Parallel Grain Research Articles

Probing Nanoscale Charge Transport Mechanisms in Quasi-2D Halide Perovskites for Photovoltaic Applications.

Quasi-2D layered halide perovskites (quasi-2DLPs) have emerged as promising materials for photovoltaic (PV) applications owing to their advantageous bandgap for absorbing visible light and the improved stability they enable. Their charge transport mechanism is heavily influenced by the grain orientation of their crystals as well as their nanostructures, such as grain boundaries (GBs) and edge states─the formation of which is inevitable in polycrystalline quasi-2DLP thin films. Despite their importance, the impact of these features on charge transport remains unexplored. In this study, we conduct a detailed investigation on polycrystalline quasi-2DLP thin films and devices, carefully analyzing how grain orientation and nanostructures influence charge transport. Employing nondestructive atomic force microscopy (AFM) topography, along with transient absorption spectroscopy (TAS) and grazing-incidence wide-angle X-ray scattering (GIWAXS), we obtained significant insights regarding the phase purity, crystallographic information, and morphologies of these films. Moreover, our systematic investigation using AFM-based techniques, including Kelvin probe force microscopy (KPFM) and conductive AFM (c-AFM), elucidates the roles played by GBs and edge states in shaping charge transport behavior. In particular, the local band structure along the GBs and edge states within both vertical and parallel grains was found to selectively repel electrons and holes, thus facilitating charge carrier separation. These findings provide perspectives for the development of high-performance quasi-2DLP PV devices and highlight potential approaches that can leverage the intrinsic properties of quasi-2DLPs to advance the performance of perovskite solar cells.

Mitigation of interfacial dielectric loss in aluminum-on-silicon superconducting qubits

We demonstrate aluminum-on-silicon planar transmon qubits with time-averaged T1 energy relaxation times of up to 270 μs, corresponding to Q = 5 million, and a highest observed value of 501 μs. Through materials analysis techniques and numerical simulations we investigate the dominant source of energy loss, and devise and demonstrate a strategy toward its mitigation. Growing aluminum films thicker than 300 nm reduces the presence of oxide, a known host of defects, near the substrate-metal interface, as confirmed by time-of-flight secondary ion mass spectrometry. A loss analysis of coplanar waveguide resonators shows that this results in a reduction of dielectric loss due to two-level system defects. The correlation between the enhanced performance of our devices and the film thickness is due to the aluminum growth in columnar structures of parallel grain boundaries: transmission electron microscopy shows larger grains in the thicker film, and consequently fewer grain boundaries containing oxide near the substrate-metal interface.

Thermoelectric enhancement in perovskite type textured Me0.85TiO3 ceramics by synergistic high-entropy and microstructure manipulations

Enhancing the figure-of-merit (ZT) for thermoelectric ceramics essentially needs strategies that aim to concurrently optimize electron and phonon transport properties to decouple their coupling relationship. This work developed 〈001〉 -textured Me0.85TiO3(Me = La, Sr, Ba, Ca) ceramics (LSBC-T) with a texture fraction of 92 % fabricated by a tape casting process combined with template grain-growth method, in which 10 wt% (001) oriented plate-like SrTiO3 serves as template seed and A-site deficient high-entropy (La0.25Sr0.25Ba0.25Ca0.25)0.85TiO3 composite was used as matrix material. A peak ZT of 0.27 was attained at 1073 K in the sample parallel to the tape casting direction which was twice the ZT = 0.13 of the non-textured sample. Quantitative analysis of atomic displacement disorder of A-site elements would provide an atomistic-scale understanding of grain orientation evolution with high texture degree and the low thermal conductivity of 1.79 W/(m‧K) at 1073 K. The complex multi-scale defects consist of cation and oxygen vacancies, edge dislocations, parallel grain boundaries, phase interfaces, nanoscale metal/inorganic coexisting clusters, and metal Bi sandwich layer, which act as additional phonon scattering centers while affecting carrier transport, covering all frequency phonons (100 GHz-15 THz). In addition, multi-scale parallel interfaces, including atomic-scale crystal (00l) plane of SrTiO3 seed, nano-scale “core-shell” interface parallel to the (00l) plane, metal Bi particle forming a sandwich layer in SrTiO3 seed, and “brick-wall” textured grain boundaries, make the electrical and thermal conductivity exhibiting obvious anisotropy in this LSBC-T high-entropy textured ceramics. By utilizing texture engineering in high-entropy systems, this work provides a theoretical foundation and technical support for the advancement of microstructure manipulations to reduce the inherent lattice thermal conductivity, achieve electrical and thermal conductivity anisotropy to decouple the electron–phonon coupling relationship, and thereby enhance thermoelectric properties.

