X-ray Pair Research Articles

Pyrochlore NaYbO2: A Potential Quantum Spin Liquid Candidate.

The search for quantum spin liquids (QSL) and chemical doping in such materials to explore superconductivity have continuously attracted intense interest. Here, we report the discovery of a potential QSL candidate, pyrochlore-lattice β-NaYbO2. Colorless and transparent NaYbO2 single crystals, layered α-NaYbO2 (∼250 μm on edge) and octahedral β-NaYbO2 (∼50 μm on edge), were grown for the first time. Synchrotron X-ray single-crystal diffraction unambiguously determined that the newfound β-NaYbO2 belongs to the three-dimensional pyrochlore structure characterized by the R3̅m space group, corroborated by synchrotron X-ray and neutron powder diffraction and pair distribution function. Magnetic measurements revealed no long-range magnetic order or spin glass behavior down to 0.4 K with a low boundary spin frustration factor of 17.5, suggesting a potential QSL ground state. Under high magnetic fields, the potential QSL state was broken and spins order. Our findings reveal that NaYbO2 is a fertile playground for studying novel quantum states.

Reinvestigating atomic ordering in K0.5Na0.5NbO3 and its impact on ferroelectric properties

In the present work, we reinvestigate the atomic ordering of a Pb-free morphotropic phase boundary (MPB) compositionviz.,K0.5Na0.5NbO3(KNN50) and its vicinity at various length scales using high-resolution x-ray diffraction and pair distribution function data. We have observed a monoclinic phase (Space Group: Pm) at long/short ranges differing from a very recent report by Sahaet al2024J. Phys.: Condens. Matter36425703. Moreover, the ferroelectric (polarization) dominance of short-range ordering (SRO) over long-range ordering (LRO) has been observed and quantified for the very first time using the amplitude of the ferroelectric frozen phonon mode (Γ4-) (corresponding to the high symmetry cubic phase), thereby structure is linked with ferroelectric (or polarization) property for a widely studied MPB systemviz.,KxNa(1-x)NbO3(KNNxforx= 0.40, 0.50, and 0.60). Two uniquely identified monoclinic phases has been observed for SRO (MSRO) and LRO (MLRO) for all the compositions. The amplitude of ferroelectric frozen phonon mode (Γ4-) corresponding toMSROis significantly higher (≈150%-180%) thanMLRO. A peak is observed in the amplitude ofΓ4-and intensity of prominent Raman peaks (ν1andν5) forx= 0.50, which is held responsible for high physical propertiesviz.,dielectric permittivity, piezoelectric coefficient, remnant polarization, electromechanical coupling coefficient, and many more widely reported in literature for KNN50.

The Structure of Glassy and Liquid Sulfur Revisited

High energy x-ray experiments have been performed on liquid and glassy sulfur over a wide temperature range. Heating the elastic quenched glass above -9 ºC and supercooling liquid sulfur below 51 ºC both resulted in crystallization to monoclinic sulfur. The average coordination number of the first shell in glassy sulfur determined from the pair distribution function is found to be 1.90±0.05. This result is in good agreement with previous neutron and x-ray pair distribution function studies, and lends support to the recent proposal that there are a significant number of short chains in the low temperature liquid upon melting. Also, a non-negligible coordination number of 0.20±0.04 is found in the interstitial region between the first and second shells in glassy sulfur, similar to that found in the liquid. An increase in the third peak in the glassy pair distribution function at 4.47 Å associated with S8-rings indicates the percentage is higher in the quenched glass compared to the stable liquid. This casts doubt on previous estimations of the percentage of S8-rings present upon melting.

S-d Coupling-Induced Dynamic Off-Centering of Cu Drives High Thermoelectric Performance in TlCuS.

