Spin-mediated shear oscillators in a van der Waals antiferromagnet.

Understanding how microscopic spin configuration gives rise to exotic properties at the macroscopic length scale has long been pursued in magnetic materials1-5. One seminal example is the Einstein-de Haas effect in ferromagnets1,6,7, in which angular momentum of spins can be converted into mechanical rotation of an entire object. However, for antiferromagnets without net magnetic moment, how spin ordering couples to macroscopic movement remains elusive. Here we observed a seesaw-like rotation of reciprocal lattice peaks of an antiferromagnetic nanolayer film, whose gigahertz structural resonance exhibits more than an order-of-magnitude amplification after cooling below the Néel temperature. Using a suite of ultrafast diffraction and microscopy techniques, we directly visualize this spin-driven rotation in reciprocal space at the nanoscale. This motion corresponds to interlayer shear in real space, in which individual micro-patches of the film behave as coherent oscillators that are phase-locked and shear along the same in-plane axis. Using time-resolved optical polarimetry, we further show that the enhanced mechanical response strongly correlates with ultrafast demagnetization, which releases elastic energy stored in local strain gradients to drive the oscillators. Our work not only offers the first microscopic view of spin-mediated mechanical motion of an antiferromagnet but it also identifies a new route towards realizing high-frequency resonators8,9 up to the millimetre band, so the capability of controlling magnetic states on the ultrafast timescale10-13 can be readily transferred to engineering the mechanical properties of nanodevices.

Design Strategies of Spinel Oxide Frameworks Enabling Reversible Mg-Ion Intercalation.

ConspectusReversible Mg2+ intercalation in metal oxide frameworks is a key enabler for an operational Mg-ion battery with high energy density needed for the next generation of energy storage technologies. While functional Mg-ion batteries have been achieved in structures with soft anions (e.g., S2- and Se2-), they do not meet energy density requirements to compete with the current rechargeable lithium-ion batteries due to their low insertion potentials. It emphasizes the necessity of finding an oxide-based cathode that operates at high potentials. A leading hypothesis to explain the limited availability of oxide Mg-ion cathodes is the belief that Mg2+ has sluggish diffusion kinetics in oxides due to strong electrostatic interactions between the Mg2+ ions and oxide anions in the lattice. From this assessment, it can be hypothesized that such rate limiting kinetic shortcomings can be mitigated by tailoring an oxide framework through creating less stable Mg2+-O2- coordination.Based on theoretical calculations and preliminary experimental data, oxide spinels have been identified as promising cathode candidates with storage capacity, insertion potential, and cation mobility that meet the requirements for a secondary Mg-ion battery. However, spinels with a single redox metal, such as MgCr2O4 or MgMn2O4, were not found to demonstrate sufficiently reversible Mg-ion intercalation at high redox potentials when coupled with nonaqueous Mg-electrolytes. Therefore, a materials development effort was initiated to design, synthesize, and evaluate a new class of solid-solution oxide spinels that can satisfy the required properties needed to create a sustainable Mg-ion cathode. These were designed by bringing together electrochemically active metals with stable redox potentials and charged states against the electrolyte, for instance, Mn3+, in combination with a structural stabilization component, typically Cr3+. Furthermore, common spinel structural defects that degrade performance, i.e., antisite inversion, were controlled to see correlation between structures and electrochemical overpotentials, thus controlling overall hysteresis. The designed materials were characterized by both short- and long-range structure in both ex situ and in situ modes to confirm the nature of solid-solution and to correlate structural changes and redox activity to electrochemical performance. Consistent and reproducible results were observed for facile bulk Mg2+-ion activity without phase transformations, leading to enhanced energy storage capability based on reversible intercalation of Mg2+, enabled by understanding the variables that control the electrochemical performance of the spinel oxide. Based on these observations, with proper materials design, it is possible to develop an oxide cathode material that has many of the desired properties of a Li-ion intercalation cathode, representing a significant mile marker in the quest for high energy density Mg-ion batteries.This Account describes strategies for the design and development of new spinel oxide intercalation materials for high-energy Mg-ion battery cathodes through a combination of theoretical and experimental approaches. We will review the key factors that govern the kinetics of Mg2+ diffusion in spinel oxides and illustrate how material complexity correlates with the electrochemical Mg2+ activity in oxides and is supported by secondary characterization. The understanding gained from the fundamental studies of cation diffusion in oxide cathodes will be beneficial for chemists and materials scientists who are developing rechargeable batteries.