Alternative processing routes on CsH2PO4 proton conductors: Cold sintering and ball-milling routes

Cesium dihydrogen phosphate (CsH2PO4) holds great potential as electrolyte for intermediate-temperature fuel cells and electrochemical devices due to its high proton conductivity (≥10−2 S/cm). This study reports on the variation of the microstructure of CsH2PO4 and its effect on its electrical and thermal properties, with special attention to the low-temperature conductivity behavior. To manipulate morphology, the particle size was decreased by wet ball-milling, while variations in grain growth were achieved by cold sintering. Above the superprotonic phase transition, the electrical conductivity was effectively independent of the grain size. Nonetheless, at lower temperatures, a brick layer analysis on the impedance data revealed that the conductivity of the monoclinic phase is governed by the conduction pathways along the parallel grain boundaries due to the humidified atmosphere. Overall, we propose two conduction mechanisms that could explain the grain boundary conductivity of these samples, revealing critical links between sample morphology and low-temperature electrical behavior.

Mechanical properties of multi-bolted Glulam connection with slotted-in steel plates

The Bolted Glulam Connection with Slotted-in Steel Plates (BGCSSP) is widely employed in modern timber structures due to its advantages of convenient installation and reliable force transmission. However, the current design methods lack rigorous mechanical derivation and fail to consider various influencing factors comprehensively. Furthermore, designing multiple dowel connections based on the behavior of individual dowels impedes optimization and limits the applicability of design rules. To systematically investigate the failure modes and mechanical characteristics of Multi-bolted Glulam Connection with Slotted-in Steel Plates (MGCSSP), specimens from 12 groups (6 specimens per group) were subjected to parallel grain tensile tests, considering four key influencing factors: bolt quantity, bolt arrangement, bolt diameter, and base material thickness. The experimental results indicate that as the number of bolts increases, the failure transitions from double-hinge failure to single-hinge failure. Additionally, there is an observable upward trend in both initial stiffness and peak load for the same type of specimen as the quantity of bolts increases, accompanied by a decreasing trend in the ductility coefficient. The analysis of experimental results reveals that both the quantity and diameter of bolts impact the initial stiffness and peak load of MGCSSP specimens. Based on experimental observations, dual-parameter calculation models for the initial stiffness and peak load of MGCSSP are proposed. The calculated results of the models align well with experimental data, providing references and convenience for the design of MGCSSP.

Wood utilized for wooden components in ancient buildings of Tingbao Yang’s former residence

Summary A comprehensive analysis was conducted using optical microscopy based on wood anatomy to enhance the preservation of wooden components in Tingbao Yang’s former residence. This study identified wood samples, and statistical examination of wood species, variations in their configuration, physical and mechanical properties, and natural durability were examined. The principles for wood species selection were assessed. Findings indicate that Cunninghamia lanceolata, Pseudotsuga spp., Populus spp. and Ulmus spp. are the primary choices for these wooden components. However, certain portions incorporate Larix sect. Multiseriales, Picea brachytyla, Pinus bungeana, Pinus massoniana, Castanea sp. and Quercus subg. Lepidabalanus, sect. Prinus. Pseudotsuga spp., C. lanceolata, Ulmus spp. and Populus spp. are primarily utilized for wooden columns and melon columns. However, C. lanceolata, Ulmus spp. and Populus spp. possess inadequate parallel grain compressive strength for load-bearing compression wooden components. C. lanceolata and Ulmus spp. are widely utilized in beams, lintels, purlins, and rafters owing to their exceptional bending strength. It was noted that Castanea sp. and Quercus subg. Lepidabalanus, sect. Prinus wood varieties demonstrate superior resistance to rotting and insects compared with other types of wood. The selection of wood species for the ancient buildings of Tingbao Yang’s former residence relies on crucial principles, such as the suitability of wood properties and local selection. This selection process involves analyzing the wood properties, assessing the natural durability of wooden components, and considering the distribution of forest resources in Henan Province.

