Lattice Coupling Research Articles

Iron Doping of 2D Nickel-Based Metal-Organic Frameworks Enhances the Lattice Heterogeneous Interface Coupling Effect for Improved Electrocatalytic Oxygen Evolution.

The coupling of lattice and heterostructure interfaces represents an effective strategy for disrupting the so-called scalar relationship and accelerating reactions involving multiple intermediates. In view of this, a lattice-heterostructure interfacial catalyst consisting of a crystalline Fe/Ni bimetallic MOF and amorphous Fe-MOF was designed in this paper for high-performance alkaline oxygen evolution reaction electrocatalysis. The strongly coupled lattice-heterostructure interface induces a unique synergistic effect that promotes electron transfer of the catalyst. The resulting catalyst exhibits exceptionally high catalytic activity for the oxygen evolution reaction in alkaline media, the Ni9Fe1-BDC-1@Fe-MOF coated on a glassy carbon electrode has an overpotential of 257 mV at a current density of 10 mA cm-2. Furthermore, this catalyst demonstrates a high electrochemical stability. These research results highlight the superiority of lattice-heterostructure interfaces in the development of advanced catalysts.

High-efficiency and broadband asymmetric spin-orbit interaction based on high-order composite phase modulation.

Asymmetric spin-orbit interaction (ASOI) breaks the limitations in conjugate symmetry of traditional geometric phase metasurfaces, bringing new opportunities for various applications such as spin-decoupled holography, imaging, and complex light field manipulation. Since anisotropy is a requirement for spin-orbit interactions, existing ASOI mainly relies on meta-atom with C1 and C2 symmetries, which usually suffer from an efficiency decrease caused by the propagation phase control through the structural size. Here, we demonstrate for the first time that ASOI can be realized in meta-atoms with rotational symmetry ≥3 by combining the generalized geometric phase with the propagation phase. Utilizing an all-metallic configuration, the average diffraction efficiency of the spin-decoupled beam deflector based on C3 meta-atoms reaches ∼84 % in the wavelength range of 9.3-10.6 μm, which is much higher than that of the commonly used C2 meta-atoms with the same period and height. This is because the anisotropy of the C3 metasurface originates from the lattice coupling effect, which is relatively insensitive to the propagation phase control through the meta-atom size. A spin-decoupled beam deflector and hologram meta-device were experimentally demonstrated and performed well over a broadband wavelength range. This work opens a new route for ASOI, which is significant for realizing high-efficiency and broadband spin-decoupled meta-devices.

A complex magnetic study: evidence of spin-glass transition below long-range magnetic ordering and its correlation with renormalization of phonon modes

In this paper, we report a complex magnetic behavior arising due to the interplay of three active magnetic cations (Nd/Sm, Co and Ir), forming 3d-5d-4f magnetic sublattices. The B-site ordered double perovskites Nd2CoIrO6and Sm2CoIrO6were successfully prepared by conventional solid-state method. Detailed structural analysis revealed that both samples crystallized in monoclinic structure with P21/n (No.-14) space group. X-ray photoelectron spectroscopy analysis confirms the presence of multiple oxidation states of Ir (i.e. Ir4+and Ir5+). Both samples show a paramagnetic-ferrimagnetic (TFiM) transition around 100 K, additionally, a low temperature transition is observed at around 10 K in the SCIO sample. This FM-like behavior of the samples is attributed to the antiparallel alignment of the Co2+and Ir4+spins, resulting in FiM ordering. The ac susceptibility analysis confirms a spin glass type transition just below the long-range ordering temperature in NCIO sample, The obtained characteristic flipping time of a single spin from both the law (Power law and Vogel-Fulcher law) and nonzero Vogel-Fulcher temperature (T0≃ 89.1 K) further verified the existence of cluster spin-glass behavior below the ordering temperature. The temperature evolution of phonon modes (up to 4 K) suggests that the phonon mode above the magnetic ordering temperature is mainly governed by the lattice degrees of freedom; notable renormalization of the mode frequency below the ordering temperature is due to the coupling of lattice with the underlying magnetic degrees of freedom.