Monitoring Structural Changes during Electrochemical Cycling of Solid-Solution Spinel Oxide MgCrVO4.

Rechargeable magnesium-ion batteries (MIBs) hold significant promise as an alternative to conventional lithium-ion technology driven by their natural abundance and low-cost, high-energy density, and safety features. Spinel oxides, including MgCrVO4, have emerged as a prospective cathode material for MIBs due to their promising combination of capacity, operating potential, and cation mobility. However, the structural evolution, phase stability, and processes of Mg mobility in MgCrVO4 during electrochemical cycling are poorly understood. In this study, we synthesized a single-phase, solid solution of spinel oxide MgCrVO4 and employed operando X-ray diffraction to couple physical properties with structural changes during cycling. Our results revealed a two-phase reaction mechanism coupled with a solid-solution-like reaction, highlighting the complicated transformation between two distinct phases in the MgCrVO4 lattice during Mg (de)intercalation. Rietveld refinement of the operando data provided valuable insights into the mechanism of the Cr/V-based spinel oxide, shedding light on the transition between the two phases and their roles in Mg-ion (de)intercalation. This study contributes to a deeper understanding of the structural dynamics in multivalent cathode materials and sets the stage for the development of advanced Mg-ion cathodes with enhanced performance and stability.

Interplanar Ferromagnetism Enhanced Ultrawide Zero Thermal Expansion in Kagome Cubic Intermetallic (Zr,Nb)Fe2.

A cubic metal exhibiting zero thermal expansion (ZTE) over a wide temperature window demonstrates significant applications in a broad range of advanced technologies but is extremely rare in nature. Here, enabled by high-temperature synthesis, we realize tunable thermal expansion via magnetic doping in the class of kagome cubic (Fd-3m) intermetallic (Zr,Nb)Fe2. A remarkably isotropic ZTE is achieved with a negligible coefficient of thermal expansion (+0.47 × 10-6 K-1) from 4 to 425 K, almost wider than most ZTE in metals available. A combined in situ magnetization, neutron powder diffraction, and hyperfine Mössbauer spectrum analysis reveals that interplanar ferromagnetic ordering contributes to a large magnetic compensation for normal lattice contraction upon cooling. Trace Fe-doping introduces extra magnetic exchange interactions that distinctly enhance the ferromagnetism and magnetic ordering temperature, thus engendering such an ultrawide ZTE. This work presents a promising ZTE in kagome metallic materials.

IrGe4: A Predicted Weyl-Metal with a Chiral Crystal Structure.

Polycrystalline IrGe4 was synthesized by annealing elements at 800 °C for 240 h, and the composition was confirmed by energy-dispersive X-ray spectroscopy. IrGe4 adopts a chiral crystal structure (space group P3121) instead of a polar crystal structure (P31), which was corroborated by the convergent-beam electron diffraction and Rietveld refinements using synchrotron powder X-ray diffraction data. The crystal structure features layers of IrGe8 polyhedra along the b axis, and the layers are connected by edge- and corner-sharing. Each layer consists of corner-shared [Ir3Ge20] trimers, which are formed by three IrGe8 polyhedra connected by edge-sharing. Temperature-dependent resistivity indicates metallic behavior. The magnetoresistance increases with increasing applied magnetic field, and the nonsaturating magnetoresistance reaches 11.5% at 9 T and 10 K. The Hall resistivity suggests that holes are the majority carrier type, with a carrier concentration of 4.02 × 1021 cm-3 at 300 K. Electronic band structures calculated by density functional theory reveal a Weyl point with a chiral charge of +3 above the Fermi level.

