Lattice Defects Research Articles

Crystal structure and magnetic properties of Fe doped BaTiO3 at morphotropic phase boundary

Ceramic compounds BaTi1-xFexO with x = 0 – 0.2 prepared by solid state reaction technique were studied using X-ray diffraction, Raman spectroscopy, and magnetometry methods focusing on the correlation between the structure and magnetic properties. Chemical doping with Fe ions leads to a concentration driven structural transformation from the single phase tetragonal (T-) structure to the hexagonal (H-) structure with a mixed structural state stable in the concentration range 0.06 <x ≤ 0.2. Increase in the Fe ions content causes a stabilization of weak ferromagnetic state driven by the exchange interactions Fe3+ – O – Fe3+ ions strongly dependent on the structural positions of the Fe ions. Increase of the dopant content above x = 0.08 leads to a decrease of the remnant magnetization which is mainly caused by a stabilization of Fe4+ ions as well as by the lattice defects associated with oxygen vacancies formed to keep electroneutrality of the compounds. The results of the structural and magnetization measurements allowed to itemize the type of exchange interactions between Fe ions residing different structural positions of the hexagonal lattice as well as to reveal structural instability of the T- and H- phases under ambient conditions and applied electric field which shows a possibility to control the structure and magnetic properties of the mixed compounds via external stimuli.

Engineering the structure defects of ceria-zirconia-praseodymia solid solutions for diesel soot catalytic elimination

Creating structure defects in ceria-based solid solution catalysts is a crucial yet challenging task. Herein, urea-assisted synthesis strategy was designed for ceria-zirconia-praseodymia catalyst (CeZrPrOx) to create lattice defects; its effects on catalyst structure, physical-chemical properties and catalytic diesel soot purification activity were systematically investigated. Raman and X-ray photoelectron spectroscopy (XPS) findings indicate that the urea-assisted synthesized catalyst (CeZrPrOx-U) has remarkably more Ce3+ proportion (structure defects), oxygen vacancies and surface reactive oxygen species (O22- and O2-). Temperature-programmed reduction by hydrogen (H2-TPR) and temperature-programmed desorption by oxygen (O2-TPD) results further prove that the oxygen migration of the CeZrPrOx-U is definitely enhanced. Compared to the conventional CeZrPrOx catalyst, the bulk lattice oxygen of the CeZrPrOx-U can be migrated to the surface to generate surface reactive oxygen species more easily. As a consequence, the prepared CeZrPrOx-U catalyst exhibits obviously better catalytic diesel soot purification activity. Therefore, this study suggests that engineering the structure defects in CeZrPrOx catalyst is an effective approach to improve physical-chemical properties and enhance the soot catalytic elimination activity of the catalyst.

Critical Role of Long-Range Strain-Induced Interactions in Stabilizing Zener Ordering

Abstract As a fundamental theory for structural transformations, the Zener ordering of interstitials in a body-centered cubic host lattice, which was established more than half a century ago, has been challenged by recent first-principles investigations. In this Letter, we rigorously prove the existence of the Zener ordering via Monte Carlo simulations with complete interstitial interactions and demonstrate the critical role of long-range indirect strain-induced interactions in stabilizing the Zener ordering. These insights improve our understanding of the self-induced collective ordering of point defects in a host lattice, and complete the fundamental physics of alloys and order-disorder phase transitions.

Direct Regeneration of Industrial LiFePO4 Black Mass Through A Glycerol‐Enabled Granule Reconstruction Strategy

AbstractWith the increasing sales of electric vehicles, lots of spent lithium‐ion batteries (LIBs) assembled with LiFePO4 (LFP) cathodes will retire in the next few years, posing a significant challenge for their effective and environmentally‐friendly recycling. The main reason why spent LFP cathodes fail to re‐utilize lies in the lattice defects caused by lithium loss and structural defects resulting from stress accumulation. In this work, we propose an in situ granule reconstruction strategy to directly regenerate spent LFP black mass (S−BM) using glycerol in industry settings. The hydroxyl groups abundant in glycerol serves as electron donor that help reduce Fe (III) and repair Fe−Li antisite defects (FeLi). Additionally, the chelating properties of glycerol intervene with structurally disintegrated particles, inhibiting Oswald ripening effect and promoting bonding of grain boundaries to generate lamellar microcrystals with homogeneous grain size, recover their morphology and crystal structure after a facile annealing procedure. Furthermore, the regenerated LFP restores Fe−O bonds which further inhibits structural distortion and improve Li+ migration kinetics. As a result, the regenerated industrial LFP black mass (R−BM) exhibits superior lithium storage performance with a discharge capacity of 123.2 mA h g−1 after 500 cycles at 5.0 C (a capacity retention rate of 93.1 %).

