Defect Pairs Research Articles

A trade-off between migration and association energies for hydride-ion conductivity in the SrLiH3-CaLiH3-NaLiH2 system.

Hydride-ion (H-) conductors have garnered much attention owing to their high ionic conductivity and potential applications such as batteries and fuel/electrolysis cells. Perovskite-type H- conductors are known to exhibit relatively high ionic conductivity at room temperature. The present work demonstrated systematic material exploration within the SrLiH3-CaLiH3-NaLiH2 pseudo-ternary system. The Na-substituted system, Sr1-xNaxLiH3-x, exhibited a remarkable H- conductivity of 5.1 × 10-6 S cm-1 at 25 °C for Sr0.8Na0.2LiH2.8, marking the highest value reported among perovskite-type hydrides to date. Furthermore, we found a clear trend of enhanced H- conductivity with Ca substitution in the Sr1-xCaxLiH3 pseudo-binary system. However, in the Sr1-xCaxNayLiH3-y pseudo-ternary system, a negative synergistic effect of Ca and Na co-doping was observed. First-principles calculations revealed that this negative effect arises from a trade-off between migration and association energies in defect pairs of Na+ dopants and H- vacancies. These findings provide valuable insights into designing superior anion conductors.

High-Throughput Information Storage in an Intelligent Response Phosphor.

Persistent phosphor has emerged as a promising candidate for information storage due to rapid accessibility and low-energy requirements. However, the low storage capacity has limited its practical application. Herein, we skillfully designed and developed NaGdGeO4:Pb2+,Tb3+ stimulated phosphor by trace doped Sm3+. As expected, this phosphor demonstrates a larger carrier capacity than traditional commercial SrAl2O4:Eu2+,Dy3+ phosphors and superstrong thermostimulated luminescence (TSL) that is three times greater than its photoluminescence (PL) intensity (PL efficiency, 17.3%). A mechanism of the enhanced and controllable TSL is proposed based on electron-hole defect pair structure. We further present a high-throughput optical data recording in five dimensions in a single fluorescent film recording layer. The findings described here provide not only a universal approach for constructing TSL materials but also a new paradigm for future generation optical storage technology.

Half-integer topological defects paired via string micelles in polar liquids.

Ferroelectric nematic (NF) liquid crystals present a compelling platform for exploring topological defects in polar fields, while their structural properties can be significantly altered by ionic doping. In this study, we demonstrate that doping the ferroelectric nematic material RM734 with cationic polymers enables the formation of polymeric micelles that connect pairs of half-integer topological defects. Polarizing optical microscopy reveals that these string defects exhibit butterfly textures, featured with a 2D polarization field divided by Néel-type kink walls into domains exhibiting either uniform polarization or negative splay and bend deformations. Through analysis of electrophoretic motion and direct measurements of polarization divergences, we show that the string micelles are positively charged, and their side regions exhibit positive bound charges. To elucidate these observations, we propose a charge double-layer model for the string defects: the positively charged cationic polymer chains and densely packed RM734 molecules form a Stern charge layer, while small anionic ions and positive bound charges constitute the charge diffusion layer. Notably, our experiments indicate that only cationic polymer doping effectively induces the formation of these unique string defects. These findings enhance our understanding of ionic doping effects and provide valuable insights for engineering polar topologies in liquid crystal systems.

Irradiation Damage Evolution Dependence on Misorientation Angle for Σ 5 Grain Boundary of Nb: An Atomistic Simulation-Based Study

Abstract Niobium as refractory element holds ability to arrest the primary radiation damage in reactor's fissionable conditions and can withstand high-temperature applications. We have inclined the investigation of irradiated Nb Σ 5 symmetric-tilt angled grain boundary (STGB) models at two high-angled grain boundary misorientation: 53.13 deg (Σ 5(2–10)/(120)) and 36.87 deg (Σ 5(3–10)/(130)), respectively. A hybrid of Ziegler–Biersack–Littmark (ZBL) and embedded atom method (EAM) potentials were superimposed to simulate radiation damage. Statistical averaging of the displacement cascades was conducted to study the dynamic evolution of the point defects and interstitial clusters at varying magnitudes of primary knock-on atom (PKA) energies, irradiation temperatures, and PKA directions. The irradiated grain bounary (GB) models were compared with an irradiated bulk Nb specimen, and the results of the study indicate that the irradiated Nb system with greater misorientation angle, i.e., Nb Σ 5 (ɵ = 53.13 deg) survived with lower number Frenkel pair defects as well as the population small-sized interstitial clusters. The point defect cluster analysis indicated the highest population of interstitial clusters survived in Nb STGB models were irradiated along <1 3 5> PKA direction and 100 keV recoil energies respectively.