Threshold and structure of HCP/FCC nucleation in BCC iron under arbitrary triaxial compression: Atomistic simulations

Shear deformation is one of the primary factors determining the threshold of structural transition (ST). It is important to quantitatively express the relationship between shear deformation and the ST threshold for the in-depth development of ST dynamics models. This work used classical molecular dynamics methods to study the effect of shear deformation on the ST in iron by controlling the triaxial ratio of compression. Based on the simulation results, there are significant differences in the microstructure for different loading paths. HCP lamellar twins, HCP-FCC thin twins, and crossed HCP twins embedded with parallel hexahedral FCC grains were all observed, as uniaxial loading transitions to equiaxial loading. The changes in pressure and the softening range of shear stress under different triaxial compressions were revealed. By introducing the strain triaxiality (i.e., the ratio of shear strain to volumetric strain), a general expression of the pressure threshold of ST under high strain rate compression-shear was proposed. In addition, whether the close-packed plane is easily activated under different strain environments was explained based on the results of stacking fault energy.

Grain refinement mechanism in adiabatic shear band of solution treated Ti–10V–2Fe–3Al alloy under high strain rate

The grain refinement mechanism in the adiabatic shear band (ASB) of solution treated Ti–10V–2Fe–3Al alloy was investigated under high strain rates using a split Hopkinson pressure bar and hat-shaped specimens. The TEM results show that elongated and parallel grains are the major characteristics of the transition region between the matrix and the centre of the ASB. The central region of the ASB consists of ultrafine and equiaxed recrystallized grains with a typical size of 100 nm. According to the classical one-dimensional Fourier heat conduction equation and recrystallization theory calculations, it is proved that ultrafine and equiaxed recrystallized grains did not undergo significant growth during the cooling stage after deformation. The thermodynamics and kinetics calculated results indicate that instant grain refinement within the ASB is due to the rotational dynamic recrystallization (RDR) that occurs during the deformation process.

The effects of wood fiber directions on bonding performance

Using engineered wood products (EWPs) in the building technologies is very crucial in terms of sustainable approaches. They provide; low weight, high structural stiffness, carbon storage capacity and easy erection on site. EWPs are composite materials that are influenced by a variety of factors that play a critical role in their formation. The chemical ingredients of the wood, the curing process of the adhesive, the type of wood, the relationship between the adhesive and the wood species, the curing temperature, the geometric configuration of the lamellae, etc. can all be included under the heading of these factors. In contrary with massive wood, to obtain EWPs different types of adhesives can be used. Therefore adhesive type and its application method affects the quality of wooden structural element. Choosing the appropriate adhesive is one of the steps to be taken to obtain the structurally correct product. Based on this approach, it was decided to investigate the adhesion performance of different adhesive types. This paper aims to present the best bonding method among the melamine urea formaldehyde (MUF) and epoxy adhesives by considering the fiber directions of the wood and the type of adhesive according to the load. One of the aims of this study is to investigate the effect of changing the fiber direction of wood on adhesion performance, taking into account the current gap in the literature. Pull-off tests were conducted to assess the bonding performance of different types of adhesive in wood samples with varying fiber direction. The wood samples were bonded to the wood surface with varying grain directions. During the pull-off tests, ruptures in the glue line of the test samples were commonly observed. The results have shown that in cylindrical samples bonded with epoxy, the highest bonding strength values were observed in scenarios where the wood fibers were oriented parallel to the load direction and perpendicular to the ground plane. Similarly, for wood samples used as the bonding surface, the highest bonding strength values were achieved when the wood fibers were oriented parallel to the load direction and perpendicular to the surface plane. On the other hand, the highest value in pull-off test setups was found with melamine urea formaldehyde adhesive; commonly used in laminated timber, between the wood samples with grains perpendicular to the load direction and the wood adherence surfaces with a parallel grain direction. In summary, the highest strength value was obtained from the test setup in which epoxy was used as the adhesive and both the wood specimens and the wood bonding surface had fiber directions parallel to the load direction.