High-Performance Giant InP Quantum Dots with Stress-Released Morphological ZnSe-ZnSeS-ZnS Shell.

Indium phosphide (InP) quantum dots (QDs) are increasingly considered potent alternatives to traditional cadmium-based QDs. Notwithstanding, the material stability of InP, especially when juxtaposed with its cadmium-based counterparts, poses significant challenges in its application. Generally, a thick ZnS shell is applied to InP cores to thwart photo-oxidation and diminish nonradiative recombination. Yet, the pronounced lattice mismatch between the InP core and the ZnS shell can introduce lattice defects, consequently attenuating the luminescence efficiency. This makes the cultivation of a flawless thick shell a paramount challenge. In the present research, a synthetic methodology is elucidated to fabricate highly efficient InP QDs with dimensions exceeding 20nm, achieved by alleviating the lattice mismatch strain during the shell growth. By regulating the shell composition and morphology, InP/ZnSe/ZnSeS/ZnS QDs with shield-like morphology are prepared and demonstrate a photoluminescence quantum yield (PLQY) of ≈90%, exhibiting significantly enhanced photostability and thermal stability. This discovery is expected to greatly advance the preparation of highly efficient InP-based or other QDs, expanding their potential in various applications such as environmentally friendly displays and energy-saving lighting.

One-Pot Synthesis of (CrMnFeCoNi)Ox High-Entropy Oxides for Efficient Catalytic Oxidation of Propane: A Promising Substitute for Noble Metal Catalysts.

The efficient catalytic oxidation of propane, as a short-chain alkane, remains challenging in environmental catalysis. High-entropy oxides (HEOs) exhibit advantages in abundant and well-dispersed elemental composition, exceptional thermal stability, and enriched lattice defects. Herein, (CrMnFeCoNi)Ox HEO catalysts are successfully synthesized by using a continuous hydrothermal flow synthesis (CHFS) route, without any subsequent calcination processes. This route yields HEOs with fine particle sizes, high specific surface areas, and abundant near-surface lattice oxygen compared to the traditional coprecipitation method. Notably, the propane conversion over the CHFS-made (CrMnFeCoNi)Ox HEO reaches 90% at 255 °C, with an apparent activation energy of 53.2 kJ/mol, mainly attributed to its enriched lattice oxygen and enhanced oxygen mobility that prevent the accumulation of acetates and the consequent occupation of active sites. In comparison to commercial Pt/Al2O3 and Pd/Al2O3, (CrMnFeCoNi)Ox HEO demonstrates exceptional activity and can maintain long-term stability under high-temperature (upon 650 °C) and moisture-rich conditions (at 2-10 vol %). These attributes highlight its potential as a promising substitute for noble metal catalysts in industrial applications.

Dual-Passivation Strategy of Bulk and Surface Enables Highly Efficient and Stable Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) have captured significant interest due to their outstanding stability, cost-effective fabrication process, and good compatibility with flexible and tandem devices. The presence of bulk and surface defects is key factor in PSCs that cause non-radiative recombination and degradation. To improve the efficiency and stability of inverted PSCs, a bulk-to-surface dual-passivation strategy is employed by utilizing Oleylamine Iodide (OAmI) as additives and 4-Fluorobenzylamine Hydroiodide (4-F-PMAI) as surface passivating agents. Utilizing OAmI as bulk passivation can enhance the crystallinity of perovskite films and reduce lattice defects. Meanwhile, 4-F-PMAI further suppresses non-radiative recombination and reduces open-circuit voltage (VOC) loss through bidentate anchoring. Consequently, the dual-passivation strategy significantly enhances device performance, boosting the power conversion efficiency (PCE) of PSCs to 24.26%, with a VOC of 1.15V. Moreover, the unencapsulated PSCs show excellent long-term stability maintaining over 85% and 90% of the initial efficiency under 85°C thermal annealing in N2 for 1000 hours and after storage in ambient conditions (RH: 30 ± 5%) for 1000 hours.

