Lattice Dislocations Research Articles

Synergistically optimized electron and phonon transport in high-performance copper sulfides thermoelectric materials via one-pot modulation

Optimizing thermoelectric conversion efficiency requires the compromise of electrical and thermal properties of materials, which are hard to simultaneously improve due to the strong coupling of carrier and phonon transport. Herein, a one-pot approach realizing simultaneous second phase and Cu vacancies modulation is proposed, which is effective in synergistically optimizing thermoelectric performance in copper sulfides. Multiple lattice defects, including nanoprecipitates, dislocations, and nanopores are produced by adding a refined ratio of Sn and Se. Phonon transport is significantly suppressed by multiple mechanisms. An ultralow lattice thermal conductivity is therefore obtained. Furthermore, extra Se is added in the copper sulfide for optimizing electrical transport properties by inducing generating Cu vacancies. Ultimately, an excellent figure of merit of ~1.6 at 873 K is realized in the Cu1.992SSe0.016(Cu2SnSe4)0.004 bulk sample. The simple strategy of inducing compositional and structural modulation for improving thermoelectric parameters promotes low-cost high-performance copper sulfides as alternatives in thermoelectric applications.

Cooperative effect of grain size and cryogenic temperature on deformation behavior and mechanism of commercial pure Al sheets

In this paper, the effect of grain sizes on mechanical properties and microstructure evolution of pure Al sheet at cryogenic temperatures were studied by uniaxial tensile tests and microstructure observations. The results show a great exciting strain hardening ability for the sheet with ultra-fine grain (UFG) at cryogenic temperature, and the cooperative increasing in strength and ductility of pure Al at cryogenic temperatures become more and more prominent with the decrease of grain size. With the decrease of grain size, the increase of yield strength by decreasing temperature becomes more dramatic. The mechanism of increase in yield strength at cryogenic temperatures is attributed to the contribution of three temperature-dependent factors: grain boundary strengthening, lattice friction resistance and dislocation strengthening, in which grain boundary strengthening plays a dominant role. The grain size dependence of the strain hardening ability increased with decreasing temperature is mainly related to the inhibition of cross-slip in the grain interiors and the dislocation annihilation at grain boundaries, so that dislocation can effectively multiply and accumulate, which is totally different from the strain softening and poor plasticity of UFG pure Al at room temperature (RT) caused by the enhanced dislocation annihilation. As a result, the trade-off relationship between the strength and plasticity caused by different grain sizes is significantly weakened at cryogenic temperatures, which provides a very potential method for the complex parts forming of UFG sheets and mechanical properties improvement.

Dislocation Majorana bound states in iron-based superconductors

We show that lattice dislocations of topological iron-based superconductors such as FeTe1−xSex will intrinsically trap non-Abelian Majorana quasiparticles, in the absence of any external magnetic field. Our theory is motivated by the recent experimental observations of normal-state weak topology and surface magnetism that coexist with superconductivity in FeTe1−xSex, the combination of which naturally achieves an emergent second-order topological superconductivity in a two-dimensional subsystem spanned by screw or edge dislocations. This exemplifies a new embedded higher-order topological phase in class D, where Majorana zero modes appear around the “corners” of a low-dimensional embedded subsystem, instead of those of the full crystal. A nested domain wall theory is developed to understand the origin of these defect Majorana zero modes. When the surface magnetism is absent, we further find that s± pairing symmetry itself is capable of inducing a different type of class-DIII embedded higher-order topology with defect-bound Majorana Kramers pairs. We also provide detailed discussions on the real-world material candidates for our proposals, including FeTe1−xSex, LiFeAs, β-PdBi2, and heterostructures of bismuth, etc. Our work establishes lattice defects as a new venue to achieve high-temperature topological quantum information processing.