Understanding the in-gap defect states in the photo-generated electrons’ dynamics over two dimensional defective bismuth oxybromide

Defect engineering accelerates the solar CO2 reduction by regulating photogenerated electrons’ dynamics. Based on first-principles calculation, intrinsic characteristics of defects are investigated to understand the effects of point defects on electrons’ dynamics in defective BiOBr. We find that defect pair (Px), pairing point defect with neighboring Br vacancy (VBr), improves the stability. In-gap defect states are characterized by its occupation. Due to localized partially-occupied in-gap states, PO, PBi and PCu facilitate photogenerated electrons’ trapping and inhibit photogenerated carriers’ recombination. Aggregated electrons around the defects promote the charge transfer to absorbed CO2. PO (PBi) is an effective n-type (p-type) doping with shallow donor (acceptor) state deriving from localized partially-occupied in-gap tv (av) states. PCu possesses localized in-gap defect state which derives from spin-polarized anti-bonding dx2-y2 state. Both PPb and VBr have little impact on the photogenerated electrons’ trapping due to the absence of localized partially-occupied in-gap states. Our findings provide comprehensive knowledge of defect physics for rational design of photocatalysts.

Aliovalent doping engineering to synergistically optimize the energy storage properties of Sr0.7Bi0.2TiO3-based linear-like relaxor ferroelectric ceramics

Dielectric capacitors with high energy storage density and power density are essential for the miniaturization and lightweight design of electronic devices. However, current applications are hampered by the challenge of simultaneously achieving high recoverable energy storage density and efficiency, as well as the fact that many dielectric energy storage ceramics contain lead elements. In this study, a multiple optimization strategy is proposed to significantly increase the breakdown strength while maintaining a high polarization strength by forming Bi3+-Li+ defect pairs to disrupt the paraelectric phase, and by introducing aliovalent double ions Li+ and La3+ to increase the cationic disorder. The change of domain structure and the relaxation enhancement mechanism is analyzed by dielectric properties and first-order reversal curve. Band gap, impedance and numerical simulations reveal the breakdown strength enhancement mechanism. As a result, the ceramics achieve a remarkable combination of high Wrec of 4.4 J/cm3 and high ƞ of 90 % at 420 kV/cm. Furthermore, the ceramic exhibits exceptional stability and fatigue resistance. Notably, the ceramic obtains a power density of 99.5 MW/cm3 and a rapid discharge rate of 0.22 µs. These findings demonstrate the excellent potential of Sr0.7Bi0.2TiO3-based ceramics as an alternative to Pb-based ceramics, and provide an effective strategy for developing advanced energy storage materials.

Radiation protection of W–Al composite films/coatings for aviation using genetic algorithms

This study evaluated electron shielding capabilities of various materials using Geant4 Monte Carlo software. By analyzing materials with different atomic numbers, we designed and tested composite films and coatings for radiation protection. Under 1.2 MeV electron irradiation, these materials reduced the dose deposited in electronic components by over 70 %. The fabricated composite films (W–Al) reduced the actual total dose by 100 % with a 30.67 % mass increase, closely matching the simulation result of 75.36 %. The composite coatings (W–Al) reduced the dose by 89.2 % with a 33 % mass increase, matching the simulation result of 70 %. Cascade collision simulations revealed that higher PKA energies lead to longer times to reach the thermal peak, more peak defects, and more stable defect pairs. This is due to the displacement threshold energy of the atoms in aluminum and tungsten. These results demonstrate the effectiveness of our composite films and coatings in enhancing electron shielding performance and validate our design methods.