Effect of Deformed Prior Austenite Characteristics on Reverse Phase Transformation and Deformation Behavior of High-Strength Medium-Mn Steel.

In this study, microstructure evolution during prior austenite decomposition and reverse phase transformation processes was revealed in a high-strength medium-Mn steel. Furthermore, the relationship between deformed prior austenite characteristics and deformation behavior was studied. The results indicated that the recovery and recrystallization of the deformed prior austenite were significantly inhibited during hot rolling in the non-recrystallized zone, the grain size was obviously refined along the normal direction (ND), and that the strain hardening of prior austenite via hot deformation could increase the resistance of shear transformation, resulting in the preservation of high-density lattice defects in the quenched martensite matrix. Before the nucleation of intercritical austenite, the dislocation and grain boundary can provide fast diffusion paths for C and Mn, and the enrichment of C and Mn before intercritical austenite formation can reduce the critical temperature of ferrite/austenite transformation. The nucleated sites and driving force for intercritical austenite were strongly increased by rolling in the non-recrystallization region. The resistance of crack propagation was found to be enhanced by the sustained transformation-induced plasticity (TRIP) effect (via retained austenite with different stability) and for the laminated microstructure, the optimum properties were obtained as being a combination of yield strength of 748 MPa, tensile strength of 952 MPa, and total elongation of 26.2%.

Establishing Non-Stoichiometric Ti4O7 Assisted Asymmetrical C-C Coupling for Highly Energy-Efficient Electroreduction of Carbon Monoxide.

Exploring an appropriate support material for Cu-based electrocatalyst is conducive for stably producing multi-carbon chemicals from electroreduction of carbon monoxide. However, the insufficient metal-support adaptability and low conductivity of the support would hinder the C-C coupling capacity and energy efficiency. Herein, non-stoichiometric Ti4O7 was incorporated into Cu electrocatalysts (Cu-Ti4O7), and served as a highly conductive and stable support for highly energy-efficient electrochemical conversion of CO. The abundant oxygen vacancies originated from ordered lattice defects in Ti4O7 facilitate the water dissociation and the CO adsorption to accelerate the hydrogenation to *COH. The highly adaptable metal-support interface of Cu-Ti4O7 enables a direct asymmetrical C-C coupling between *CO on Cu and *COH on Ti4O7, which significantly lowers the reaction energy barrier for C2+ products formation. Additionally, the excellent electroconductivity of Ti4O7 benefits the reaction charge transfer through robust Cu/Ti4O7 interface for minimizing the energy loss. Thus, the optimized 20Cu-Ti4O7 catalyst exhibits an impressive selectivity of 96.4 % and ultrahigh energy efficiency of 45.1 % for multi-carbon products, along with a remarkable partial current density of 432.6 mA cm-2. Our study underscores a novel C-C coupling strategy between Cu and the support material, advancing the development of Cu-supported catalysts for highly efficient electroreduction of carbon monoxide.

Establishing Non‐Stoichiometric Ti4O7 Assisted Asymmetrical C−C Coupling for Highly Energy‐Efficient Electroreduction of Carbon Monoxide

