modified electrodes demonstrate a cell potential reduction of 0.4 V@200 mA/cm2, corresponding to an 18% increase in the overall efficiency for water splitting compared to pristine nickel foam. Electrochemical analysis reveals a substantial 30-fold higher surface area following the H2S-CVD treatment. [2].Structural and compositional analyses of the modified nickel foam electrodes were conducted using various techniques including X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Energy Dispersive X-Rays (EDX) analysis, and synchrotron powder X-ray diffraction (XRD) both before and after running alkaline electrolysis. These analyses reveal the presence of Ni3S2 with a film thickness ranging from 1 to 4 μm post-H2S treatment. Characterization of the synchrotron data XRD shows 14 wt% Ni3S2 for the H2S-CVD treated samples. Furthermore, prolonged reaction times reveal the continuous reaction and emergence of NiS, elucidating the evolution of surface morphology under sulfidation conditions [2].Post-electrolysis characterizations indicate either the absence or minimal presence of sulfur on the modified electrodes, suggesting that the enhanced performance is likely attributed to alterations in the surface morphology rather than sulfur-assisted increase in the catalytic activity. This study provides insights into the surface-sensitive characterization, synthesis conditions, activity assessments, and degradation analyses, showing the potential of H2S-mediated surface modification as electrocatalytic material in alkaline water electrolysis systems. Bibliography [1] International Energy Agency. Global Hydrogen Review 2021. www.iea.org/report s/global-hydrogen-review-2021.[2] Olesen, S. E. et al. Scalable and Efficient H2S Treatment of Nickel Foam Electrocatalyst for Alkaline Water Electrolysis under Industrial Conditions. 2024. In preparation.[3] Ehlers, J. C.; Feidenhans’l, A. A.; Therkildsen, K. T.; Larrazábal, G. O. Affordable Green Hydrogen from Alkaline Water Electrolysis: Key Research Needs from an Industrial Perspective. ACS Energy Letters. American Chemical Society March 10, 2023, pp 1502–1509. doi.org/10.1021/acsenergylett.2c02897.[4] Frederiksen, M. L.; Kragh-Schwarz, M. V.; Bentien, A.; Nielsen, L. P. Improved Performance of Electrodes for Alkaline Electrolysis. Transactions of the Institute of Metal Finishing. 2023. 10.1080/00202967.2023.2196850. Figure 1

Does Trapped Oxygen Form in the Bulk of LiNiO2 during Charging?