Investigation of Ca Insertion into α-MoO3 Nanoparticles for High Capacity Ca-Ion Cathodes.

Calcium-ion batteries (CIBs) are a promising alternative to lithium-ion batteries (LIBs) due to the low redox potential of calcium metal and high abundance of calcium compounds. Due to its layered structure, α-MoO3 is regarded as a promising cathode host lattice. While studies have reported that α-MoO3 can reversibly intercalate Ca ions, limited electrochemical activity has been noted, and its reaction mechanism remains unclear. Here, we re-examine Ca insertion into α-MoO3 nanoparticles with a goal to improve reaction kinetics and clarify the storage mechanism. The α-MoO3 electrodes demonstrated a specific capacity of 165 mA h g-1 centered near 2.7 V vs Ca2+/Ca, stable long-term cycling, and good rate performance at room temperature. This work demonstrates that, under the correct conditions, layered oxides can be a promising host material for CIBs and renews prospects for CIBs.

Unconventional Charge Transport in MgCr2O4 and Implications for Battery Intercalation Hosts.

Ion transport in solid-state cathode materials prescribes a fundamental limit to the rates batteries can operate; therefore, an accurate understanding of ion transport is a critical missing piece to enable new battery technologies, such as magnesium batteries. Based on our conventional understanding of lithium-ion materials, MgCr2O4 is a promising magnesium-ion cathode material given its high capacity, high voltage against an Mg anode, and acceptable computed diffusion barriers. Electrochemical examinations of MgCr2O4, however, reveal significant energetic limitations. Motivated by these disparate observations; herein, we examine long-range ion transport by electrically polarizing dense pellets of MgCr2O4. Our conventional understanding of ion transport in battery cathode materials, e.g., Nernst-Einstein conduction, cannot explain the measured response since it neglects frictional interactions between mobile species and their nonideal free energies. We propose an extended theory that incorporates these interactions and reduces to the Nernst-Einstein conduction under dilute conditions. This theory describes the measured response, and we report the first study of long-range ion transport behavior in MgCr2O4. We conclusively show that the Mg chemical diffusivity is comparable to lithium-ion electrode materials, whereas the total conductivity is rate-limiting. Given these differences, energy storage in MgCr2O4 is limited by particle-scale voltage drops, unlike lithium-ion particles that are limited by concentration gradients. Future materials design efforts should consider the interspecies interactions described in this extended theory, particularly with respect to multivalent-ion systems and their resultant effects on continuum transport properties.

Evolution of Bonding and Magnetism via Changes in Valence Electron Count in CuFe2-xCoxGe2.

A series of solid solutions, CuFe2-xCoxGe2 (x = 0, 0.2, 0.4, 0.8, and 1.0), have been synthesized by arc-melting and characterized by powder X-ray and neutron diffraction, magnetic measurements, Mössbauer spectroscopy, and electronic band structure calculations. All compounds crystallize in the CuFe2Ge2 structure type, which can be considered as a three-dimensional framework built of fused MGe6 octahedra and MGe5 trigonal bipyramids (M = Fe and Co), with channels filled by rows of Cu atoms. As the Co content (x) increases, the unit cell volume decreases in an anisotropic fashion: the b and c lattice parameters decrease while the a parameter increases. The changes in all the parameters are nearly linear, thus following Vegard's law. CuFe2Ge2 exhibits two successive antiferromagnetic (AFM) orderings, corresponding to the formation of a commensurate AFM structure, followed by an incommensurate AFM structure observed at lower temperatures. As the Co content increases, the AFM ordering temperature (TN) gradually decreases, and only one AFM transition is observed for x ≥ 0.2. The magnetic behavior of unsubstituted CuFe2Ge2 was found to be sensitive to the preparation method. The temperature-dependent zero-field 57Fe Mössbauer spectra reveal two hyperfine split components that evolve in agreement with the two consecutive AFM orderings observed in magnetic measurements. In contrast, the field-dependent spectra obtained for fields ≥2 T reveal a parallel arrangement of the moments associated with the two crystallographically unique metal sites. Electronic band structure calculations and chemical bonding analysis reveal a mix of strong M-M antibonding and non-bonding states at the Fermi level, in support of the overall AFM ordering observed in zero field. The substitution of Co for Fe reduces the population of the M-M antibonding states and the overall density of states at the Fermi level, thus suppressing the TN value.