Seeking new and efficient thermoelectric materials requires a detailed comprehension of chemical bonding and structure in solids at microscopic levels, which dictates their intriguing physical and chemical properties. Herein, we investigate the influence of local structural distortion on the thermoelectric properties of TlCuS, a layered metal sulfide featuring edge-shared Cu-S tetrahedra within Cu2S2 layers. While powder X-ray diffraction suggests average crystallographic symmetry with no distortion in CuS4 tetrahedra, the synchrotron X-ray pair distribution function experiment exposes concealed local symmetry breaking, with dynamic off-centering distortions of the CuS4 tetrahedra. The Cu off-centering is driven by the on-site coupling of filled 3d and unoccupied 4s orbitals (s-d) of Cu through a second-order Jahn-Teller mechanism. Bond softening by the p-d* (S-3p and Cu-3d) antibonding interaction coupled with dynamic off-centering distortions causes significant anharmonicity in the lattice, which acts as a phonon-blocking mechanism conducive to ultralow lattice thermal conductivity (κlat) (∼0.35-0.23 W m-1 K-1 in the ∼296-573 K temperature range) in TlCuS. The synergy between low κlat and multiband electronic structure leads to thermoelectric figure-of-merits (zT) of ∼1 and ∼1.3 at 573 K for pristine TlCuS and TlCu0.98S, respectively, underscoring the potential of metal sulfides as promising high-performance thermoelectrics.

Photocatalytic Dehalogenation of Aryl Halides Mediated by the Flexible Metal-Organic Framework MIL-53(Cr).

The catalytic potential of flexible metal-organic frameworks (MOFs) remains underexplored, particularly in liquid-phase reactions. This study employs MIL-53(Cr), a prototypical "breathing" MOF capable of structural adaptation via pore size modulation, as a photocatalyst for the dehalogenation of aryl halides. Powder X-ray diffraction and Pair Distribution Function analyses reveal that organic solvents influence pore opening, while substrates and products dynamically adjust the framework configuration during catalysis. This structural flexibility enables precise tuning of photocatalytic efficiency via solvent-mediated control of the pore aperture. The results demonstrate that the dynamic behavior of MIL-53(Cr) facilitates enhanced catalytic activity and selectivity, advancing the application of flexible MOFs as tunable, enzyme-mimicking catalysts. These findings pave the way for the rational design of next-generation flexible photocatalysts.

(Invited) Lithium Ion Conduction by Molecular Vibrations in Ion-Conducting Glasses

Controlling Li ion conduction in glasses at atomic and molecular levels is key to realizing all-solid-state batteries, a promising technology for electric vehicles. In this context, Li3PS4 glass, a promising solid electrolyte candidate, exhibits dynamic coupling between the Li+ cation mobility and the PS4 3− anion libration, which is commonly referred to as the paddlewheel effect1. In addition, it exhibits a concerted cation diffusion effect (i.e., a cation–cation interaction), which is regarded as the essence of high Li ion conduction. However, the correlation between the Li+ ions within the glass structure can only be vaguely determined, due to the limited experimental information. We report that the Li ions present in glasses can be classified by evaluating their valence oscillations via Bader analysis to topologically analyse the chemical bonds2. We found that three types of Li ions are present in Li3PS4 glass, and that the more mobile Li ions exhibit a characteristic correlation at relatively long distances of 4.0–5.0 Å. Furthermore, reverse Monte Carlo simulations combined with deep learning potentials that reproduce X-ray, neutron, and electron diffraction pair distribution functions showed an increase in the number of more mobile Li ions for partially crystallised glass structures with improved Li ion conduction properties. Our results show order within the disorder of the Li ion distribution in the glass by a topological analysis of their valences. References J. G. Smith, D. J. Siegel, Nature Communications, 11 (1), 1483 (2020). H. Yamada, K. Ohara, S. Hiroi, A. Sakuda, K. Ikeda, T. Ohkubo, K. Nakada, H. Tsukasaki, H. Nakajima, L. Temleitner, L. Pusztai, S. Ariga, A. Matsuo, J. Ding, T. Nakano, T. Kimura, R. Kobayashi, T. Usuki, S. Tahara, K. Amezawa, Y. Tateyama, S. Mori, and A. Hayashi, Energy & Environmental Materials, e12612 (2023).

Structural Disorder of a Layered Lithium Manganese Oxide Cathode Paving a Reversible Phase Transition Route toward Its Theoretical Capacity.