LiNiO₂ remains a critical archetypal material for high energy density Li-ion batteries, forming the basis of Ni-rich cathodes in use today.1-4 Nevertheless, there are still uncertainties surrounding the charging mechanism at high states of charge and the potential role of oxygen redox.5-11 Substantial efforts have been made to understand these phenomena and the structural transitions that take place when Li is extracted from LiNiO₂, but there remains considerable debate over the extent of Ni oxidation and O-redox in LiNiO₂.4-11 Recent research into O oxidation in Li-rich cathodes, such as Li1.2Ni0.13Co0.13Mn0.54O2, has indicated that oxidised oxygen takes the form of molecular O2, which is trapped within vacancy clusters in the cathode structure.12 However, in the case of stoichiometric materials like LiNiO2, it has been argued that this same mechanism cannot apply due to the lack of transition metal vacancies in the fully dense transition metal layers (in the Li-rich materials the Li in the transition metal layers are removed on charge and the remaining vacancies cluster to accommodate the O2.11 In this study we show that oxidation of the oxide ions forms O₂ trapped in the particles and is accompanied by the formation of 8% Ni vacancies on the transition metal sites of previously fully dense transition metal layers. High resolution resonant inelastic X-ray scattering (RIXS) at the O K-edge confirms the presence of trapped molecular O₂, corresponding to approximately 2% of the O in the material. We employ a combination of neutron and synchrotron X-ray powder diffraction analysis that takes account of the stacking faults prevalent in these charged materials, showing that 8% Ni vacancies form in the originally fully dense transition metal layer. Such Ni vacancy formation on charging activates O-redox by generating non-bonding O 2p orbitals and is necessary to form vacancy clusters to accommodate O₂ in the particles. Ni accumulates at and near the surface of the particles on charging, forming a Ni-rich shell approximately 5 nm thick; enhanced by loss of O₂ from the surface. Our study shows the mechanism of O-redox involving the formation of trapped O₂ in the bulk is general to both Li-rich materials and LiNiO₂ despite the latter possessing fully dense transition metal layers in the pristine state.1. F. Schipper, E. M. Erickson, C. Erk, J.-Y. Shin, F. F. Chesneau and D. Aurbach, J. Electrochem. Soc., 2017, 164, A6220.2. S. G. Booth, et al., APL Mater., 2021, 9, 109201.3. M. Bianchini, M. Roca-Ayats, P. Hartmann, T. Brezesinski and J. Janek, Angew. Chem.,Int. Ed., 2019, 58, 10434–10458. 6 C. S. Yoon, D. W. Jun, S. T. Myung and Y. K. Sun, ACS Energy Lett., 2017, 2, 1150–1155.4. C. Xu, P. J. Reeves, Q. Jacquet and C. P. Grey, Adv. Energy Mater., 2021, 11, 2003404.5. Juelsholt, J. Chen, M. A. Pérez-Osorio, G. J. Rees, S. De Sousa Coutinho, H. E. Maynard-Casely, J. Liu, M. Everett, S. Agrestini, M. Garcia-Fernandez, K.-J. Zhou, R. House and P. G. Bruce, Energy Environ Sci, 2024.6. F. Kong, C. Liang, L. Wang, Y. Zheng, S. Perananthan, R. C. Longo, J. P. Ferraris, M. Kim and K. Cho, Adv. Energy Mater., 2019, 9, 1802586.7. Dm. M. Korotin, D. Novoselov and V. I. Anisimov, Phys Rev B, 2019, 99, 45106.8. K. Foyevtsova, I. Elfimov, J. Rottler and G. A. Sawatzky, Phys Rev B, 2019, 100, 165104.9. N. Li, S. Sallis, J. K. Papp, B. D. McCloskey, W. Yang and W. Tong, Nano Energy, 2020, 78, 105365.10 A. R. Genreith-Schriever, H. Banerjee, A. S. Menon, E. N. Bassey, L. F. J. Piper, C. P. Grey and A. J. Morris, Joule, 2023, 7, 1623–1640.11. A. S. Menon, B. J. Johnston, S. G. Booth, L. Zhang, K. Kress, B. E. Murdock, G. Paez Fajardo, N. N. Anthonisamy, N. Tapia-Ruiz, S. Agrestini, M. Garcia-Fernandez, K. Zhou, P. K. Thakur, T. L. Lee, A. J. Nedoma, S. A. Cussen and L. F. J. Piper, PRX Energy, 2023, 2, 13005.12. R. A. House, J. J. Marie, M. A. Pérez-Osorio, G. J. Rees, E. Boivin and P. G. Bruce, Nat Energy, 2021, 6, 781–789. Figure 1

Role of Na2CO3 as Nucleation Seeds to Accelerate the CO2 Uptake Kinetics of MgO-Based Sorbents.

There is an urgent need for inexpensive, functional materials that can capture and release CO2 under industrial conditions. In this context, MgO is a highly promising, earth-abundant CO2 sorbent. However, despite its favorable carbonation thermodynamics and potential for high gravimetric CO2 uptakes, MgO-based CO2 sorbents feature slow carbonation kinetics, limiting their CO2 uptake during typical industrial contact times. The addition of molten alkali metal nitrate promoters, such as NaNO3, can partially mitigate the slow kinetics. Here, we investigate how the CO2 uptake kinetics of NaNO3-promoted MgO can be increased further through the addition of finely dispersed Na2CO3. The incorporation of Na2CO3 significantly increases the CO2 uptake rate from 1.4 to 14.6 mmol MgCO3 (mol MgO)-1 s-1. Using in situ synchrotron X-ray powder diffraction (XRD), we track the formation of MgCO3 and elucidate the mechanism through which Na2CO3 promotes the CO2 uptake of MgO. Our findings demonstrate that Na2CO3 rapidly converts within seconds into Na2Mg(CO3)2 during carbonation, acting subsequently as nucleation seeds for MgCO3 formation, in turn significantly enhancing CO2 uptake kinetics. Further, the presence of Na2Mg(CO3)2 considerably enhances the mobility of ions in the sorbent, leading to sintering of MgCO3. Importantly, Na2Mg(CO3)2 promotes MgCO3 formation even in the presence of molten RbNO3, a salt with a limited ability to dissolve [Mg2+···CO3 2-] ion pairs, indicating that Na2Mg(CO3)2 lowers the critical ion pair concentration required for MgCO3 nucleation. Additionally, the partial dissolution of Na2CO3 in NaNO3 may increase the concentration of carbonate ions in the melt, further accelerating carbonation kinetics in MgO-(Na2CO3/NaNO3).