Operando X-ray Diffraction Studies of the Mg-Ion Migration Mechanisms in Spinel Cathodes for Rechargeable Mg-Ion Batteries.

A promising high-voltage spinel oxide cathode material MgCrMnO4 with 18% Mg/Mn inversion was synthesized successfully. A new custom operando battery device was designed to study the cation migration mechanisms of the MgCrMnO4 cathode using 0.1 M Mg(TPFA)2 electrolyte dissolved in triglyme and activated carbon as the anode. For the first time in multivalent batteries, high-quality operando diffraction data enabled the accurate quantification of cation contents in the host structure. Besides the exceptional reversibility of 12% Mg2+ insertion in Mg1-xCrMnO4 (x ≤ 1), a partially reversible insertion of excess Mg2+ during overdischarging was also observed. Moreover, the insertion/extraction reaction was experimentally shown to be accompanied by a series of cation redistributions in the spinel framework, which were further supported by density functional theory calculations. The inverted Mn is believed to be directly involved in the cation migrations, which would cause voltage hysteresis and irreversible structural evolution after overdischarging. Tuning the Mg/Mn inversion rate could provide a direct path to further optimize spinel oxide cathodes for Mg-ion batteries, and more generally, the operando techniques developed in this work should play a key role in understanding the complex mechanisms involved in multivalent ion insertion systems.

Tl2Ir2O7: A Pauli Paramagnetic Metal, Proximal to a Metal Insulator Transition.

A polycrystalline sample of Tl2Ir2O7 was synthesized by high-pressure and high-temperature methods. Tl2Ir2O7 crystallizes in the cubic pyrochlore structure with space group Fd3̅m (No. 227). The Ir4+ oxidation state is confirmed by Ir-L3 X-ray absorption near-edge spectroscopy. Combined temperature-dependent magnetic susceptibility, resistivity, specific heat, and DFT+DMFT calculation data show that Tl2Ir2O7 is a Pauli paramagnetic metal, but it is close to a metal-insulator transition. The effective ionic size of Tl3+ is much smaller than that of Pr3+ in metallic Pr2Ir2O7; hence, Tl2Ir2O7 would be expected to be insulating according to the established phase diagram of the pyrochlore iridate compounds, A3+2Ir4+2O7. Our experimental and theoretical studies indicate that Tl2Ir2O7 is uniquely different from the current A3+2Ir4+2O7 phase diagram. This uniqueness is attributed primarily to the electronic configuration difference between Tl3+ and rare-earth ions, which plays a substantial role in determining the Ir-O-Ir bond angle, and the corresponding electrical and magnetic properties.

High-Pressure Synthesis of Double Perovskite Ba2NiIrO6: In Search of a Ferromagnetic Insulator.

Double perovskite oxides with d8-d3 electronic configurations are expected to be ferromagnetic from the Goodenough-Kanamori rules, such as ferromagnetic La2NiMnO6. In search of new ferromagnetic insulators, double perovskite Ba2NiIrO6 was successfully synthesized by high-pressure and high-temperature methods (8 GPa and 1573 K). Ba2NiIrO6 crystallizes in a cubic double perovskite structure (space group: Fm3̅m), with an ordered arrangement of NiO6 and IrO6 octahedra. X-ray absorption near-edge spectroscopy confirms the nominal Ni(II) and Ir(VI) valence states. Ba2NiIrO6 displays an antiferromagnetic order at 51 K. The positive Weiss temperature, however, indicates that ferromagnetic interactions are dominant. Isothermal magnetization curves at low temperatures support a field-induced spin-flop transition.