AbstractExploring an appropriate support material for Cu‐based electrocatalyst is conducive for stably producing multi‐carbon chemicals from electroreduction of carbon monoxide. However, the insufficient metal‐support adaptability and low conductivity of the support would hinder the C−C coupling capacity and energy efficiency. Herein, non‐stoichiometric Ti4O7 was incorporated into Cu electrocatalysts (Cu−Ti4O7), and served as a highly conductive and stable support for highly energy‐efficient electrochemical conversion of CO. The abundant oxygen vacancies originated from ordered lattice defects in Ti4O7 facilitate the water dissociation and the CO adsorption to accelerate the hydrogenation to *COH. The highly adaptable metal‐support interface of Cu−Ti4O7 enables a direct asymmetrical C−C coupling between *CO on Cu and *COH on Ti4O7, which significantly lowers the reaction energy barrier for C2+ products formation. Additionally, the excellent electroconductivity of Ti4O7 benefits the reaction charge transfer through robust Cu/Ti4O7 interface for minimizing the energy loss. Thus, the optimized 20Cu−Ti4O7 catalyst exhibits an impressive selectivity of 96.4 % and ultrahigh energy efficiency of 45.1 % for multi‐carbon products, along with a remarkable partial current density of 432.6 mA cm−2. Our study underscores a novel C−C coupling strategy between Cu and the support material, advancing the development of Cu‐supported catalysts for highly efficient electroreduction of carbon monoxide.

Memristor Array Based on Wafer-Scale 2D HfS2 for Dual-Mode Physically Unclonable Functions.

Conventional Si-based physically unclonable functions (PUFs) take advantage of the unique variations in the fabrication processes. However, these PUFs are hindered by limited entropy sources and susceptibility to noise interference. Here we present a memristive device based on wafer-scale (2-in.) two-dimensional (2D) hafnium disulfide (HfS2) grown by molecular beam epitaxy (MBE). The polycrystalline HfS2 thin film can offer enhanced entropy sources for PUF applications, such as lattice defects, which can facilitate the random formation of conductive filaments and result in significant device-to-device (D2D) variations. Our proposed PUF design seamlessly integrates two distinct operating modes within a single circuit module. First, a reconfigurable and highly secure mode 1, and second, an ultrareliable mode 2, both with near-ideal Entropy (∼1.0), normalized Hamming distance (∼0.5) and correlation coefficient (∼0.0). Additionally, a predictive Fourier regression model further confirms the unpredictable nature of our dual-mode PUF, with an average prediction accuracy of ∼50%.

Reduction in Temperature-Dependent Fiber-Optic Gyroscope Bias Drift by Using Multifunctional Integrated Optical Chip Fabricated on Pre-Annealed LiNbO3

The refractive index change obtained after annealed proton exchange (APE) in lithium niobate (LiNbO3) crystals depends on both the proton exchange process carried out in hot acid and the structure of the crystals. In devices produced by the APE method, dislocations and lattice defects within the crystal structure are considered to be primary contributors to refractive index discontinuities and waveguide instability. In this study, the effects of pre-annealing LiNbO3 crystals at 500 °C on multifunctional integrated optical chips (MIOCs) were investigated through interferometric fiber-optic gyroscope (IFOG) system-level tests. It was observed that the pre-annealing process resulted in an improvement in the optical throughput of MIOCs (from %34 to %51) and the temperature-dependent bias drift stability of the IFOG (from 0.031–0.038°/h to 0.012–0.019°/h). The angle random walk (ARW) was measured as 0.0056 deg/√h.

Characterization of HZO Films Fabricated by Co-Plasma Atomic Layer Deposition for Ferroelectric Memory Applications.

Plasma-enhanced atomic layer deposition (ALD) is a common method for fabricating Hf0.5Zr0.5O2 (HZO) ferroelectric thin films that can be performed using direct-plasma (DP) and remote-plasma (RP) methods. This study proposed co-plasma ALD (CPALD), where DPALD and RPALD are applied simultaneously. HZO films fabricated using this method showed wake-up-free polarization properties, no anti-ferroelectricity, and high fatigue endurance when DPALD and RPALD started simultaneously. To minimize defects in the film that could negatively affect the low polarization properties and fatigue endurance, the direct plasma power was reduced to 75 W. Thus, excellent fatigue endurance for at least 109 cycles was obtained under a high total remanent polarization of 47.3 μC/cm2 and an applied voltage of 2.5 V. X-ray photoelectron spectroscopy and transmission electron microscopy were used to investigate the mechanisms responsible for these properties. The HZO films fabricated by CPALD contained few lattice defects (such as nonstoichiometric hafnium, nonlattice oxygen, and residual carbon) and no paraelectric phase (m-phase). This was attributed to the low-carbon residuals in the film, as high-energy activated radicals were supplied by the adsorbed precursors during film formation. This facilitated a smooth transition to the o-phase during heat treatment, which possessed ferroelectric properties.