Experimental investigation on microstructure and properties of Al alloy-PEEK joint with different surface structure obtained by hot-pressing

In this study, selective laser melting (SLM) additive manufacturing was used for the fabrication of Al alloy with the surface structure based on the construction of mechanical interlocking mechanism to complete the joining with polyetheretherketone (PEEK). The application of hot-pressing process provided a direct joining between Al alloy-PEEK at 460 °C for 40 min. This work characterized the forming of both cylindrical and trapezoidal structures, indicating that the structures were formed completely, and the gaps were clear. Although some dimples or micropores were generated in the forming solid, these defects in the forming were beneficial for the flowing and filling of PEEK during hot-pressing joint. The microstructure of Al plate fabricated by SLM showed typical parallel columnar grains perpendicular to the deposition direction and stacked and fish scale like feature in the deposition direction, respectively. The microstructure characterizations of Al alloy-PEEK joints showed that both materials were joined without gaps and formed a strong mechanical interlocking, guaranteeing a firm bond with maximal tensile shear strength up to 81 MPa for trapezoidal structure. By comparison, the joint with cylindrical structure possessed a low 65 MPa shear strength due to weak cuneiform anchor interlocking. Fracture surface was investigated in more detail. The result showed that the joint with cylindrical structure mainly showed interfacial failure and pulling-out, tilting deformation and fracture of the supporting, while the joint with trapezoidal structure exhibited a separation between the top surface of the supporting and the PEEK and brittle cohesive fracture of the PEEK between the gaps.

Magneto-Transport and Enhanced Spin-Polarized Photo Response in Solution-Processed Vertically Aligned Zn0.9Ni0.1O Nanowires

In this study, we grew pristine and Ni-doped vertically aligned zinc oxide nanowires (NWs) on a glass substrate. Both the doped and pristine NWs displayed dominant 002 peaks, confirming their vertical alignment. The Ni-doped NWs exhibited a leftward shift compared to the pristine NWs. TEM measurements confirmed the high crystallinity of individual NWs, with a d-spacing of ~0.267 nm along the c-axis. Ni-doped NWs had a higher density, indicating increased nucleation sites due to nickel doping. Doped NW films on glass showed enhanced absorbance in the visible region, suggesting the creation of sub-gap defect levels from nickel doping. Magnetization vs. magnetic field measurements revealed a small hysteresis loop, indicative of soft ferromagnetic behavior. Current transient plots demonstrated an increase in current with an applied magnetic field. Two-terminal devices exhibited a photo response that intensified with magnetic field application. This increase was attributed to parallel grain alignment, resulting in enhanced carrier concentration and photo response. In the dark, transport properties displayed negative magnetoresistance behavior. This magneto-transport effect and enhanced photo response (under an LED at ~395 nm) were attributed to giant magnetoresistance (GMR) in the aligned NWs. The observed behavior arose from reduced carrier scattering, improved transport properties, and parallel spin alignment in the magnetic field.

Anisotropic grain boundary diffusion in binary alloys: Phase-field approach

In this study, we generalize the phase-field model of grain boundary diffusion in polycrystalline materials. Solute transport is described by the modified Cahn-Hilliard equation accounting for diffusion anisotropy, different interaction parameters in grain boundary region and grain bulk, as well as concentration-dependant mobility. The numerical results are provided for solute transport in plain parallel grains and pollycrystalline medium with various directions of fastest (slowest) solute diffusion. This model predicts subdiffusive power-law dependence for propagation of the concentration profile with the exponent varying in a wide range (α=0.25−0.37 for B-type, α=0.45 for C-type kinetics of grain boundary diffusion). Within the proposed phase-field approach, we confirm the validity of Levine-MacCallum conclusion on concentration profile dynamics and modify the ratios for estimation of the effective values of grain boundary mobility.