Iridate Li8IrO6: An Antiferromagnetic Insulator.

A polycrystalline iridate Li8IrO6 material was prepared via heating Li2O and IrO2 starting materials in a sealed quartz tube at 650 °C for 48 h. The structure was determined from Rietveld refinement of room-temperature powder neutron diffraction data. Li8IrO6 adopts the nonpolar space group R3̅ with Li atoms occupying the tetrahedral and octahedral sites, which is supported by the electron diffraction and solid-state 7Li NMR. This results in a crystal structure consisting of LiO4 tetrahedral layers alternating with mixed IrO6 and LiO6 octahedral layers along the crystallographic c-axis. The +4 oxidation state of Ir4+ was confirmed by near-edge X-ray absorption spectroscopy. An in situ synchrotron X-ray diffraction study of Li8IrO6 indicates that the sample is stable up to 1000 °C and exhibits no structural transitions. Magnetic measurements suggest long-range antiferromagnetic ordering with a Néel temperature (TN) of 4 K, which is corroborated by heat capacity measurements. The localized effective moment µeff (Ir) = 1.73 µB and insulating character indicate that Li8IrO6 is a correlated insulator. First-principles calculations support the nonpolar crystal structure and reveal the insulating behavior both in paramagnetic and antiferromagnetic states.

Ferrimagnetic Ordering and Anomalous Stoichiometry Observed for the Cubic, Extended 3D Prussian Blue Analogues (NEt3 Me)2 MnII 5 (CN)12 and (NEt2 Me2 )2 MnII 5 (CN)12 : A Cation-Adaptive Structure.

The reactions of MnII (O2 CCH3 )2 with NEt3 Me+ CN- and NEt2 Me2 + CN- form (NEt3 Me)2 MnII 5 (CN)12 (1) and (NEt2 Me2 )2 MnII 5 (CN)12 (2), respectively. Structure model-building and Rietveld refinement of high-resolution synchrotron powder diffraction data revealed a cubic [a=24.0093 Š(1), 23.8804 Š(2)] 3D extended structural motif with adjacent tetrahedral and octahedral MnII sites in a 3:2 ratio. Each tetrahedral MnII site is surrounded by four low-spin octahedral MnII sites, and each octahedral MnII site is surrounded by six high-spin tetrahedral MnII sites; adjacent sites are antiferromagnetically coupled in 3D. Compensation does not occur, and magnetic ordering as a ferrimagnet is observed at Tc =13 K for 2 based on the temperature at which remnant magnetization, Mr (T)→0. The hysteresis has an unusual constricted shape with inflection points around 50 and 1.2 kOe with a 5 K coercivity of 16 Oe and remnant magnetization, Mr , of 2050 emuOe mol-1 . The unusual structure and stoichiometry are attributed to the very ionic nature of the high-spin N-bonded MnII ion, which enables the maximization of the attractive van der Waals interactions through minimization of void space via a reduced ∠ MnNC. This results in an additional example of the Ax MnII y (CN)x+2y (x=0, y=1; x=1, y=3; x=2, y=1; x=2, y=2; x=2, y=3; x=3, y=5; and x=4, y=1) family of compounds possessing an unprecedented stoichiometry and lattice motif that are cation adaptive structured materials.

Synthesis of Antiperovskite Solid Electrolytes: Comparing Li3SI, Na3SI, and Ag3SI.

Prior calculations have predicted that chalcohalide antiperovskites may exhibit enhanced ionic mobility compared to oxyhalide antiperovskites as solid-state electrolytes. Here, the synthesis of Ag-, Li-, and Na-based chalcohalide antiperovskites is investigated using first-principles calculations and in situ synchrotron X-ray diffraction. These techniques demonstrate that the formation of Ag3SI is facilitated by the adoption of a common body centered cubic packing of S2- and I- in the reactants and products at elevated temperatures, with additional stabilization achieved by the formation of a solid solution of the anions. The absence of these two features appears to hinder the formation of the analogous Li and Na antiperovskites.