Bjerrum defects in s-II gas hydrate

The energy and structure of Bjerrum defects in structure II gas hydrates were investigated by using first-principle calculations for finite-size clusters and periodic 3D lattice systems. The formation energies of these defects were calculated for the first time when the cages of the structure II structure were completely empty and the large cage was filled with a THF molecule. Analogous to findings in ice structures, one of the hydrogen atoms forming the D defect was noted to orient toward the cage. If the excess proton resides in the large cage, it acts as an attraction center for the polar guest molecule, i.e., THF. Therefore, the large cage guest THF molecule stabilizes the D/L defect pair and isolated D/L defect formation energies by forming hydrogen bonds with the D defect. In such cases, the defect structure representing a D/L defect pair containing a THF molecule interacting with one of the hydrogen atoms of the D defect mirrors the guest-induced ones. Notably, the classical Bjerrum defect and the guest-induced Bjerrum defect exhibit a similar phenomenon in defective structures. Contrary to existing literature, it is evident that guest-induced Bjerrum defects involve both the L and D components. The insights gained from this study could potentially offer an alternative perspective to understand various experimental observations, such as those related to dielectric and NMR properties.

Free energy formulae for confined nematic liquid crystals based on analogies with Kirchhoff–Routh theory in vortex dynamics

Active nematics are influenced by alignment angle singularities called topological defects. The localization of these defects is of major interest for biological applications. The total distortion of alignment angles due to defects is evaluated using Frank free energy, which is one of the criteria used to determine the location and stability of these defects. Previous work used the line integrals of a complex potential associated with the alignments for the energy calculation (Miyazako and Nara 2022 R. Soc. Open Sci . 9 , 211663 (doi: 10.1098/rsos.211663 )), which has a high computational cost. We propose analytical formulae for the free energy in the presence of multiple topological defects in confined geometries. The formulae derived here are an analogue of Kirchhoff–Routh functions in vortex dynamics. The proposed formulae are explicit with respect to the defect locations and conformal maps, which enable the explicit calculation of the energy extrema. The formulae are applied to calculate the locations of defects in so-called doublets and triplets by solving simple polynomial formulae. A stability analysis is also conducted to detect whether defect pairs with charges ± 1 / 2 are stable or unstable in triplet regions. Our numerical results are shown to match the experimental results (Ienaga et al. 2023 Soft Matter 19 , 5016–5028. (doi: 10.1039/d3sm00071k )).

Chemistry of Formate and Water Ligands on Metal Oxide Cluster Nodes of Metal-Organic Framework hcp Hf-UiO-66: Keys to Understanding Reactivity of Paired μ2-OH and Defect Sites.

Many metal-organic frameworks (MOFs) incorporate nodes that are metal oxide clusters, and ligands that have been observed on these nodes include formates, acetates, water, hydroxyl groups, and others, all of which are potentially important in affecting reactivities for applications in separations, catalysis, and sensing. Formate is a common node ligand, arising from formic acid used as a modulator and from N,N-dimethylformamide used as a solvent in MOF syntheses. Yet only little work has been reported characterizing the reactivities of node formate ligands. Infrared spectra reported here show that formate bonds to two types of sites on the paired Hf6O8 nodes of hcp UiO-66, namely, defect and μ2-OH sites. Quantifying the number of formate ligands by 1H NMR spectroscopy of digested samples showed an almost equal number of formate ligands on the two sites, indicating the likelihood that they neighbor each other. These formate ligands interact with water molecules, reversibly switching their bonding from bidentate to monodentate. The formates on μ2-OH sites of hcp Hf-UiO-66 interact much more strongly with water than those on defect sites of the same node, and both interact more strongly than isolated defect sites of Hf-UiO-66. Correspondingly, the catalytic activities of hcp UiO-66 determined as turnover frequencies on each site are approximately twofold higher than those on UiO-66, bolstering the inference that methanol dehydration is catalyzed by a node defect site and a neighboring node μ2-OH site. The results show how MOFs, with their well-defined node structures, provide unprecedented opportunities to understand details of reactivities and catalysis on metal oxide clusters, in contrast to bulk metal oxide surfaces.

Nature of Scapolite Color: Ab Initio Calculations, Spectroscopy, and Structural Study

The article describes the results of a comprehensive study of the extra-framework components of scapolites using quantum–chemical calculations, electronic and vibrational spectroscopy, and single-crystal X-ray diffraction and crystal structure refinement. The ab initio calculations were performed using an embedded-cluster approach of extra-framework components in various cation surroundings. As a result, through comparing the experimental and ab initio calculation results, the energies of the electronic and vibrational transitions of various extra-framework components (CO3)2−, (CO3)·−, S3·−, S2·−—as well as the role of these components in the process of the lowering of the symmetry—were determined for scapolites belonging to the marialite–meionite solid–solution series. The nature of the various colors of the scapolites has also been established. Colors from purple to blue are a result of the presence of radiation-induced pairs of defects: carbonate radical anions (CO3)·− and F-centers. However, polysulfide S3·− radical anions are found in some violet scapolites.