Layered lithium manganese oxides suffer from irreversible phase transitions induced by Mn migration and/or dissolution associated with the Jahn-Teller effect (JTE) of Mn3+, leading to inevitable capacity fading during cycling. The popular doping strategy of oxidizing Mn3+ to Mn4+ to relieve the JTE cannot completely eliminate the detrimental structural collapse from the cooperative JTE. Therefore, they are considered to be impractical for commercial use as cathode materials. Here, we demonstrate a layered lithium manganese oxide that can be charged and discharged without any serious structural collapse using metastable Li-birnessite with controlled structural disorder. Although Li-birnessite is thermodynamically unstable under ambient conditions, Li ion exchange into Na-birnessite followed by an optimal dehydration resulted in a disordered Li-birnessite. The control over crystal water in the interlayer provides intriguing short-range order therein, which can help to suppress parasitic Mn migration and dissolution, thereby ensuring a reversible electrochemical cycling. The Mn redox behavior and local structure change of the Li-birnessite were investigated by ex situ soft X-ray absorption spectroscopy (sXAS) and X-ray pair distribution function (PDF) analysis. The combined sXAS and PDF with electrochemical analyses disclosed that the reversible Mn redox and suppressed phase transitions in Dh Li-birnessite contribute to dramatically improving its electrochemical reversiblity during cycling. Our findings underscore the substantial effects of controlled static disorder on the structural stability and electrochemical reversibility of a layered lithium manganese oxide, Li-birnessite, which extends the practical capacity of layered oxides close to their theoretical limit.

Intrinsic oxygen evolution reaction activity and stability enhancement of IrOx electrocatalysts by microwave irradiation

Intrinsic oxygen evolution reaction activity and stability enhancement of IrOx electrocatalysts by microwave irradiation

Tailoring Atomic Ordering Uniformity Enables Selectively Leached Nanoporous Pd-Ni-P Metallic Glass for Enhanced Glucose Sensing.

Constructing nanostructures, such as nanopores, within metallic glasses (MGs) holds great promise for further unlocking their electrochemical capabilities. However, the MGs typically exhibit intrinsic atomic-scale isotropy, posing a significant challenge in directly fabricating anisotropic nanostructures using conventional chemical synthesis. Herein a selective leaching approach, which focuses on tailoring the uniformity of atomic ordering, is introduced to achieve pore-engineered Pd-Ni-P MG. This innovative approach significantly boosts the number of exposed active sites, thereby enhancing the electrochemical sensitivity for glucose detection. Electrochemical tests reveal that the nanoporous Pd-Ni-P MG exhibits high sensitivity (3.19mA mm⁻¹ cm⁻2) and remarkable stability (97.7% current retention after 1000 cycles). During electrochemical cycling, synchrotron X-ray pair distribution function and X-ray absorption fine structure analyses reveal that the distance between active sites decreases, enhancing electron transport efficiency, while the medium-range ordered structure of the Pd-Ni-P MG remains stable, contributing to its exceptional glucose sensing capabilities. A microglucose sensor is successfully developed by integrating the nanoporous Pd-Ni-P MG with a screen-printed electrode, demonstrating the practical applicability. This study not only offers a new avenue for the design of highly active nanoporous MGs but also sheds light on the mechanisms behind the high electrochemistry performance of MGs.

Impacts of distorted local chemical coordination on electrochemical performance in hydrated vanadium pentoxide

Modulating and elevating the operating voltage of a given cathode is a significant challenge to enhance the energy density of secondary batteries without sacrificing power output. The chemical coordination strongly influences the energy levels of d-orbitals of redox cations in cathode materials, which tie to their operating voltage. In contrast to concentrated studies on enhancing the specific capacity, in this study, we choose bi-layered hydrated vanadium pentoxide as the model to modulate the d-orbital energy levels through local chemical coordination manipulation, achieving a higher operating voltage in rechargeable aqueous zinc ion batteries. Here we show that, by employing X-ray absorption spectroscopy (XAS) and pair distribution function (PDF) techniques, we can analyze the distortion of [VO6] octahedra and extract chemical bond information, deciphering the correlation between the chemical coordination and operating voltage in cathode materials. The fundamentals could guide the designing and developing RAZIBs with higher energy and power density.