Gas-sensing properties of p-type of nitrogen-doped ZnO nanorods prepared by deep cryogenic treatment

This study developed p-type nitrogen-doped zinc oxide nanorods (NZO NRs) using a chemical bath deposition and deep cryogenic treatment. These NRs were employed to create the device structure of metal-oxide-metal (MSM) and p-n junction for a volatile organic compound gas sensor. Deep cryogenic treatment is the process of immersing ZnO NRs in liquid nitrogen to achieve NZO NRs. SEM results show that the morphology of NZO changes from hexagonal to nib shapes. XRD and TEM results demonstrate that the peak of (002) shifts, and lattice dislocation was observed in NZO specimen. XPS and EDS analysis proved that the N atoms were successfully doped into ZnO. Optical analysis showed the lower band gap and a broader absorption region of NZO NRs. The doping mechanism of NZO is deduced as polar molecules distributed on the high-surface area of ZnO NRs, with iron playing a catalytic role. The MSM structure of the p-type NZO gas sensor, exhibiting high response, lifetime and selectivity, was verified at room temperature. The gas sensor with a p-n junction structure exhibits a faster response time to ethanol.

High-pressure phase transformations and lattice distortions in industrial AISI 1070 steel: Insights from Debye-Scherrer ring integration

In this study, the behavior of the industrially prominent AISI 1070 pearlitic steel under pressures up to 35 GPa was meticulously explored. Leveraging the 1D integration patterns from the Debye-Scherrer rings, we introduced a groundbreaking method to quantify dislocation densities, providing a novel lens to understand lattice distortions in such widely-used steels. At 5 GPa, the decomposition of cementite became evident, corroborated by changes in lattice parameters and dislocation densities. As the pressure neared to 10 GPa, the emergence of Hägg carbide was observed. The hallmark discovery was the phase transition from BCC to HCP around 20 GPa. This transformation bore witness to further distortions in the HCP structure with mounting pressures. Finally, molecular dynamic simulations revealed a mostly BCC to HCP transformation via an intermediary FCC phase at crystalline defects, elucidating observed orientations and phase transformation pathways.

Preparation and Performance Study of Titanium‐Based Nanocomposites in Selective Laser Melting: Microstructure Regulation and Optimization of Mechanical Properties

This study focuses on exploring the application of selective laser melting (SLM) technology in the preparation of titanium‐based nanocomposite materials. By introducing 0.5 wt% graphene oxide (GO) and 7.0% nanomolybdenum (Mo) powder, an attempt is made to improve the microstructure and mechanical properties of titanium alloy materials. The experimental results indicate that the microstructure of the titanium‐based nanocomposite material undergoes significant crystal refinement and phase transition behavior, suggesting a positive role of introducing nanoreinforcing phases in crystal structure regulation. Simultaneously, the introduction of GO significantly improves the thermal conductivity of the material, contributing to more uniform energy transfer and temperature distribution, thereby optimizing the process control of laser melting. In terms of mechanical performance, through microhardness and tensile performance tests, the microhardness of TC4–0.5GO–7Mo increases by ≈30.8% compared with pure TC4. This strengthening effect is primarily attributed to the uniform distribution of GO and Mo powder in the matrix, effectively hindering lattice slip and dislocation movement, enhancing the hardness and tensile properties of the material. Through a comprehensive analysis of microstructure and mechanical properties, not only the mapping relationship between the microstructure and mechanical properties of titanium‐based nanocomposite materials is clarified but also the strengthening mechanism is revealed.

Improving Properties of Tungsten Oxide Films by Gamma Ray Irradiation

The deposition process and investigation of the physical properties of tungsten trioxide (WO3) thin films before and after gamma irradiation are presented in this paper. The WO3 thin films were deposited, using the pulse laser deposition technique, on glass substrates at laser energies of 600mJ and 800mJ. After deposition, the samples were gamma irradiated with Co60. The structural and optical properties of polycrystalline WO3 thin films are presented and discussed before and after 5kGy gamma irradiation at the two laser energies. X-ray diffraction spectra revealed that all the films consisted of WO3 crystallized in the triclinic form; the dislocation density and lattice strain increased with the absorbed dosage of gamma irradiation. The optical constants, the average diameter and the surface roughness of the WO3 films were calculated before and after gamma irradiation and for the two laser energies. It was found that the WO3 thin films conductivity increased by γ-irradiated and with the increase of the laser energy.