(Invited) Towards an Expanded Palette of Materials and Mechanisms for Neuromorphic Computing

The metal-insulator transitions of electron correlated transition metal oxides provide an attractive vector for achieving large conductance switching with minimal energy dissipation. However, given the sparse and disconnected current knowledge of neuromorphic materials, a fundamental understanding of descriptors of neuromorphic function formulated in terms of intrinsic material properties, and the influence of atomistic defects on mesoscale domain evolution in the presence of external applied fields is currently lacking. Using VO2 and M x V2O5 compounds as model systems, I will detail our efforts to develop a systematic understanding of how compositional modifications through substitutional or interstitial doping alter transformation characteristics such as the transition temperature, magnitude of switching, energy dissipation, and hysteresis.The inclusion of dopant atoms strongly modifies the free energy landscapes in terms of relative phase stabilities, transformation barriers, and pathways; thereby profoundly altering the coupling of lattice, electronic, and spin degrees of freedom in a non-trivial manner. I will particularly focus on the three distinct mechanisms: (a) discovery of diffusive dopants that provide a distinctive new way to alter the dynamics of electronic transitions; (b) cation shuttling and polaron oscillation as a means of engendering metal—insulator transitions; and (c) lattice-anharmonicity-driven mechanisms in compounds with stereochemically active lone pairs. Acknowledgements: Research supported as part of REMIND, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under DE-SC0023353

Inducing Intermolecular Oxygen Coupling by Introducing S and FeOOH on Co(OH)2 Nanoneedle Arrays for Industrial Water Oxidation.

The design of electrocatalysts for oxygen evolution reaction (OER) remains a limitation of industrial hydrogen production by electrolysis of water. Excellent and stable OER catalysts can be developed by activating lattice oxygen and changing the reaction path. Herein, S and FeOOH on the Co(OH)2 nanoneedle arrays are introduced to construct a heterostructure (S-FeOOH/Co(OH)2/NF) as a proof of concept. Theoretical calculations and experimental suggest that the Co-O-Fe motif formed at the heterogeneous interface with the introduction of FeOOH, inducing electron transfer from Co to Fe, enhancing Co─O covalency and reducing intramolecular charge transfer energy, thereby stimulating direct intramolecular lattice oxygen coupling. Doping of S in FeOOH further accelerates electron transfer, improves lattice oxygen activity, and prevents dissolution of FeOOH. Consequently, the overpotential of S-FeOOH/Co(OH)2/NF is only 199mV at 10mA cm-2, and coupled with the Pt/C electrode can be up to 1 A cm-2 under 1.79V and remain stable for over 120h in an anion exchange membrane water electrolyzer (AEMWE). This work proposes a strategy for the design of efficient and stable electrocatalysts for industrial water electrolysis and promotes the commercialization of AEMWE.

Spin-Charge-Lattice Coupling across the Charge Density Wave Transition in a Kagome Lattice Antiferromagnet.

Understanding spin and lattice excitations in a metallic magnetic ordered system forms the basis to unveil the magnetic and lattice exchange couplings and their interactions with itinerant electrons. Kagome lattice antiferromagnet FeGe is interesting because it displays a rare charge density wave (CDW) deep inside the antiferromagnetic ordered phase that interacts with the magnetic order. We use neutron scattering to study the evolution of spin and lattice excitations across the CDW transition T_{CDW} in FeGe. While spin excitations below ∼100 meV can be well described by spin waves of a spin-1 Heisenberg Hamiltonian, spin excitations at higher energies are centered around the Brillouin zone boundary and extend up to ∼180 meV consistent with quasiparticle excitations across spin-polarized electron-hole Fermi surfaces. Furthermore, c-axis spin wave dispersion and Fe-Ge optical phonon modes show a clear hardening below T_{CDW} due to spin-charge-lattice coupling but with no evidence of a phonon Kohn anomaly. By comparing our experimental results with density functional theory calculations in absolute units, we conclude that FeGe is a Hund's metal in the intermediate correlated regime where magnetism has contributions from both itinerant and localized electrons arising from spin polarized electronic bands near the Fermi level.

