Favorable Grain Research Articles

Grain Size Measurements of the Eolian Stimson Formation, Gale Crater, Mars and Implications for Sand Provenance and Paleoatmospheric Conditions

AbstractThe Stimson formation is a late‐infilling eolian sandstone in Gale crater, Mars that formed from sand accumulation in a dune field analogous to the modern active Bagnold dune field, enabling a unique opportunity to compare the past to the present dune fields on Mars. Previous work suggested that the Stimson has a coarser grain‐size distribution than the active Bagnold dunes based on three images of the Stimson. We analyze grain size in the Naukluft and Emerson plateaus of the Stimson by observing 115 images throughout the formation to classify textures and quantitatively measuring grains in eight representative individual images. Results indicate that the Stimson has a primary grain size mode at <200 μm. In addition, more than 50% of the observed Stimson rock targets display a coarser grain population with a long‐tailed distribution including grains ∼600–1200 μm. The primary grain size mode is similar to that observed in the Bagnold dunes, but the coarse grain size mode was neither observed in the Bagnold dunes nor in ripples adjacent to the dune field. Models for saltation mechanics indicate that the favored grain size for eolian transport on Mars, ∼100–200 μm, is independent of atmospheric density, though atmospheric density affects the wind speeds at which grains can be transported by winds. We conclude that the source of the Stimson dunes was more proximal and coarser than the source of the Bagnold dunes and that the paleoatmosphere was likely not significantly denser than the modern Martian atmosphere.

Genetic loci associated with sorghum drought tolerance in multiple environments and their sensitivity to environmental covariables.

Climate change can limit yields of naturally resilient crops, like sorghum, challenging global food security. Agriculture under an erratic climate requires tapping into a reservoir of flexible adaptive loci that can lead to lasting yield stability under multiple abiotic stress conditions. Domesticated in the hot and dry regions of Africa, sorghum is considered a harsh crop, which is adapted to important stress factors closely related to climate change. To investigate the genetic basis of drought stress adaptation in sorghum, we used a multi-environment multi-locus genome-wide association study (MEML-GWAS) in a subset of a diverse sorghum association panel (SAP) phenotyped for performance both under well-watered and water stress conditions. We selected environments in Brazil that foreshadow agriculture where both drought and temperature stresses coincide as in many tropical agricultural frontiers. Drought reduced average grain yield (Gy) by up to 50% and also affected flowering time (Ft) and plant height (Ph). We found 15 markers associated with Gy on all sorghum chromosomes except for chromosomes 7 and 9, in addition to loci associated with phenology traits. Loci associated with Gy strongly interacted with the environment in a complex way, while loci associated with phenology traits were less affected by G × E. Studying environmental covariables potentially underpinning G × E, increases in relative humidity and evapotranspiration favored and disfavored grain yield, respectively. High temperatures influenced G × E and reduced sorghum yields, with a ~ 100kgha-1 average decrease in grain yield for each unit increase in maximum temperature between 29 and 38°C. Extreme G × E for sorghum stress resilience poses an additional challenge to breed crops for moving, erratic weather conditions.

Differences in the Appearance Quality of Soft Japonica Rice with Different Grain Shapes in the Yangtze River Delta and Their Relationship with Grain-Filling

This study investigated the differences in appearance quality among different soft japonica rice varieties based on grain shape, with a particular focus on the broad-ovate soft japonica rice varieties Nanjing 9108 and Nanjing 5718, as well as the slender soft japonica rice varieties Shangshida 19 and Jiahe 218, all sourced from the Yangtze River Delta. The results showed that the slender soft japonica rice varieties exhibited significantly superior appearance quality compared to the broad-ovate varieties. In the case of superior grains, the chalky grain rate of the broad-ovate soft japonica rice was 4307.79 percent higher than that of the slender varieties, and the degree of chalkiness was 8275.00 percent higher. For inferior grains, the chalky grain rate of the broad-ovate soft japonica rice was 238.34 percent higher than the slender varieties, and the degree of chalkiness was 339.96 percent higher. In contrast to the slender soft japonica rice, the broad-ovate varieties had a lower percentage of high-weight grains and a higher percentage of low-weight grains. Compared to the broad-ovate soft japonica rice, the slender varieties exhibited a faster grain-filling rate and shorter effective grain-filling days. Correlation analysis revealed that chalkiness had a significant negative correlation with grain length and aspect ratio. Simultaneously, chalkiness also showed a positive correlation with the number of effective grain-filling days while demonstrating a negative correlation with both the maximum and average grain-filling rates. The slender soft japonica rice exhibited a lower likelihood of developing chalkiness and higher grain-filling efficiency and developed a favorable grain weight distribution. These distinctive attributes significantly contribute to the superior appearance quality of the slender japonica soft rice.