Effect of Aging Time on Microstructure and Properties of Cold-Rolled Ni-W-Co-Ta Medium–Heavy Alloy

A systematical exploration of the effect of aging time on the microstructure and mechanical properties of cold-rolled Ni-W-Co-Ta medium–heavy alloy with 90% thickness reduction at the aging temperature of 700 °C was performed. The results demonstrate that the volume fraction of the precipitation (Ni4W), which persists under various aging times, increases from 13.7% (2 h) to 28.7% (32 h) with the extension of aging time. Meanwhile, the microstructure after aging treatment is still dominated by dislocation entanglement and dislocation walls, although the degree of lattice distortion and dislocation density attributed to heavy deformation decreases. The maximum tensile strength, yield strength, and microhardness (2286 MPa, 1989 MPa, 766 HV) of the cold-rolled Ni-W-Co-Ta medium–heavy alloy under the 16 h aging treatment at 700 °C are reached, respectively. The ductile–brittle mixed fracture morphology is maintained in the fracture morphology of the medium–heavy alloy before and after aging treatment.

In situ synchrotron investigation of tensile deformation and failure mechanisms in cold spray Cr-coated Zr-alloy system

High energy synchrotron X-ray diffraction in the transmission mode was performed in situ during uniaxial tensile testing to understand the deformation and cracking behavior of cold spray Cr-coated Zr-alloy specimens in both the as-deposited and annealed conditions. The fracture surface of the specimens, examined using scanning electron microscopy, revealed that the Cr coatings in both samples remained strongly adherent to the substrates through the completion of the tensile test. Both elastic and plastic deformation mechanisms during tensile deformation were quantified using detailed X-ray line profile analysis. High dislocation density with a unique distribution of edge and screw fractions and non-zero lattice strain was determined to be present in the cold spray Cr coating due to high strain-rate deformation during cold spray deposition. The annealing treatment reduced both residual lattice strain and dislocation density (with preferentially higher reduction in edge fractions) in the Cr coating. This led to a heterogeneous distribution of dislocation density and character among different grains, that enhanced resistance to crack propagation in the annealed Cr coating. The mechanical properties of the Zr-alloy in both specimens were not significantly altered by the presence of the cold sprayed Cr coating on the surface.

The phase stability of t-ZrO2 realized by grain size at cryogenic temperature in ZrO2/TiO2 composite

In this work, the trade-off between transformation toughening of ZrO2/TiO2 ceramic coatings and low temperature (293.15 K∼203.15 K) was achieved by adjusting the grain size of t-ZrO2 (dt-ZrO2). A negative correlation between dt-ZrO2 and phase transition temperature (Ms) was also established based on strain energy and chemical free energy in ZrO2/TiO2 ceramic coatings. Interestingly, t-ZrO2 grains lost toughening effects when the dt-ZrO2 reaches the critical size (20 nm) even under cooling and stress. This is attributed to the number of dislocations per unit volume increases 1.5 times with the dt-ZrO2 decreases from 40 nm to 20 nm, which aggravates the lattice distortion and dislocation tangle and leads to the fracture toughness increases by 32.5% at 203.15 K. Therefore, the interfacial cohesion of the semi-coherent interface between (011) t-ZrO2 and (110) TiO2 was enhanced and t-ZrO2 was completely stabilized when dt-ZrO2 reaches critical size. This work elucidates the effect of size effect on Ms and provides a reference for transformation toughening of ceramic coatings at cryogenic temperature.

The Construction of a Lattice Image and Dislocation Analysis in High-Resolution Characterizations Based on Diffraction Extinctions.

This paper introduces a method for high-resolution lattice image reconstruction and dislocation analysis based on diffraction extinction. The approach primarily involves locating extinction spots in the Fourier transform spectrum (reciprocal space) and constructing corresponding diffraction wave functions. By the coherent combination of diffraction and transmission waves, the lattice image of the extinction planes is reconstructed. This lattice image is then used for dislocation localization, enabling the observation and analysis of crystal planes that exhibit electron diffraction extinction effects and atomic jump arrangements during high-resolution transmission electron microscopy (HRTEM) characterization. Furthermore, due to the method's effectiveness in localizing dislocations, it offers a unique advantage when analyzing high-resolution images with relatively poor quality. The feasibility of this method is theoretically demonstrated in this paper. Additionally, the method was successfully applied to observed edge dislocations, such as 1/6[211-], 1/6[2-11-], and 1/2[01-1], which are not easily observable in conventional HRTEM characterization processes, in electro-deposited Cu thin films. The Burgers vectors were determined. Moreover, this paper also attempted to observe screw dislocations that are challenging to observe in high-resolution transmission electron microscopy. By shifting a pair of diffraction extinction spots and superimposing the reconstructed images before and after the shift, screw dislocations with a Burgers vector of 1/2[011-] were successfully observed in electro-deposited Cu thin films.