Lattice battery solar cells: Exceeding Shockley–Queisser limit

AbstractA revolutionary concept of lattice battery solar cell (LBSC) is proposed to leap the conversion efficiency by inherently eliminating two major energy losses of conventional solar cells, namely hot carriers and non‐absorption of the substantial near infrared (NIR) emission. In an LBSC, hot phonon emission will be saved into lattice energy reservoir (LER) through electron–lattice coupling; NIR solar emission is harvested by an NIR‐perovskite composition. The NIR‐generated carriers are upconverted to the conduction band of perovskites driven by LER. The theoretical efficiency of LBSCs is estimated to be over 70%, significantly exceeding the Shockley–Queisser limit. In addition, LBSCs have lower operational temperature, resulting in much improved stability due to the elimination of heating sources from hot carriers. Different from the existing multijunction solar cells, LBSCs will keep the single layer structure with low‐cost fabrication. Therefore, LBSCs could perfectly satisfy the golden triangle of solar cell performance, which prospects great competitive advantage for further commercialization.

NC Loaded PtM Alloy from M-NC with Ultralow Pt Loading for Oxygen Reduction Reaction

Developing low Pt or non-precious metal catalysts for oxygen reduction reaction (ORR) has becoming necessary in recent years. Herein, PtM alloy anchored on nitrogen-doped carbon (PtM/NC, M=Fe, Co) catalyst with ultralow Pt loading (∼1 wt%) is prepared from the simple two-process pyrolysis, namely from C to M-NC then to PtM/NC. The as-prepared PtM/NC (M=Fe, Co) shows an excellent ORR catalytic performance with the peak potential and half-wave potential of 0.901 and 0.870 V for PtFe/NC, 0.868 and 0.845 V for Pt3Co/NC. The ORR on PtM/NC (M=Fe, Co) is a mainly direct 4-electron reaction pathway (3.75–3.90) in alkaline solution. Moreover, they possess good methanol tolerance and stability. Synergistic effect of Pt and M together with N species result in the excellent ORR catalytic activity of PtM/NC (M=Fe, Co). The negative shift of Pt binding energy caused by both lattice contraction and electron orbital coupling from M is beneficial for reducing the d-band center of Pt, weakening the oxygen binding energy and enhancing the ORR intrinsic activity of Pt. The strong interactions between NC and PtM alloy are beneficial for anchoring PtM nanoparticles, promoting the stability of catalyst. This work provides a new strategy for preparing ultralow Pt loading catalysts.

Improved electrical transport properties of La0.7Ca0.3−xKxMnO3 (0.0 ≤ x ≤ 0.3) films grown on La0.3Sr0.7Al0.65Ta0.35O3 (00l) substrates by sol–gel spin coating method

Herein, La0.7Ca0.3−xKxMnO3 (LCKMO) films with highly oriented growth were prepared on La0.3Sr0.7Al0.65Ta0.35O3 (00l) substrates by sol–gel spin coating method. Comprehensive analysis of microstructure, surface morphology, ion valence, and electrical transport properties of LCKMO films indicates that the substitution of K+ ions for Ca2+ ions increased the ratio of Mn4+/(Mn3+ + Mn4+), narrowed the one electron bandwidth, and enhanced double exchange mechanism and electron–lattice coupling. Moreover, the doping of K+ ions induced the dense and uniform conical-structured growth of grains on the surface of the films. Results demonstrated that at x = 0.1, LCKMO film exhibited the maximum TCR of 17.84% K−1 at 253.07 K, which was 31.76% higher than that of previously reported La1−x−yCaxKyMnO3 ceramic with the highest TCR. Further theoretical insights into the effects of Ca/K co-doping on electrical transport properties were supplemented.