Properties of cross-laminated oriented bamboo scrimber board (CL-OBSB)

Physical and mechanical properties were evaluated for cross-laminated oriented bamboo scrimber board (CL-OBSB). Results of non-destructive testing revealed a linear relationship of parallel grain content with ultrasonic-wave velocity, dynamic modulus of elasticity (DMOEu), tap-tone velocity, and DMOEt values. In terms of the ratio of parallel grain, CL-OBSB 80%(//) possessed the highest modulus of elasticity and modulus of rupture values along with the greatest strength. The high grain content compressed in a parallel direction contributed to superior strength performance. Regarding the perpendicular compressive (C┴) strength, because both the CL-OBSB 40%(//) configuration and CL-OBSB have a mid-layer consisting of 60% parallel grain, CL-OBSB 40%(//) holds the largest C┴ value. Furthermore, the shear bond strength (S) showed that the S// value was 1.03 times that of the S┴ value with a wood failure frequency of 97%. After the dimensional stability test, the water absorption and volumetric swelling of the four CL-OBSB types ranged between 15.3% and 17.7% and 9.5% to 10.6%, respectively. In conclusion, the orthogonal configuration of CL-OBSBs can improve balance expansion and contraction in different directions, thus increasing its dimensional stability.

Mechanical properties and failure mechanisms of engineering bamboo scrimber

This study aims to systematically investigate the mechanical properties of bamboo scrimber (BS) along three main loading directions. Through tensile, compression, and shear tests, the mechanical properties of BS were obtained and compared with those of other engineering timber or bamboo products. The results illustrated that the mechanical properties of the BS were affected by the loading direction, and the mechanical properties of the BS along the parallel grain direction were better than those of the BS along the other two perpendicular grain directions. In addition, the results from the comparison between the BS and other engineering timber and bamboo products show that the BS has better mechanical properties. Finally, based on a comparison between various proposed compressive stress–strain relationship molds, this study modified the existing compressive strain–stress relationship model of the BS along the parallel grain direction. The modified multiorder function model has better prediction accuracy, providing a reference for theoretical analysis and related engineering applications of the BS.

A new lycophyte megaspore, Paxillitriletes permicus, from the upper Permian of Southwest China

Lycophytes were an important group of plants in the late Permian (Lopingian) vegetation of Southwest China. However, our understanding of these lycophytes is based mostly on the study of megafossil specimens. Here, we describe a unique lycophyte megaspore, Paxillitriletes permicus Sui, McLoughlin et Feng sp. nov., from the Lopingian Xuanwei Formation of Yunnan Province, Southwest China. This trilete megaspore is characterized by prominent membraneous triradiate flanges, long bifurcate spines, an arcuate ridge expanded into a zona, and triangular to polygonal reticulate sculpture. Ultrastructural analysis reveals that the megaspore wall consists of four layers. The innermost layer is the foot layer, which forms a thin and solid basal lamina. It is covered by a dense layer containing small and parallel sporopollenin grains. A thick spongy layer is developed exterior to the dense layer and consists of elongate, curved, and intersected sporopollenin units with porous zones. The outermost layer is dense, of variable thickness, and forms the processes. Morphological and ultrastructural features indicate that the new megaspore belongs to a herbaceous isoetalean. This is the first detailed investigation of megaspores from the Lopingian of China using scanning and transmission electron microscopy. Our discovery represents the oldest occurrence of Paxillitriletes, and adds to the diversity of late Permian lycophytes in the Cathaysian Flora in the paleotropics of the eastern Tethys Ocean.

Experimental Bond Behaviour of Glued-In Rod Connection for Mengkulang Glulam under Pull-Out Loading

Mechanical joint and adhesive joint are the two most common types of timber connections. In the case of timber construction, bonded-in rods offer a long-term, aesthetically acceptable alternative to some of the more conventional steel moment connections. Bonded-in rod connections in timber need many desirable attributes inefficiency, manufacture, performance, aesthetics and cost. This paper presents pull-out experimental testing for glued-in rod made of Mengkulang (tarrietia javanica) glulam joints. Hundred and seven (107) specimens were prepared, each with a single glued-in rod parallel and perpendicular to the grain. The steel treaded rod with a diameter of 12 mm, 16 mm and 20 mm with three numbers of adhesive (Sikadur-30) thicknesses of 2 mm, 3 mm and 4 mm were used in this experiment. The pull-out tests observations were on the effects of adhesive thickness, parallel and perpendicular grain directions and modes of failure of the specimens. The result obtained that 4 mm adhesive thickness was the strongest and parallel specimens showed better results than the perpendicular specimens. The pull-out failure modes are affected by the selected factors, i.e. the adhesive thickness, rod diameter and grain directions. Most of the specimens show failures in the timber besides the adhesive to timber interface.