Cold Sintering Mediated Engineering of Polycrystalline SnSe with High Thermoelectric Efficiency.

Despite the attractive thermoelectric properties in single crystals, the fabrication of high-performance polycrystalline SnSe by a cost-effective strategy remains challenging. In this study, we prepare the undoped SnSe ceramic with remarkable thermoelectric efficiency by the combination of a cold sintering process (CSP) and thermal annealing. The high sintering pressure during CSP induces not only highly oriented grains but also a high concentration of lattice dislocations and stacking faults, which leads to large lattice strain that can shorten the phonon relaxation time. Meanwhile, the thermal annealing breaks the highly resistive SnOx layers at grain boundaries, which improves the electrical conductivity and power factor. In addition, the grain growth during annealing further turns the broken SnOx layers into nanoparticles, which further lowers the thermal conductivity by enhanced scattering. As a result, a peak ZT of 1.3 at 890 K and a high average ZT of 0.69 are achieved in the polycrystalline SnSe, suggesting great potential in mid-temperature power generation. This work may pave the way for the mass production of SnSe-based ceramics for thermoelectric devices.

The effects of twist angle and loading mode on the deformation behavior of bicrystal copper

The effects of twist angle and loading mode on deformation behavior of bicrystal Cu containing symmetric twist grain boundary are investigated by molecular dynamics. Grain boundary dislocation network changes from square-like to ring-like with increasing twist angle. Tensile strength under loading parallel to grain boundary is higher than that under perpendicular loading to grain boundary for the same model, and the larger twist angle is, the larger difference under two loading modes is. Under perpendicular and parallel loadings, initial plastic yield of bicrystal Cu with low angle is triggered by slipping of grain boundary partial dislocations, which results in almost complete dissociation of grain boundary and formation of pillar-like voids inside grains. However, initial plastic yields of bicrystal Cu with higher angle are triggered by explosive collective slipping of short grain boundary partial dislocation and nucleating of new lattice dislocations on grain boundary, respectively, which result in direct splitting of grain boundary and formation of sphere-like voids, respectively. The calculated increase rates of partial dislocation number increase with increasing twist angle, but the increase amplitude is significantly larger under parallel loading. In later stage, void volume of each model is almost the same, but void surface area is significantly different.

The effects of Mn doping on structural, morphological, and optical properties of hydrothermally synthesized h-MoO3 nanorods

Pure and Mn-doped h-MoO3 nanorods with varying doping concentrations (1, 3, 5 M%) have been synthesized via the hydrothermal method. Subsequently, the impacts of Mn incorporation on the microstructural and optical properties of the synthesized nanorods have been examined. The X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) have confirmed the metastable hexagonal phase (h-MoO3) and rod-type morphology, respectively. To explore various crystallographic features, such as crystallite size and lattice strain, the Scherrer formula, Williamson-Hall (W–H), and Halder-Wagner (H–W) techniques were used. In addition, the dislocation density, lattice parameters, and unit cell volume have been evaluated in conjunction with XRD analysis by Rietveld refinement. The optical bandgap was estimated from UV–vis spectroscopy utilizing the Kubelka-Munk (K-M) function and the Tauc relation. The estimated bandgap values ranged from 3.05 to 3.09 eV for the K-M function and 2.92–2.98 eV for the Tauc relation. The optical bandgap increased as the concentration of Mn increased to 3 M% and then decreased. Both approaches showed analogous optical bandgap variation.

Performance of a deep convolutional neural network to classify crystal structures using selected area electron beam diffraction patterns containing lattice defect information.