Influence of Subvalent Twin-Rattler for High n-Type Thermoelectric Performance in Bi13S18Br2 Chalcohalide.

Metal chalcohalides, owing to their higher stability over halides and greater tunability of electronic features over chalcogenides, open new avenues for investigating properties of materials. Complex metal chalcohalides can be a good choice for thermoelectric studies for their halide-like low thermal conductivity and chalcogenide-like high electrical conductivity. Here, we have investigated the thermoelectric properties of n-type Bi13S18Br2 and utilized the concept of Fajans' polarization to describe the formation of a dimer and explained how it can help achieve high thermoelectric figure of merit (zT) of ∼1.0 at 748 K. This zT value is so far the highest-reported value for pristine metal chalcohalides. The existence of subunit in Bi13S18Br2 is experimentally verified by synchrotron X-ray pair distribution function (X-PDF) analysis. The complex structure of Bi13S18Br2 having a large unit cell exhibits simultaneous dimer-cation rattler (i.e., "twin-rattler"), which decreases the lattice thermal conductivity drastically. We observed evidence of such low-energy rattling vibrations from DFT-calculated eigen mode visualizations of the phonon dispersion. The subvalent nature of accommodates an extra electron in Bi(6pz) orbital, which helps form a weakly dispersed donor band just below the Fermi energy (EF), leading to a significant reduction in band gap (0.77 eV), which is favorable for high thermoelectric performance. Consequently, we obtained a semiconducting nature of n-type Bi13S18Br2 with moderate electrical conductivity, as well as a high Seebeck coefficient. Our investigation presents the importance of fundamental chemistry in thermoelectrics and demonstrates the influence of subvalent twin-rattler in triggering high thermoelectric performance in metal chalcohalides.

Evidence of short chains in liquid sulfur.

High energy x-ray pair distribution function measurements show the average coordination number of the first shell in liquid sulfur is 1.86 ± 0.04 across the λ-transition, not precisely 2.0 as widely accepted. This indicates that upon melting, liquid sulfur does not comprise solely of S8 rings but also possesses a significant number of short chains. Intensities of the pre-peak and first diffraction peak of the x-ray structure factor and third peak height of the pair distribution function all show deviations at the λ-transition temperature Tλ, associated with the break-up of S8 rings and the start of oligomer polymerization. A significant number of non-bonded or loosely bonded "interstitial atoms," with an average coordination number of 0.20 ± 0.005, are also observed in the so-called "forbidden zone" between the first and second shells upon melting. The number of interstitial atoms is found to decrease to a minimum at the λ-transition, but the majority persist into the high temperature polymerized liquid. The existence of short chains and nearby interstitial atoms represent the two main factors required to initiate the S8-ring to chain transition, as proposed by recent molecular dynamics simulations.

Selective single-atom adsorption for precision separation of lead ions in tap water via capacitive deionization

Capacitive deionization (CDI) offers a cost-effective and low-energy method for selective removal of Pb2+ from drinking water. Modifying CDI electrode surfaces with functional groups presents a versatile approach to enhancing selective ion adsorption capacity. However, a comprehensive understanding of the selectivity and removal efficiency of Pb2+ among diverse functional groups remains unexplored. Here, we investigated the effects of different functional groups (-SH, -COOH, and -NH2) attached to the graphene oxide (GO) electrode surfaces on Pb2+ selectivity and removal efficiency. Surprisingly, GO-COOH demonstrated single-atom adsorption of Pb2+, displaying superior removal efficiency and selectivity compared with -SH and -NH2, although -SH possesses significant chelation capability for Pb2+. Both density functional theory (DFT) calculations and X-ray pair distribution function (PDF) analyses confirmed that Pb2+ exhibits a theoretically higher affinity to -COOH. This research deepens our understanding of the interactions between functional groups and heavy metal ions, enabling selective and rapid separation of target cations for water purification.