Serrated Flow Behavior in Commercial 5019 Aluminum Alloy

Serrated flow effects are visible on a metal surface even after coating. Thus, they are undesirable to manufacturers and product users. To meet the expectations of the industry, research on the conditions for serrated flow occurrence in 5019 aluminum alloy was carried out and the results were collected in the current paper. Thus, the influence of the alloy initial microstructure due to different tempers as well as plastic deformation conditions, i.e., strain rate and temperature, on the alloy stress–strain behavior was determined. Two tempers were considered: the as-fabricated F-temper and the W-temper (i.e., quenched in water after annealing at 500 °C). The synergic influence of these tempers and their tensile test conditions on the serration behavior of the stress–strain curves, i.e., the stress drop and reloading time, were also determined and categorized. Structural and X-ray diffraction studies rationalized the stress–strain characteristics according to dynamic strain aging models with positron annihilation lifetime spectroscopy providing insight into the role of lattice defects (i.e., dislocations and vacancies). The map of the serrated flow domain allowed us to obtain the activation energy of the onset of the Portevin–Le Chatelier effect equal to 56 kJ/mol. It is close to the activation energy for the pipe diffusion mechanism, obtained by applying the model formulated originally for Type B stress serration.

Synthesis of Nd2Sn2O7 pyrochlore with different lattice disorder degrees and oxygen vacancy contents

In this study, a series of Nd2Sn2O7 pyrochlores with different lattice disorder degrees and oxygen vacancy contents were prepared via simple methods, including the sol–gel (SG) technique, glycine–nitrate combustion (GNC), coprecipitation (CP), and the hydrothermal (HT) method. Raman spectroscopy proved the most effective in identifying the lattice disorder degree and lattice defects of the pyrochlore-type composite oxides, followed by XRD, with FTIR spectroscopy as the least sensitive technique. For pure phase Nd2Sn2O7, the content of oxygen vacancies and adsorbed oxygen species follow the sequence CP > GNC > SG, which is well consistent with the lattice disorder degrees. This is because that the higher the lattice disorder of Nd2Sn2O7 pyrochlore, the weaker the Sn-O bond, making it easier to break and form oxygen vacancies. Although the HT sample exhibits the lowest disorder degree, its synergistic effect with residual SnO2 on the surface is beneficial for further enriching oxygen vacancies.

Dynamic deformation and fracture of brass: Experiments and dislocation-based model

In this work, we perform a comprehensive study of the dynamic deformation and fracture of brass, including Taylor tests with classical and profiled cylinders and ball throwing experiments reaching the strain rates of about (0.1−1)/μs, as well as atomistic and continuum-level numerical modeling. Molecular dynamics (MD) simulations are used to construct the equation of state (EOS) of brass and to study its fracture characteristics at shear deformation under negative pressure. An original model of fracture under combined tensile-shear loading is formulated, which takes into account both the accumulation of empty volume in the process of lattice loosening due to the lattice defect production in the course of plastic deformation and further mechanical growth of voids controlled by the dislocation plasticity. This atomic-scale model is transmitted to the macroscopic experiment-scale level and embedded into 3D dislocation plasticity model to describe the dynamic deformation and fracture of brass using the numerical scheme of smoothed particle hydrodynamics (SPH). A part of experimental data is used to find the optimal parameters of the dislocation plasticity model by means of the Bayesian global optimization method accelerated with the help of artificial-neural-network (ANN)-based emulator of the 3D model. Another part of experimental data is used to fit the fracture model parameter. The remaining experimental data, which are not used in the parameterization, are applied to verify the parameterized model. The developed physical-based model provides correct and meaningful description of the dynamic deformation and fracture of brass, while the developed formalized approach to its parameterization opens a way to wider use of this type of models in the engineering applications, including studies on dynamic performance and high-speed processing technologies.