Defect fusion and Casimir energy in higher dimensions

We study the operator algebra of extended conformal defects in more than two spacetime dimensions. Such algebra structure encodes the combined effect of multiple impurities on physical observables at long distances as well as the interactions among the impurities. These features are formalized by a fusion product which we define for a pair of defects, after isolating divergences that capture the effective potential between the defects, which generalizes the usual Casimir energy. We discuss general properties of the corresponding fusion algebra and contrast with the more familiar cases that involve topological defects. We also describe the relation to a different defect setup in the shape of a wedge. We provide explicit examples to illustrate these properties using line defects and interfaces in the Wilson-Fisher CFT and the Gross-Neveu(-Yukawa) CFT and determine the defect fusion data thereof.

General algorithm for characterization of donor-acceptor pair recombination processes in solid-state materials

Radiative recombination processes can occur in solid-state systems through the pairing of donor and acceptor defects of the lattice. Recently, donor-acceptor pairs (DAP) have been proposed as promising candidates for quantum applications, and their signature has been observed in emerging low-dimensional materials. Therefore, the identification of such processes is gaining interest and requires methods to efficiently and reliably characterize them. Here, we introduce a general algorithm to identify DAP processes starting from the experimental photoluminescence (PL) emission spectrum and basic material parameters, including the lattice structure and dielectric constant. The algorithm recognizes possible DAP transitions from the emission pattern in the spectrum and returns the characteristic energy of the DAP transition and the separation between the donor and acceptor sites. By testing the algorithm on the photoluminescence spectrum of hexagonal boron nitride (hBN), we show that our method is robust against experimental errors and adds new capabilities to the investigation toolbox of semiconductors and their optical properties.

High-resolution three-dimensional imaging of topological textures in nanoscale single-diamond networks.

Topological defects-extended lattice deformations that are robust against local defects and annealing-have been exploited to engineer novel properties in both hard and soft materials. Yet, their formation kinetics and nanoscale three-dimensional structure are poorly understood, impeding their benefits for nanofabrication. We describe the fabrication of a pair of topological defects in the volume of a single-diamond network (space group Fd m) templated into gold from a triblock terpolymer crystal. Using X-ray nanotomography, we resolve the three-dimensional structure of nearly 70,000 individual single-diamond unit cells with a spatial resolution of 11.2 nm, allowing analysis of the long-range order of the network. The defects observed morphologically resemble the comet and trefoil patterns of equal and opposite half-integer topological charges observed in liquid crystals. Yet our analysis of strain in the network suggests typical hard matter behaviour. Our analysis approach does not require a priori knowledge of the expected positions of the nodes in three-dimensional nanostructured systems, allowing the identification of distorted morphologies and defects in large samples.

Definitive engineering strength and fracture toughness of graphene through on-chip nanomechanics

Fail-safe design of devices requires robust integrity assessment procedures which are still absent for 2D materials, hence affecting transfer to applications. Here, a combined on-chip tension and cracking method, and associated data reduction scheme have been developed to determine the fracture toughness and strength of monolayer-monodomain-freestanding graphene. Myriads of specimens are generated providing statistical data. The crack arrest tests provide a definitive fracture toughness of 4.4 MPam\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{{{{{{\\rm{m}}}}}}}$$\\end{document}. Tension on-chip provides Young’s modulus of 950 GPa, fracture strain of 11%, and tensile strength up to 110 GPa, reaching a record of stored elastic energy ~6 GJ m−3 as confirmed by thermodynamics and quantized fracture mechanics. A ~ 1.4 nm crack size is often found responsible for graphene failure, connected to 5-7 pair defects. Micron-sized graphene membranes and smaller can be produced defect-free, and design rules can be based on 110 GPa strength. For larger areas, a fail-safe design should be based on a maximum 57 GPa strength.

Insights into Antisite Defect Complex Induced High Ferro-Piezoelectric Properties in KNbO3 Perovskite: First-Principles Study.