A strategy of consistent X-ray and neutron double-difference pair distribution function analysis of nanoparticle dispersions

AbstractIt has been demonstrated that the X-ray pair distribution function (PDF) formalism allows for the identification of very small signal contributions in multi-component systems by the difference and double-difference PDF (dd-PDF) approach. Due to their stronger interaction with light elements compared to X-rays, neutrons are often beneficial or complementary for the characterization of modern materials. Here, it is demonstrated that the dd-PDF strategy previously developed for X-ray PDF data can successfully be applied to neutron PDF data despite much lower count rates compared to X-rays. The dd-PDF strategy was employed for the investigation of aqueous iron oxide nanoparticle (IONP) dispersions. At the Near and InterMediate Range Order Diffractometer (NIMROD) at ISIS, the IONPs could even be investigated in pure water, whereas at the Nanoscale Ordered Materials Diffractometer (NOMAD) at SNS, heavy water had to be used, but additional information could be retrieved from modelling the data of IONP powder in the dry state and with adsorbed (heavy) water. The simple and robust approach can easily be adapted for the use in other multicomponent systems, like heterogenous catalysts or battery systems. Graphical Abstract

Energy-efficient synthesis of Ti3C2Tx MXene for electromagnetic shielding

Energy-efficient synthesis of Ti3C2Tx MXene for electromagnetic shielding

When van der Waals Met Kagome: A 2D Antimonide with a Vanadium-Kagome Network.

2D materials showcase unconventional properties emerging from quantum confinement effects. In this work, a "soft chemical" route allows for the deintercalation of K+ from the layered antimonide KV6Sb6, resulting in the discovery of a new metastable 2D-Kagome antimonide K0.1(1)V6Sb6 with a van der Waals gap of 3.2 Å. The structure of K0.1(1)V6Sb6 was determined via the synergistic techniques, including X-ray pair distribution function analysis, advanced transmission electron microscopy, and density functional theory calculations. The K0.1(1)V6Sb6 compound crystallizes in the monoclinic space group C2/m (a = 9.57(2) Å, b = 5.502(8) Å, c = 10.23(2) Å, β = 97.6(2)°, Z = 2). The [V6Sb6] layers in K0.1(1)V6Sb6 are retained upon deintercalation and closely resemble the layers in the parent compound, yet deintercalation results in a relative shift of the adjacent [V6Sb6] layers. The magnetic properties of the K0.1(1)V6Sb6 phase in the 2-300 K range are comparable to those of KV6Sb6 and another Kagome antimonide KV3Sb5, consistent with nearly temperature-independent paramagnetism. Electronic band structure calculation suggests a nontrivial band topology with flat bands and opening of band crossing afforded by deintercalation. Transport property measurements reveal a metallic nature for K0.1(1)V6Sb6 and a low thermal conductivity of 0.6 W K-1 m-1 at 300 K. Additionally, ion exchange in KV6Sb6 via a solvothermal route leads to a successful partial exchange of K+ with A+ (A = Na, Rb, and Cs). This study highlights the tunability of the layered structure of the KV6Sb6 compound, providing a rich playground for the realization of new 2D materials.

Deciphering Pauling's Third Rule: Uncovering Strong Anharmonicity and Exceptionally Low Thermal Conductivity in TlAgSe for Thermoelectrics.