Growth of YBa2Cu3O7 Films with a Packet of Parallel Grain Boundaries Spaced by Nanometer Distances

Growth of YBa2Cu3O7 Films with a Packet of Parallel Grain Boundaries Spaced by Nanometer Distances

Atomistic simulation of bicrystal behaviour with Σ5 grain boundary parallel to nanometric cutting direction

Molecular dynamics simulations were performed to study the behaviour of bicrystals in the nanometric cutting process with symmetric Σ5(210) grain boundary. Several copper bicrystals with various grains sizes were simulated using embedded atoms potential. Results showed that when a grain boundary was located at a high hydrostatic pressure area, at upstream of the cutting tool, it was diffused to lower grain by hydrostatic pressure. On the other hand, the grain boundary located at downstream of the tool was migrated to the machined surface with the evaluation of crystallographic orientation in adjacent atoms structure. Although in bicrystals with parallel grain boundary, defects initiate from tool edge similar to single crystals, defects propagation was significantly increased in bicrystal substrate caused the increment of plastic deformation and potential energy. Finally, these defects merged to grain boundary without transmission or reflection into the adjacent grain, increasing stress concentration and residual stress.

Effects of beam oscillation modes on microstructure and mechanical properties of laser welded 2060 Al-Li alloy joints

In the present work, laser welding of 2-mm-thick 2060 Al-Li alloy was performed under different beam oscillation modes. Weld seam morphology, microstructure, mechanical properties were compared. The results indicated that joints welded by oscillated laser beam possessed improved collapse, refined grains, higher microhardness and tensile strength. In fusion zone, nondendritic equiaxed grains, parallel dendrite grains and cellular dendrite grains were formed in all welded joints. After applying laser beam oscillation, the collapse decreased from 0.54 mm to 0.1 mm. The maximum tensile strength of welded joint was obtained in the case of ‘8′ shaped laser beam oscillation reaching 338.15 MPa, which was improved by 68% compared with that of joint without oscillation (200.58 MPa). In this case, grain characters and molten pool fluid were studied to reveal the enhancement mechanism of beam oscillation. Enhanced fluid velocity produced with ‘8′ shaped laser oscillation refined grains and more high angle grain boundaries (HAGBs) were formed. The grain size was reduced from 105.27 μm to 89.67 μm in cellular dendrite zone (CDZ). The percentage of HAGBs increased from 65.2% to 75.2%. The refined grains resulted in larger and more uniform microhardness value and better mechanical behavior. Shallower, crystal-sugar shaped dimples were formed in fracture surface obtained by pure laser welding without oscillation while deeper and bigger dimple, including equiaxed dimple and conical dimple were generated in the fracture surfaces of oscillated laser welded joints.

Atomic Layer Deposition of Textured Li4 Ti5 O12 : A High-Power and Long-Cycle Life Anode for Lithium-Ion Thin-Film Batteries.

The "zero-strain" Li4 Ti5 O12 is an attractive anode material for 3D solid-state thin-film batteries (TFB) to power upcoming autonomous sensor systems. Herein, Li4 Ti5 O12 thin films fabricated by atomic layer deposition (ALD) are electrochemically evaluated for the first time. The developed ALD process with a growth per cycle of 0.6Åcycle-1 at 300°C enables high-quality and dense spinel films with superior adhesion after annealing. The short lithium-ion diffusion pathways of the nanostructured 30 nm films result in excellent electrochemical properties. Planar films reveal 98% of the theoretical capacity with 588 mAh cm-3 at 1 C. Substrate-dependent film texture is identified as a key tuning parameter for exceptional C-rate performance. The highly parallel grains of a strong out-of-plane (111)-texture allow capacities of 278 mAh cm-3 at extreme rates of 200 C. Outstanding cycle performance is demonstrated, resulting in 97.9% capacity retention of the initial 366 mAh cm-3 after 1000cycles at 100 C. Compared to other deposition techniques, the superior performance of ALD Li4 Ti5 O12 is a breakthrough towards scalable high-power 3D TFBs.