A deep convolutional neural network (DCNN) architecture ResNet has been tested to verify its ability to handle selected area electron diffraction pattern (SADP) datasets carrying information on lattice defects including strains, thermal lattice vibrations, point defects, dislocations, and twin boundaries. The disordered states of the crystal lattices in the presence of these defects were predicted by ab initio molecular dynamics simulations, first principles geometry optimizations, and lattice manipulation operations in an effort to establish a possible dataset augmentation strategy for the improvement of classification performance of the ResNet. Using the disordered lattice information originating from the defects, test dataset SADPs were generated by simulating electron diffraction in transmission electron microscopy. The ResNet, pre-trained using SADPs from defect-free materials, showed decreasing but acceptable classification accuracies with increasing degrees of lattice disorder regarding the lattice vibrations and point defects. When tested using the diffraction patterns for strained lattices, the ResNet responded to the changing lattice symmetry when strain levels are relatively high suggesting that it has capability to discern different symmetries induced by large strains. However, the ResNet failed to recognize lattice structure when dislocations and twin boundaries were considered. It is suggested that DCNN architectures be trained over various scenarios including changes in the image feature characteristics in the diffraction patterns related to defects in future developments for improved general classification performances.

Rapid carbothermal shocking fabrication of iron-incorporated molybdenum oxide with heterogeneous spin states for enhanced overall water/seawater splitting.

Molybdenum dioxide (MoO2) has been considered as a promising hydrogen evolution reaction (HER) electrocatalyst. However, the active sites are mainly located at the edges, resulting in few active sites and poor activity in the HER. Herein, we first reported on an efficient strategy to incorporate Fe into MoO2 nanosheets on Ni foam (Fe-MoO2/NF) using a rapid carbothermal shocking method (820 °C for 127 s). Notably, the different spin states between Fe and Mo atoms could lead to rich lattice dislocations in Fe-MoO2/NF, exposing abundant oxygen vacancies and the low-oxidation-state of Mo sites during the rapid Joule heating process. As tested, the catalyst exhibited superior activity with ultralow overpotentials (HER: 17 mV@10 mA cm-2; oxygen evolution reaction (OER): 310 mV@50 mA cm-2) and high OER selectivity in alkaline seawater splitting. Meanwhile, this catalyst was equipped in a home-made anion exchange membrane (AEM) seawater electrolyzer, which achieved a low energy consumption (5.5 kW h m-3). More importantly, Fe-MoO2/NF also coupled very well with a solar-driven electrolytic system and turned out a solar-to-hydrogen (STH) efficiency of 13.5%. Theoretical results also demonstrated that Fe incorporated and abundant oxygen vacancies in MoO2 can distort the distance of the Mo-O bonds and regulate the electronic structure, thus optimizing the binding energy of H*/OOH* adsorption. This method can be extended to other heterogeneous spin states in MoO2-based catalysts (e.g. Ni-MoO2/NF, Co-MoO2/NF) for seawater splitting, and provide a simple, efficient and universal strategy to prepare highly-efficient MoO2-based electrocatalysts.

Crystallography, twinning elements and interface structure of hierarchical lamellar γ type martensite in Ni-Mn-Ga alloys

Microstructural features of lamellar γ in as-cast Ni54Mn28+xGa18–x (0, 4, 7, 9, 11, and 15) alloys are investigated. With increases of Mn content, γ grain size increases from one to hundreds of micrometers. In small grain, {011} primary microtwins with tetragonal crystal structure are found. The twinning elements are K1 = (011), η1 = [011¯], K2 = (011¯), η2 = [011], and s = 0.169. In medium-sized grain, it comprises of six groups of self-accommodated variants, each of which contains {011} secondary nanotwins. Within a single group, there are four variants, designated as A, B, C and D. The A-C and A-B interfaces are nearly straight, the A-D interface is zigzag, and they have a few lattice dislocations. In the vicinity of γ grain, tertiary nanotwins of non-modulated (NM) martensite arise. In large grain, a series of {111} twin intersections occurs within γ micro-lamella, forming configurations resembling self-accommodated NM martensite. Orientation relationship between lamellar γ and NM martensite is determined. Owing to the microstructural similarity to NM martensite, the lamellar γ is defined as a new type of martensite. The variation in grain size affects the hierarchical twin microstructure of γ type and NM martensites. Occurrence of such phenomenon may mainly source from their different stresses required to activate higher-order twinning. Influence of γ on the mechanical property of Ni-Mn-Ga is discussed.