Topological and compositional disorder induced exciton Anderson localization highly enhances luminescence quantum yields of alloyed perovskite nanocrystals

Anderson localization has inspired tremendous effort in exploring underlying physics regarding electron, atom, and photon transport in disordered lattices. However, due to the difficulty in implementing periodic trapping potential for neutral excitons, observing Anderson localization of excitons in disordered semiconductors remains challenging. We report evidence of Anderson localization of Frenkel excitons in the alloyed perovskite nanocrystals that possess high topological and compositional disorder. The broken symmetry-driven constructive interference of scattered exciton wavefunctions around the octahedrons induces strong exciton localization and, consequently, exciton–phonon coupling. This causes significant promotion of the luminescence quantum efficiency from 30% to an impressive 75% owing to enhanced radiative and suppressed nonradiative quantum transition rates. These findings clarify that both Anderson localization and exciton–lattice coupling play key roles in triggering immobility of Frenkel excitons in disordered wide-bandgap semiconductors and guide design of monocomponent warm white light emitters based on highly efficient alloyed perovskite nanocrystals.

Magnet-in-ferroelectric crystals exhibiting photomultiferroicity

Growing crystallographically incommensurate and dissimilar organic materials is fundamentally intriguing but challenging for the prominent cross-correlation phenomenon enabling unique magnetic, electronic, and optical functionalities. Here, we report the growth of molecular layered magnet-in-ferroelectric crystals, demonstrating photomanipulation of interfacial ferroic coupling. The heterocrystals exhibit striking photomagnetization and magnetoelectricity, resulting in photomultiferroic coupling and complete change of their color while inheriting ferroelectricity and magnetism from the parent phases. Under a light illumination, ferromagnetic resonance shifts of 910 Oe are observed in heterocrystals while showing a magnetization change of 0.015 emu/g. In addition, a noticeable magnetization change (8% of magnetization at a 1,000 Oe external field) in the vicinity of ferro-to-paraelectric transition is observed. The mechanistic electric-field-dependent studies suggest the photoinduced ferroelectric field effect responsible for the tailoring of photo-piezo-magnetism. The crystallographic analyses further evidence the lattice coupling of a magnet-in-ferroelectric heterocrystal system.

Inelastic neutron scattering study of magnon excitation by ultrasound injection in yttrium iron garnet

The magnon excitation by ultrasound injection in Y3Fe5O12 is studied by inelastic neutron scattering. Both longitudinal and transverse ultrasound injections enhanced the inelastic neutron scattering intensity. We analyzed the nonequilibrium magnon steady state using the effective magnon temperature model. The large deviation of the effective magnon temperature from the sample temperature is observed at the ultrasound longitudinal mode along [0, 0, 1] at ∼10 K and [1, 1, 1] at ∼140 K. This dependence suggests that the nonequilibrium steady state can be achieved only by strong spin–lattice coupling in Y3Fe5O12. The spin–lattice coupling exhibits a decrease largely above 100 K, indicating that it could be the main origin of the degradation of longitudinal spin Seebeck effect at the temperature range.

La(Fe,Si/Al)13-based materials with exceptional magnetic functionalities: a review

The field of magnetic functional materials continues to garner significant attention due to its research and diverse applications, such as magnetic storage and spintronics. Among these, La(Fe,Si/Al)13-based materials exhibit abundant magnetic properties and emerge as highly captivating subjects with immense potential. This review provides an overview of the diverse magnetic structures and itinerant electron metamagnetic transition observed in La(Fe,Si/Al)13-based materials. The transformation of different magnetic configurations elicits the phenomena such as negative thermal expansion, magnetostriction, magnetocaloric effect, and barocaloric effect. In addition, the pivotal role of spin and lattice coupling in these phenomena is revealed. The magnetic functionalities of La(Fe,Si/Al)13-based materials can be controlled through adjustments of magnetic exchange interactions. Key methods, including chemical substitution, external field application, and interstitial atom insertion, enable precise modulation of these functionalities. This review not only provides valuable insights into the design and development of magnetic functional materials but also offers significant contributions to our understanding of the underlying mechanisms governing their magnetic behaviors.