Position-independent product increase rate in a shaker mill revealed by position-resolved in situ synchrotron powder X-ray diffraction

We investigated the position and time dependence of a mechanochemical reaction induced by ball milling using in situ synchrotron powder X-ray diffraction with changing X-ray irradiation position. The mechanochemical reduction of AgCl with Cu was monitored in situ with the X-rays incident at two different vertical positions on the jar. Our previously developed multi-distance Rietveld method was applied to analyze the in situ diffraction data with a 1 min resolution. Both the vertical and the horizontal sample positions were determined using the sample-to-detector distances from the in situ data. Position dependence was found in the powder spreading and induction time. We reveal that the increase rate of the product is independent of the sample position when measured with a 1 min time resolution, confirming the validity of in situ monitoring of part of the space in a milling jar for a gradual mechanochemical reaction.

Identification of the high-pressure phases of [formula omitted]-SnWO4 combining x-ray diffraction and crystal structure prediction

We have characterized the high-pressure behavior of α-SnWO4. The compound has been studied up to 30 GPa using a diamond-anvil cell and synchrotron powder X-ray diffraction. We report evidence of two structural phase transitions in the pressure range covered in our study, and we propose a crystal structure for the two high-pressure phases. The first one, observed around 12.9 GPa, has been obtained combining indexation using DICVOL and density-functional theory calculations. The second high-pressure phase, observed around 17.5 GPa, has been determined by using the CALYPSO code, the prediction of which was supported by a Le Bail fit to the experimental X-ray diffraction patterns. The proposed structural sequence involves two successive collapses of the unit-cell volume and an increase in the coordination number of Sn and W atoms. The room-temperature equations of state, the principal axes of compression and their compressibility, the elastic constants, and the elastic moduli are reported for α-SnWO4 and for the two high-pressure phases.

Crystal structure of cariprazine dihydrochloride, C21H34Cl2N4OCl2

The crystal structure of cariprazine dihydrochloride has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Cariprazine dihydrochloride crystallizes in space group P21/n (#14) with a = 27.26430(14), b = 7.29241(1), c = 12.80879(4) Å, β = 99.5963(2)°, V = 2511.038(8) Å3, and Z = 4 at 295 K. The crystal structure consists of layers of cations parallel to the bc-plane. The cations stack along the b-axis. Each H atom on the two protonated N atoms participates in a discrete N–H⋯Cl hydrogen bond. One Cl anion acts as an acceptor in two of these bonds, while the other Cl is an acceptor in only one bond. The result is to link the cations and anions into columns parallel to the b-axis. The powder pattern has been submitted to the ICDD for inclusion in the Powder Diffraction File™ (PDF®).

Mechanochemical Synthesis and Magnetic Properties of the Mixed-Valent Binary Silver(I,II) Fluorides, AgI2AgIIF4 and AgIAgIIF3.

Fluoridoargentates(II) represent a fascinating class of silver(II) compounds with structural and magnetic similarities to cuprate superconductors. However, their synthesis is challenging, leaving their properties largely underexplored and hindering the discovery of new phases. This study introduces mechanochemistry as a novel approach for the synthesis of fluoridoargentates(II), avoiding the use of anhydrous HF or elemental fluorine and employing readily available equipment. Notably, ball milling of commercially available precursors successfully produced the long-sought-after first two examples of binary mixed-valent silver(I,II) phases, AgI2AgIIF4 (Ag3F4) and AgIAgIIF3 (Ag2F3). While the AgI2AgIIF4 phase was obtained at room temperature, the AgIAgIIF3 phase is metastable and required milling under cryogenic conditions. Characterization by synchrotron powder X-ray and neutron diffraction revealed that AgI2AgIIF4 crystallizes in the P21/c space group and is isostructural to β-K2AgF4. In this crystal structure, [AgIIF2F4/2]2- distorted octahedral units with 4 + 2 coordination, extend parallel to a-crystallographic axis giving a quasi-one-dimensional canted antiferromagnetic character, as shown by magnetic susceptibility. The triclinic perovskite AgIAgIIF3 phase adopts the P1̅ space group, is isostructural to AgCuF3 and also shows features of a one-dimensional antiferromagnet. This mechanochemical approach, also successfully applied to synthesize β-K2AgF4, is expected to expand the field of silver(II) chemistry, accelerating the search for silver analogs to cuprate superconductors and potentially extending to other cations in unusual oxidation states.