Zn interlayer-induced modifications in interfacial structure and fracture behavior of Cyclic Hot-Pressed Mg/Al laminated composites

In this study, a new type of cyclic hot pressing technology was used to prepare magnesium-aluminum composites. In order to further simplify the process, the active zinc interlayer was introduced, and the interfacial bonding strength of Mg/Al LMCs was increased by 43.25%. The traditional Mg/Al LMCs interface is mainly composed of Mg-Al IMCs (β-Mg2Al3 and γ-Mg17Al12), in which the highly regular HCP-β phase leads to brittle fracture of the material. After adding zinc layer, the interface of the composites mainly presents Al-SS, η (MgZn2) and Mg-SS phases. During the preparation process, the solid solution treatment and aging treatment occurred at the composite interface, and a chain GPII zone was formed at the interface between Al-SS and η phase. This region is mainly composed of structurally unstable η′(Al-Mg-Zn), resulting in the GP II band becoming a region rich in lattice defects and a fracture source of the composite.

Promoting transparency: Defect-driven sintering of Gd2Zr2O7 ceramics for advanced radiation applications

Transparent Gd2Zr2O7 (GZO) ceramics show significant potential for radiation detection and nuclear energy applications. However, scalable production through cost-effective solid-state vacuum sintering is challenging due to the material's high melting point and low thermal conductivity. This study introduces a novel approach by incorporating excess Gd to increase lattice defects, such as cation disorder and oxygen vacancies, which have low formation energy. This strategy lowers the energy barrier for ion diffusion, enhances material migration during sintering, and promotes the elimination of residual pores, leading to high densification. We examined the densification behavior of GZO compositions with varying Gd content (Gd1.8Zr2O6.7 to Gd2.5Zr2O7.75) during vacuum sintering at 1450°C to 1900°C, focusing on phase transformation, grain growth, and pore elimination. Notably, the optimal sample achieved 78.3 % transmittance, approaching the theoretical maximum. These findings offer a promising route for the large-scale production and commercialization of transparent GZO ceramics for advanced radiation applications.

Enhanced flux pinning properties of Ga2O3: YBCO nanocomposite superconductor

The effect of adding various concentrations (0.1–0.5 wt%) of Ga2O3 nanorods (NRs) on structural, electrical, magnetic, and flux pinning properties of the YBa2Cu O7-δ (YBCO) superconductor is studied. The critical current density (Jc) and flux pinning force (Fp) values are found to enhance significantly, and the nanocomposite sample with x = 0.2 wt% shows the maximum enhancement among the samples under study. At 4 K, the maximum value of Jc (Jcmax) and Fp (Fpmax) for the 0.2 wt% sample are ∼ 2.87 and 3 times higher and at 65 K, these increments are ∼ 3.54 and 3.4 times, as compared to pure YBCO respectively. Moreover, the Jc value for the composite samples has a lower decay with increasing temperature than the pure YBCO samples. The enhanced superconducting properties of the xGa2O3: YBCO can be attributed to the lattice defects induced by Ga2O3 NRs, which act as effective pinning centers.

Kinetics of electromigration mass transfer in micro- and nanoelectronics interface elements depending on the strength of thin-film junctions

The theoretical model proposed earlier by the authors, which describes the interrelation of strength and electromigration (diffusion) properties of interfaces formed by joined materials, has been perfected and extended. Within the framework of the developed model, a linear relationship between the values of the work of reversible interface separation Wa and the activation energy of electromigration in the interface HEM was established. The coefficients of the obtained relation are estimated and compared with experimental data on the study of electromigration in a copper conductors covered with protective dielectrics. Using also the model developed earlier by the authors, which describes the dependence of the value on the concentrations of non-equilibrium lattice defects in the volumes of joined materials, a number of effects due to the influence of such defects on the processes caused by electromigration have been predicted and investigated. In the paper we obtained that by introducing non-equilibrium lattice defects in the volumes of bonded materials in the form of atomic impurities of interstition or substitution it is possible to effectively influence the characteristics of electromigration instability of the shape of the interlayer interface. For the introduction impurities, quantitative analytical estimates of the impurity concentration necessary for a significant change (both increase and decrease) in the characteristic rise time of the instability of the shape of the initially flat interface have been obtained.