Polymorphic Kondo Effects Driven by Spin Lattice Coupling in VTe2

AbstractPolymorphism in transition metal dichalcogenides (TMDs) allows unique physical properties to be controlled, such as artificial heavy fermion phenomena, the quantum spin Hall effect, and optimized device operations with 2D materials. Besides lattice structural and metal‐semiconductor polymorphs, intriguing charge density wave (CDW) states with different electronic and magnetic phases are demonstrated in TMDs. Typically, the “normal” state is stabilized at high temperature above the CDW energy scale, and therefore, is not relevant to many low‐temperature quantum phenomena, such as magnetic ordering and the heavy fermion Kondo state. Here, a local and robust phase manipulation of the normal (1T) and CDW (1T’) states of VTe2 is reported by laser irradiation, and polymorphic Kondo effects are demonstrated with the two phases at low temperatures. The theoretical calculations show that Kondo screening of vanadium 3d electron moments is markedly enhanced in 1T’‐VTe2, which is responsible for the observed transport properties distinct from its 1T counterpart. Controlling the spin‐lattice coupling and Kondo physics via laser‐driven CDW phase patterning allows the design of correlated electronic and magnetic properties in TMDs.

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films.

Incorporating hydrogen into transition-metal oxides (TMOs) provides a facile and powerful way to manipulate the performances of TMOs, and thus numerous efforts have been invested in developing hydrogenation methods and exploring the property modulation via hydrogen doping. However, the distribution of hydrogen ions, which is a key factor in determining the physicochemical properties on a microscopic scale, has not been clearly illustrated. Here, focusing on prototypical perovskite oxide (NdNiO3 and La0.67Sr0.33MnO3) epitaxial films, we find that hydrogen distribution exhibits an anomalous "uphill" feature (against the concentration gradient) under tensile strain, namely, the proton concentration enhances upon getting farther from the hydrogen source. Distinctly, under a compressive strain state, hydrogen shows a normal distribution without uphill features. The epitaxial strain significantly influences the chemical lattice coupling and the energy profile as a function of the hydrogen doping position, thus dominating the hydrogen distribution. Furthermore, the strain-(H+) distribution relationship is maintained in different hydrogenation methods (metal-alkali treatment) which is first applied to perovskite oxides. The discovery of strain-dependent hydrogen distribution in oxides provides insights into tailoring the magnetoelectric and energy-conversion functionalities of TMOs via strain engineering.

Charge-lattice coupling effects in organic isomeric charge transfer crystals

One of the most important features of organic cocrystals is the interaction between electrons and lattices, which brings interesting physical phenomena. In this work, we prepared two isomeric crystals in which the isomeric donors are used to fabricate charge transfer crystals. Isomeric crystals present different electron–lattice coupling strengths to further affect the charge localization, which leads to different dielectric constants and fluorescence lifetimes. Furthermore, external magnetic field and electric field exhibit different tunability on the photoluminescence and dielectric constants of the isomeric cocrystals due to the significant differences in the coupling between the charge and lattice vibration. Overall, through fabricating isomeric organic crystals, neighbor molecular vibration dependence of electron–lattice coupling is studied, which provides a platform to further understand the lattice vibration dependent spin and optics.

Polaron Vibronic Progression Shapes the Optical Response of 2D Perovskites.

The optical response of 2D layered perovskites is composed of multiple equally-spaced spectral features, often interpreted as phonon replicas, separated by an energy Δ ≃ 12 - 40meV, depending upon the compound. Here the authors show that the characteristic energy spacing, seen in both absorption and emission, is correlated with a substantial scattering response above ≃200cm-1 (≃25meV) observed in resonant Raman. This peculiar high-frequency signal, which dominates both Stokes and anti-Stokes regions of the scattering spectra, possesses the characteristic spectral fingerprints of polarons. Notably, its spectral position is shifted away from the Rayleigh line, with a tail on the high energy side. The internal structure of the polaron consists of a series of equidistant signals separated by 25-32cm-1 (3-4meV), depending upon the compound, forming a polaron vibronic progression. The observed progression is characterized by a large Huang-Rhys factor (S >6) for all of the 2D layered perovskites investigated here, indicative of a strong charge carrier - lattice coupling. The polaron binding energy spans a range ≃20-35meV, which is corroborated by the temperature-dependent Raman scattering data. The investigation provides a complete understanding of the optical response of 2D layered perovskites via the direct observation of polaron vibronic progression. The understanding of polaronic effects in perovskites is essential, as it directly influences the suitability of these materials for future opto-electronicapplications.