Br-Induced Suppression of Low-Temperature Phase Transitions in Mixed-Cation Mixed-Halide Perovskites.

Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs y FA1-y Pb(Br x I1-x )3 using low-temperature in situ synchrotron powder X-ray diffraction. Our findings revealed that substituting the I anion with Br in mixed-cation (Cs,FA) perovskites suppressed the phase transformation from tetragonal to orthorhombic at low temperatures. The addition of Br also prevented the formation of nonperovskite secondary phases. We gained fundamental insights into the structural behavior of these materials by creating a low-temperature phase diagram for the compositional set of mixed-cation mixed-halides. This understanding of the structural properties lays the groundwork for designing more robust and efficient energy materials capable of functioning under extreme temperature conditions, including space-based solar energy conversion.

Crystal structure of racemic benserazide hydrochloride Form I, C10H16N3O5Cl

The crystal structure of benserazide hydrochloride Form I has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Benserazide hydrochloride Form I crystallizes in space group P21/n (#14) with a = 19.22983(15), b = 14.45066(10), c = 4.57982(2) Å, β = 93.6935(3), V = 1270.014(15) Å3, and Z = 4 at 295 K. The crystal structure contains pairs of hydrogen-bonded benserazide cations, which are hydrogen bonded to chloride anions, resulting in chains along the c-axis. In addition, O–H⋯Cl, N–H⋯O, O–H⋯N, and O–H⋯O hydrogen bonds link the cations and anions into a three-dimensional framework. The powder pattern has been submitted to ICDD® for inclusion in the Powder Diffraction File™ (PDF®).

Anomalous lattice contraction and emerging topological phases in Bi-substituted Sm2Ir2O7

We demonstrate that substituting Bi for Sm in the pyrochlore Sm$_2$Ir$_2$O$_7$ induces an anomalous lattice contraction, with $\Delta a \sim -0.012$~\AA~observed at 10\% Bi substitution, where 'a' denotes the lattice constant. Beyond 10\% Bi substitution, the lattice expands according to Vegard's law. Within this anomalous substitution range, the resistivity shows a 1/T behavior up to 2\% Bi-substitution, while near 10\% substitution a -lnT dependence is observed. These resistivity behaviors suggest the possibility of a Weyl phase up to 2\% Bi substitution, which transforms to a semimetallic quadratic band touching (QBT) topological phase near 10\%. For the intermediate composition (Sm$_{0.95}$Bi$_{0.05}$)$_2$Ir$_2$O$_7$, the resistivity scales as $\rm 1/T^{1/4}$, possibly due to its proximity to a proposed quantum critical point at the Weyl-QBT phase boundary [Phys. Rev. X 4, 041027 (2014)]. The samples were characterized using synchrotron powder X-ray diffraction, X-ray near-edge fine structure (XANES), and Extended X-ray absorption fine structure (EXAFS) probes. Additionally, magnetic susceptibility and heat capacity measurements were conducted to provide further support.

B-site ordered and disordered phases in A-site columnar-ordered quadruple perovskites Nd2MnMn(Mn4−xSbx)O12

Solid solutions Nd2MnMn(Mn4−xSbx)O12, belonging to the A-site columnar-ordered quadruple perovskite subfamily A2A′A″B4O12 and prepared by a high-pressure, high-temperature method at about 6 GPa and about 1700 K, were investigated in a compositional range of 0.2 ≤ x ≤ 2.0. Crystal structures were studied using synchrotron powder X-ray diffraction. Two regions with different cation orders in the B sublattice were found: a narrow region of 0.8 ≤ x ≤ 1.0 had a B-site disordered structure with space group P42/nmc (No. 137), and a wider region of 1.6 ≤ x ≤ 2.0 had a B-site rock-salt-ordered structure with space group P42/n (No. 86). Small anti-site disorder of Nd and Mn was detected among the A, A′, and A″ sites. In the B-site rock-salt-ordered structures, one B site was solely occupied by Mn, the second B′ site had a mixture of Sb and Mn (for x < 2). The samples showed complex magnetic behavior with two ferrimagnetic transitions. TC1 monotonically increased (from 66 K to 75 K) and TC2 was almost constant (about 6–7 K) for 0.8 ≤ x ≤ 1.0. TC1 monotonically decreased (from 77 K to 63 K) and TC2 monotonically increased (from 19 K to 39 K) for 1.6 ≤ x ≤ 2.0. There was evidence for the third magnetic transition in the 1.7 ≤ x ≤ 2.0 samples, and TC3 increased from 13 K to 20 K with increasing x.