Structure and Negative Thermal Expansion in Zr0.3Sc1.7Mo2.7V0.3O12.

A2M3O12-based materials have received considerable attention owing to their wide range of negative thermal expansion (NTE) and chemical flexibility toward novel materials design. However, the structure and NTE mechanism remain challenging. Here, Zr4+ and V5+ are used as a unit to compensatorily replace Sc3+ and Mo6+ in Sc2Mo3O12 to tune its thermal expansion. Its crystal structure, phase transition, NTE property, and corresponding mechanisms are studied by high-resolution synchrotron X-ray diffraction, powder X-ray diffraction, ultralow-frequency Raman spectroscopy, and density functional theory calculations. The results show that Zr0.3Sc1.7Mo2.7V0.3O12 adopts an orthorhombic (Pbcn) structure at room temperature, with V atoms occupying the position of Mo1 atoms and Zr atoms occupying the position of Sc atoms, and transforms to monoclinic (P21/a) structure at ∼133 K (45 K lower than that of Sc2Mo3O12). It exhibits excellent NTE in a broader range. Most of the phonon modes below 350 cm-1 have negative Grüneisen parameters, of which the lowest and next-lowest frequency (38.5 and 45.8 cm-1) optical phonon modes arising from the translational vibrations of the Sc/Zr and Mo/V atoms in the plane of the nonlinear linkage Sc/Zr-O-Mo/V have the largest and next-largest negative Grüneisen parameters and positive total anharmonicity, and contribute most to the NTE.

Synthesis, Crystal Structure, and Cooperative 3d-5d Magnetism in Rock Salt Type Li4NiOsO6 and Li3Ni2OsO6.

Two new transition metal oxides with the nominal chemical compositions of Li4NiOsO6 and Li3Ni2OsO6 were successfully synthesized. Both compounds crystallize in an ordered rock salt structure type in the monoclinic C2/m space group. The crystal structures were determined using both synchrotron X-ray and time-of-flight neutron, powder diffraction data. In both phases, Ni2+ ions are present while oxidation states of osmium are +6 and +5 in Li4NiOsO6 and Li3Ni2OsO6, respectively. Ni2+ ions in the hypothetical fully ordered phase form a honeycomb arrangement in the ab crystallographic plane and these hexagons are centered by osmium ions. The magnetic layers are separated along the c axis by the octahedra, which are centered by Li+ (or Li+/Ni2+, depending on the chemical compositions). Crystal structure refinements reveal that there is some degree of mixed occupancy in cationic positions. Temperature dependent magnetic susceptibility data for both phases show ferrimagnetic transitions with predominant antiferromagnetic (AFM) interactions among 3d electrons of nickel and 5d electrons of osmium. Iso-thermal magnetization loops as a function of the applied magnetic field below the transition temperatures confirm the ferrimagnetic nature in magnetic transitions. Temperature dependent heat capacity data, however, did not exhibit any anomaly in either phase, indicating the absence of long-range magnetic ordering. The lack of long-range order for both Os5+ and Os6+-based compounds was also confirmed by low temperature neutron diffraction data down to 10 K. Temperature dependent AC magnetic susceptibility data in various frequencies for both samples indicate that Li4NiOsO6 exhibits spin-glass-like behavior, while the transition temperature for Li3Ni2OsO6 is nearly frequency independent.

Single-Crystal Growth and Room-Temperature Magnetocaloric Effect of X-Type Hexaferrite Sr2Co2Fe28O46.