The elucidation of chemical bonding, coupled with an exploration of the correlated dynamics of constituent atoms, is essential for unravelling the underlying mechanism responsible for low lattice thermal conductivity (κL) exhibited by a crystalline solid, which is essential for thermoelectrics and thermal barrier coatings. In this regard, Pauling's third empirical rule, which deals with the cationic repulsion due to proximity in the face or edge shared polyhedra in a crystal structure, can bring about the lattice instability required to suppress the κL. Here, we demonstrate the presence of such instability in a ternary selenide, TlAgSe, leading to a ultra-low κL of 0.17 W/m.K at 573 K. Our study reveals the instability arising from Ag-Ag repulsion within edge-shared AgSe4 tetrahedra through investigation of the local structure using synchrotron X-ray pair distribution function (PDF) analysis and supported by first-principles density functional theory calculations. We observe correlation between weakening in the Ag and the Tl-sublattice, providing direct experimental evidence of Pauling's third empirical rule. The correlated rattling of Ag and Tl induces a highly anharmonic lattice and low energy optical phonons, resulting in suppressed sound velocity and ultralow κL in TlAgSe. The electronic origin of soft and anharmonic lattice is the presence of filled antibonding states in the valence band near the Fermi level constructed by Ag(4d)-Se(4p) and Tl(6s)-Se(4p) interactions. This work demonstrates that the evidence of dynamic distortion in a crystal lattice is governed by the third empirical rule given by Pauling, which can act as a potential new strategy for diminishing κL in crystalline solids.

3D Lead-Organoselenide-Halide Perovskites and their Mixed-Chalcogenide and Mixed-Halide Alloys.

We incorporate Se into the 3D halide perovskite framework using the zwitterionic ligand: SeCYS (+NH3(CH2)2Se-), which occupies both the X- and A+ sites in the prototypical ABX3 perovskite. The new organoselenide-halide perovskites: (SeCYS)PbX2 (X=Cl, Br) expand upon the recently discovered organosulfide-halide perovskites. Single-crystal X-ray diffraction and pair distribution function analysis reveal the average structures of the organoselenide-halide perovskites, whereas the local lead coordination environments and their distributions were probed through solid-state 77Se and 207Pb NMR, complemented by theoretical simulations. Density functional theory calculations illustrate that the band structures of (SeCYS)PbX2 largely resemble those of their S analogs, with similar band dispersion patterns, yet with a considerable band gap decrease. Optical absorbance measurements indeed show band gaps of 2.07 and 1.86 eV for (SeCYS)PbX2 with X=Cl and Br, respectively. We further demonstrate routes to alloying the halides (Cl, Br) and chalcogenides (S, Se) continuously tuning the band gap from 1.86 to 2.31 eV-straddling the ideal range for tandem solar cells or visible-light photocatalysis. The comprehensive description of the average and local structures, and how they can fine-tune the band gap and potential trap states, respectively, establishes the foundation for understanding this new perovskite family, which combines solid-state and organo-main-group chemistry.

Unfolding the mysterious roles of GeTe/SnTe compositing within CuInTe2 thermoelectric alloy: Short-range and local chemical orders

Unfolding the mysterious roles of GeTe/SnTe compositing within CuInTe2 thermoelectric alloy: Short-range and local chemical orders

Ultralow Thermal Conductivity in Vacancy-Ordered Halide Perovskite Cs3Bi2Br9 with Strong Anharmonicity and Wave-Like Tunneling of Low-Energy Phonons.

Halide perovskites are of great interest due to their exceptional optical and optoelectronic properties. However, thermal conductivity of many halide perovskites remains unexplored. In this study, an ultralow lattice thermal conductivity κL (0.24W m-1 K-1 at 300 K) is reported and its weak temperature dependence (≈T-0.27) in an all-inorganic vacancy-ordered halide perovskite, Cs3Bi2Br9. The intrinsically ultralow κL can be attributed to the soft low-lying phonon modes with strong anharmonicity, which have been revealed by combining experimental heat capacity and Raman spectroscopy measurements, and first-principles calculations. It is shown that the highly anharmonic phonons originate from the Bi 6s2 lone pair expression with antibonding states of Bi 6s and Br 4p orbitals driven by the dynamic BiBr6 octahedral distortion. Theoretical calculations reveal that these low-energy phonons are mostly contributed by large Br motions induced dynamic distortion of BiBr6 octahedra and large Cs rattling motions, verified by the synchrotron X-ray pair distribution function analysis. In addition, the weak temperature dependence of κL can be traced to the wave-like tunneling of phonons, induced by the low-lying phonon modes. This work reveals the strong anharmonicity and wave-like tunneling of low-energy phonons for designing efficient vacancy-ordered halide perovskites with intrinsically low κL.