Single-Crystalline 3D Covalent Organic Frameworks with Exceptionally High Specific Surface Areas and Gas Storage Capacities.

Single-crystalline covalent organic frameworks (COFs) are highly desirable toward understanding their pore chemistry and functions. Herein, two 50-100 μm single-crystalline three-dimensional (3D) COFs, TAM-TFPB-COF and TAPB-TFS-COF, were prepared from the condensation of 4,4',4″,4‴-methanetetrayltetraaniline (TAM) with 3,3',5,5'-tetrakis(4-formylphenyl)bimesityl (TFPB) and 3,3',5,5'-tetrakis(4-aminophenyl)bimesityl (TAPB) with 4,4',4″,4‴-silanetetrayltetrabenzaldehyde (TFS), respectively, in 1,4-dioxane under the catalysis of acetic acid. Single-crystal 3D electron diffraction reveals the triply interpenetrated dia-b networks of TAM-TFPB-COF with atom resolution, while the isostructure of TAPB-TFS-COF was disclosed by synchrotron single-crystal X-ray diffraction and synchrotron powder X-ray diffraction with Le Bail refinements. The nitrogen sorption measurements at 77 K disclose the microporosity nature of both activated COFs with their exceptionally high Brunauer-Emmett-Teller surface areas of 3533 and 4107 m2 g-1, representing the thus far record high specific surface area among imine-bonded COFs. This enables the activated COFs to exhibit also the record high methane uptake capacities up to 28.9 wt % (570 cm3 g-1) at 25 °C and 200 bar among all COFs reported thus far. This work not only presents the structures of two single-crystalline COFs with exceptional microporosity but also provides an example of atom engineering to adjust permanent microporous structures for methane storage.

Pressure-induced anomaly of transport properties and structural transition in layered ferromagnetic metal TlCo2S2

In this work, the structural and transport properties of ferromagnetic metal TlCo2S2 with ThCr2Si2-type crystal structure are systematically studied using high-pressure synchrotron x-ray powder diffraction, electrical transport measurements and first-principles calculations. All the resistances of TlCo2S2 between 1.4 GPa and 5.2 GPa exhibit an upturn at TS and an obvious hysteresis is observed below TS when measured in the cooling and heating processes. As the pressure increases, TS gradually increases and the resistances display a metallic behavior without any anomaly in the whole temperature region above 5.2 GPa, indicating that a possible structural phase transition occurs at TS and is beyond the room temperature above 5.2 GPa. High-pressure x-ray diffraction measurements combined with crystal structure prediction indicate that at room temperature TlCo2S2 undergoes a structural phase transition from a tetragonal phase (I4/mmm) to an orthorhombic structure (Bmab) at Pc ≈6.8 GPa, which is consistent with the results of the resistances under high pressure. Our results indicate that a first-order structural phase transition of TlCo2S2 is induced by high pressure and then results in the anomaly of the electrical transport properties.

Pressure-induced multiple structural phase transitions on multiferroic CaMn7O12

CaMn7O12 (CMO) is an outstanding multiferroic material known for its significant magnetically-induced electric polarization. Its strong magnetoelectric (ME) effect, i.e., electric polarization controlled via magnetic fields or vice versa, makes this material suitable for a variety of technological applications. In this study, we employed synchrotron X-ray powder diffraction to explore polycrystalline CMO's pressure-induced structural phase transitions (SPTs). Our results indicate that CMO undergoes two distinct pressure-induced SPTs: the first transition occurs at pressures above 7.0 GPa, changing from a rhombohedral to an orthorhombic structure, and the second occurs around 13.0 GPa, transforming into a monoclinic structure. These findings differ from the pressure-induced behavior of CMO single crystals and highlight CMO as one of the rare quadruple perovskites exhibiting multiple pressure-induced non-isostructural phase transitions. This study expands the understanding of phase stability behavior in multiferroic materials under high-pressure conditions.