Improving ferro-piezoelectric properties of niobate-based perovskites is highly desirable for developing eco-friendly high-performance sensors and actuators. Although electro-strain coupling is usually obtained by constructing multiphase boundaries via complex chemical compositions, defect engineering can also create opportunities for novel property and functionality advancements. In this work, a representative tetragonal niobate-based perovskite, i.e., KNbO3, is studied by using first-principles calculations. Two intrinsic types of Nb antisite defect complexes are selected to mimic alkali-deficiency induced excess Nb antisites in experiments. The formation energy, electronic profiles, polarization, and piezoelectric constants are systematically analyzed. It is shown that the structural distortion and chemical heterogeneity around the energetically favorable antisite pair defects, i.e., (NbK4·+KNb4'), lower the crystal symmetry of KNbO3 from tetragonal to triclinic phase, and facilitate polarization emergence and reorientation to substantially enhance intrinsic ferro-piezoelectricity (i.e., spontaneous polarization Ps of 68.2 μC/cm2 and piezoelectric strain constant d33 of 228.3 pC/N) without complicated doping and alloying.

Defect Pairs in Boron Nitrides That Exhibit Strong Electronic Transitions in the Infrared

Defect Pairs in Boron Nitrides That Exhibit Strong Electronic Transitions in the Infrared

Detecting phase transitions in lattice gauge theories: Production and dissolution of topological defects in 4D compact electrodynamics

We present the application of microcanonical inflection point analysis (MIPA)—a novel and powerful method for the systematic identification and classification of phase transitions (PTs)—to the microcanonical formulation of lattice gauge theories. Specifically, we explore how this approach sheds light on collective phenomena such as the emergence of topological order in quantum field theories. As a case study, we show how to systematically characterize PTs in 4D U(1) lattice electrodynamics. Beyond identifying the well-established deconfinement PT (DPT) associated with pair dissolution, classified as a first-order PT, we uncover two higher-order PTs not observed before. Thanks to the application of the MIPA, we identify an independent third-order PT in the confined phase and indications of a dependent third-order PT in the deconfined (Coulomb) phase. To gain physical insights into these PTs, we numerically compute the average number density of monopolar and pair defects as a function of energy. Notably, our findings reveal that the pair dissolution mechanism extends beyond a singular transitional phenomenon coinciding with the DPT. Instead, it encompasses a spectrum of transitional phenomena, as indicated by the rates of acceleration and deceleration in the dissolution of pairs as a function of energy. Finally, we briefly discuss how such a method can be extended to more complex quantum field theories on a lattice. Published by the American Physical Society 2024

Ising fracton spin liquid on the honeycomb lattice

We study a classical Ising model on the honeycomb lattice with local two-body interactions and present strong evidence that at low temperature it realizes a higher-rank Coulomb liquid with fracton excitations. We show that the excitations are (type-I) fractons, appearing at the corners of membranes of spin flips. Because of the threefold rotational symmetry of the honeycomb lattice, these membranes can be locally combined such that no excitations are created, giving rise to a set of ground states described as a liquid of membranes. We devise a cluster Monte Carlo algorithm purposefully designed for this problem that moves pairs of defects, and use it to study the finite-temperature behavior of the model. We show evidence for a first order transition from a high-temperature paramagnet to a low-temperature phase whose correlations precisely match those predicted for a higher-rank Coulomb phase. Published by the American Physical Society 2024

SCC3 is an axial element essential for homologous chromosome pairing and synapsis

Cohesin is a multi-subunit protein that plays a pivotal role in holding sister chromatids together during cell division. Sister chromatid cohesion 3 (SCC3), constituents of cohesin complex, is highly conserved from yeast to mammals. Since the deletion of individual cohesin subunit always causes lethality, it is difficult to dissect its biological function in both mitosis and meiosis. Here, we obtained scc3 weak mutants using CRISPR-Cas9 system to explore its function during rice mitosis and meiosis. The scc3 weak mutants displayed obvious vegetative defects and complete sterility, underscoring the essential roles of SCC3 in both mitosis and meiosis. SCC3 is localized on chromatin from interphase to prometaphase in mitosis. However, in meiosis, SCC3 acts as an axial element during early prophase I and subsequently situates onto centromeric regions following the disassembly of the synaptonemal complex. The loading of SCC3 onto meiotic chromosomes depends on REC8. scc3 shows severe defects in homologous pairing and synapsis. Consequently, SCC3 functions as an axial element that is essential for maintaining homologous chromosome pairing and synapsis during meiosis.