The Study of Temperature-Dependent Magnetic Properties Variation in CoCr2O4 Nanoparticles with (y = 0.8) and Without Coating Concentration of Non-Magnetic (SiO2)y

Abstract The present study investigates the temperature-dependent magnetic (MT) properties of CoCr2O4/(SiO2)y (y = 0 and 0.8) nanoparticles. Nanoparticles were synthesised by using the conventional sol–gel technique. The X-ray diffraction (XRD) method confirmed the normal spinel structure of CoCr2O4 nanoparticles. The main peak analysis of the XRD pattern using Debye–Scherrer’s formula probes the mean crystallite sizes for coated and uncoated nanoparticles, and the sizes based on which the probes have been carried out amount to 19 nm and 28 nm, respectively. The transmission electron microscopy (TEM) image showed the non-spherical shape of these nanoparticles. Field-cooled (FC) and zero field-cooled (ZFC) MT plots were taken by using a superconducting quantum interference device (SQUID) magnetometer. Pure CoCr2O4 nanoparticles showed the ferrimagnetic transition at Curie temperature (Tc = 99 K) on an applied field (H) of 50 Oe. Tc decreased up to 95 K with the increase in 80% SiO2 concentration in CoCr2O4 nanoparticles. For pure samples, conical spiral temperature (TS) and lock-in transition temperature (TL) remain unchanged with increasing magnetic field because of strong spin–lattice coupling. However, for 80% SiO2 impurity, the decrease in Tc was attributed to the reduction in surface disorder with a minor decline in TS and TL. The Ms declined with a decrease in temperature because of the existence of stiffed/strong conical spin-spiral and lock-in states in pure CoCr2O4 nanoparticles, while nanoparticles with 80% coating SiO2 concentration showed abnormal behavior. The coercivity increases with a decrease in temperature due to a decrease in thermal fluctuations at low temperatures for both samples. The fitting of coercivity (Hc) versus temperature plot by using Kneller’s law has given the values of coercivity constant (α) and coercivity at average blocking temperature (TB) for both samples, which are α = 0.54, TB = 75 K and α = 1.59, TB = 81 K, respectively. Hence, the increase in the concentration of SiO2 decreased nanoparticles size and surface disorder in CoCr2O4 nanoparticles while enhancing Ms below spin-spiral state ordering.

Interfacial lattice coupling engineering in all-inorganic coupled flexible films for dielectric energy storage

Hexagonal boron nitride (BN) was dispersed into the lattice of Sr2Bi4Ti5O18 (SBT) ferroelectrics to form all-inorganic flexible film capacitors. The interfacial lattice coupling in microscopic induces reconstruction of lattice and electron configuration. The electrons transfer interaction at the interfacial lattices results in the lattice stretching, thereby enhancing polyhedral dipole-dipole interactions. Meanwhile, the potential difference derived from the electron transfer provides driving force for the interfacial polarization. Above both effectively enhance the polarization without expense of breakdown strength. The interfacial lattice coupling greatly reduces the carrier generation rates under high electric field due to the ultra-high bandgap of BN, which further improves breakdown strength, thus, suppressing the inversed relationship. The recovery energy density of 119.7 J/cm3 and the efficiency of 71.2 % are obtained with a consecutive mechanical bending stability. This strategy provides an alternative to break through the inversed relationship between polarization and breakdown strength for all-inorganic flexible film capacitors.

Light Emission from CsPbBr3 Metal Halide Perovskite Nanocrystals Arises from Dual Emitting States with Distinct Lattice Couplings

Light Emission from CsPbBr₃ Metal Halide Perovskite Nanocrystals Arises from Dual Emitting States with Distinct Lattice Couplings