Revealing the Accelerated Capacity Decay of a High‐Voltage LiCoO2 upon Harsh Charging Procedure

AbstractIn practical applications, LiCoO2 (LCO) cathode is usually charged with a constant current plus constant voltage (CC+CV) procedure to obtain higher capacity delivery. However, the harsh condition upon CC+CV procedure causes the accelerated capacity decay of LCO. Herein, the fading mechanism of LCO cycling upon CC+CV procedure at 4.6 V versus Li/Li+ is first revealed. Comparing with a pure CC charging, the accelerated capacity decay of LCO upon CC+CV procedure is attributed to both the bulk and surface structure damages: i) the CV charging triggers more H1‐3 phase separation, leading to the generation of lattice dislocations, curved Co‐O layers, and ultimately the bulk microcracks inside the LCO particles; ii) upon cycle, the CV charging causes more side reactions and more surface structure collapse issues, including forming thick surface phase transition layer (PTL), causing more Co dissolution, forming thick and loose CEI layer, etc., which seriously increases the charge transfer resistance and reduces the interface Li+ transport kinetics. This work provides a new insight into the fading mechanism, and shows a new pathway for designing more advanced LCO cathodes.

Optimization of the thermoelectric properties of Nb-doped Bi2S3 via high pressure and high temperature

Bi2S3 is considered a promising n-type thermoelectric (TE) material due to its inherent extremely low thermal conductivity and earth-abundant elements. Herein, we have successfully synthesized a series of Nb-doped Bi2S3 (Bi2-xNbxS3, x = 0, 0.01, 0.02, 0.03) bulk materials by combining mechanical alloying (MA) method and high pressure and high temperature (HPHT) technology. The enhanced electrical transport properties of the Nb-doped Bi2S3 samples is derived from the collaborative optimization of carrier concentration and effective mass, which indicated that the Nb dopants acted as donors. In addition, differences in the direction of the lattice fringes were observed in the samples, and a large number of lattice distortions and dislocation defects occurred, which significantly reduced the lattice thermal conductivity of the Bi2S3 material. Consequently, a peak zT of 0.22 was achieved for the Bi1.98Nb0.02S3 sample at 543 K, which is 120% higher than that of pure Bi2S3.

Three-dimensional atomic structure and local chemical order of medium- and high-entropy nanoalloys.

Medium- and high-entropy alloys (M/HEAs) mix several principal elements with near-equiatomic composition and represent a model-shift strategy for designing previously unknown materials in metallurgy1-8, catalysis9-14 and other fields15-18. One of the core hypotheses of M/HEAs is lattice distortion5,19,20, which has been investigated by different numerical and experimental techniques21-26. However, determining the three-dimensional (3D) lattice distortion in M/HEAs remains a challenge. Moreover, the presumed random elemental mixing in M/HEAs has been questioned by X-ray and neutron studies27, atomistic simulations28-30, energy dispersive spectroscopy31,32 and electron diffraction33,34, which suggest the existence of local chemical order in M/HEAs. However, direct experimental observation of the 3D local chemical order has been difficult because energy dispersive spectroscopy integrates the composition of atomic columns along the zone axes7,32,34 and diffuse electron reflections may originate from planar defects instead of local chemical order35. Here we determine the 3D atomic positions of M/HEA nanoparticles using atomic electron tomography36 and quantitatively characterize the local lattice distortion, strain tensor, twin boundaries, dislocation cores and chemical short-range order (CSRO). We find that the high-entropy alloys have larger local lattice distortion and more heterogeneous strain than the medium-entropy alloys and that strain is correlated to CSRO. We also observe CSRO-mediated twinning in the medium-entropy alloys, that is, twinning occurs in energetically unfavoured CSRO regions but not in energetically favoured CSRO ones, which represents,to our knowledge, the first experimental observation of correlating local chemical order with structural defects in any material. We expect that this work will not only expand our fundamental understanding of this important class of materials but also provide the foundation for tailoring M/HEA properties through engineering lattice distortion and local chemical order.