X-type hexaferrites have been receiving considerable attention due to their promising applications in many magnetic-electronic fields. However, the growth of single-crystal X-type hexaferrite is still a challenge. Herein we reported, for the first time, the preparation of single crystal X-type hexaferrite Sr2Co2Fe28O46 (Sr2Co2X) with high-quality and large size using floating-zone method with laser as the heating source. The crystals show rhombohedral symmetry with space group of R-3m (No. 166, a = 5.8935(1) Å and c = 83.7438(17) Å). Co2+ and Fe3+ oxidation states were confirmed by the X-ray absorption near-edge spectroscopy. The prepared Sr2Co2X exhibits a spin reorientation transition from easy-cone to easy-axis at T2 of 343 K and a ferrimagnetism-paramagnetism transition at Curie temperature (TC) of ∼743 K. The spin reorientation transition was accompanied by magnetocaloric effect (MCE). Both conventional and inverse MCEs were observed near T2 with a magnetic field applied along the c-axis. The maximum value of the magnetic entropy change along the c-axis was evaluated to be 1.1 J/kg·K for a magnetic field change of 5 T.

High-Pressure, High-Temperature Synthesis and Characterization of Polar and Magnetic LuCrWO6.

A new polar and magnetic oxide, LuCrWO6, was synthesized under high pressure (6 GPa) and high temperature (1673 K). LuCrWO6 is isostructural with the previously reported polar YCrWO6 (SG: Pna21, no. 33). The ordering of CrO6 and WO6 octahedra in the edge-shared dimers induce the polar structure. The effective size of rare earth, Ln cation does not seem to affect the symmetry of LnCrWO6. Second harmonic generation measurements of LuCrWO6 confirmed the noncentrosymmetric character and strong piezoelectric domains are observed from piezoresponse force microscopy at room temperature. LuCrWO6 exhibits antiferromagnetic behavior, TN, of ∼18 K with a Weiss temperature of -30.7 K.

Ambient and High Pressure CuNiSb2: Metal-Ordered and Metal-Disordered NiAs-Type Derivative Pnictides.

The mineral Zlatogorite, CuNiSb2, was synthesized in the laboratory for the first time by annealing elements at ambient pressure (CuNiSb2-AP). Rietveld refinement of synchrotron powder X-ray diffraction data indicates that CuNiSb2-AP crystallizes in the NiAs-derived structure (P3m1, #164) with Cu and Ni ordering. The structure consists of alternate NiSb6 and CuSb6 octahedral layers via face-sharing. The formation of such structure instead of metal disordered NiAs-type structure (P63/mmc, #194) is validated by the lower energy of the ordered phase by first-principle calculations. Interatomic crystal orbital Hamilton population, electron localization function, and charge density analysis reveal strong Ni-Sb, Cu-Sb, and Cu-Ni bonding and long weak Sb-Sb interactions in CuNiSb2-AP. The magnetic measurement indicates that CuNiSb2-AP is Pauli paramagnetic. First-principle calculations and experimental electrical resistivity measurements reveal that CuNiSb2-AP is a metal. The low Seebeck coefficient and large thermal conductivity suggest that CuNiSb2 is not a potential thermoelectric material. Single crystals were grown by chemical vapor transport. The high pressure sample (CuNiSb2-8 GPa) was prepared by pressing CuNiSb2-AP at 700 °C and 8 GPa. However, the structures of single crystal and CuNiSb2-8 GPa are best fit with a disordered metal structure in the P3m1 space group, corroborated by transmission electron microscopy.

In situ investigation of phosphonate retarder interaction in oil well cements at elevated temperature and pressure conditions.

The effect of a high-performance retarding additive in oil well cements was investigated under elevated temperature (165°C) and pressure (1000 psi) conditions via in situ synchrotron-based X-ray diffraction (XRD) and quasielastic neutron scattering (QENS) techniques. Under these temperature and pressure conditions, crystalline calcium silicate hydrates (C-S-H) are formed through the cement hydration process. From in situ XRD experiments, the retardation effect was observed by a change in the rate of the appearance of 11 Å tobermorites as well as a change in the rate of the α-C2SH generation and depletion. QENS analysis revealed that the retardation effect was related to the non-conversion of free water to chemical and constrained water components. A high presence of free water components was attributed to a decrease in 11 Å tobermorites along with slower consumption of the quartz and portlandite phases. Furthermore, QENS results infer that the water molecules experienced confinement in the restricted pore spaces. The retarder inhibited this initial water confinement by slowing the bulk diffusion of free water in the confined region.