Second phase strengthening and grain boundary segregation effects on the microstructure and properties of (Ce, Y)-TZP-based ceramics prepared by vat photopolymerization

Immediate implant placement (IIP) has garnered significant attention due to its minimally invasive approach and ability to facilitate immediate crown replacement. Nevertheless, challenges persist in processing complex geometries and selecting suitable materials. This study successfully fabricated high-performance, complex-structured (Ce, Y)-TZP-based composite ceramics using vat photopolymerization (VPP) technology, combining second-phase strengthening and grain boundary segregation effects. The incorporation of α-Al2O3 as a secondary phase led to a progressive refinement of (Ce, Y)-TZP grains, with the most favorable grain size achieved at 20 wt% α-Al2O3, reducing the average grain size to 0.75 μm. However, excessive α-Al2O3 content resulted in micropore formation, compromising the material's mechanical performance. At an optimal concentration of 15 wt% α-Al2O3, the composite exhibited superior mechanical properties, including a Vickers hardness of 11.53 ± 0.27 GPa and a flexural strength of 525.5 ± 21.3 MPa. Despite these improvements, some coarse (Ce, Y)-TZP grains persisted within the ceramic matrix. To further enhance grain refinement at lower α-Al2O3 content, a minimal addition of La3+ (0.1 wt%) was introduced, promoting grain boundary segregation and additional grain refinement. This modification reduced the (Ce, Y)-TZP grain size to 0.74 μm, increased hardness to 13.03 ± 0.31 GPa, and elevated flexural strength to 550.4 ± 39.8 MPa, while maintaining excellent material stability.

Viability of WAAM for fabrication/repair of SS316: Fatigue crack growth behavior for varied notch locations in the vicinity of WAAM-substrate interface

The tensile and fatigue crack growth rate (FCGR) behavior of SS316L wire deposited on SS316 substrate using wire arc additive manufacturing (WAAM) was studied to assess its potential for fabrication and repair applications. Five initial notch locations near the WAAM-substrate interface were considered for FCGR. Cracks in the deposition direction propagated towards the WAAM region. FCGR of cracks in the build direction accelerated in the WAAM region due to its favorable columnar grain orientation. Overall, FCGR behavior near the WAAM-substrate interface is comparable with wrought alloy, suggesting WAAM’s viability for SS316 fabrication and repair, with satisfactory structural integrity observed in tensile and FCGR behavior.

Multi-trait index: selection and recommendation of superior black bean genotypes as new improved varieties

Common bean provides diet rich in vitamins, fiber, minerals, and protein, which could contribute into food security of needy populations in many countries. Developing genotypes that associate favorable agronomic and grain quality traits in the common bean crop could increase the chances of adopting new cultivars black bean. In this context, the present study aimed at selection of superior black bean lines using multi-variate indexes, Smith-Hazel-index, and genotype by yield*trait biplot analysis. These trials were conducted in Campos dos Goytacazes - RJ, in 2020 and 2021. The experimental design used was randomized blocks, with 28 treatments and three replications. The experimental unit consisted of four rows 4.0 m long, spaced at 0.50 m apart, with a sowing density of 15 seeds per meter. The two central rows were used for the evaluations. The selection of superior genotypes was conducted using the multiple trait stability index (MTSI), multi-trait genotype-ideotype distance index (MGIDI), multi-trait index based on factor analysis and genotype-ideotype distance (FAI-BLUP), Smith-Hazel index, and Genotype by Yield*Trait Biplot (GYT). The multivariate indexes efficiently selected the best black bean genotypes, presenting desirable selection gains for most traits. The use of multivariate indexes and GYT enable the selection of early genotypes with higher grain yields. These lines G9, G13, G17, G23, and G27 were selected based on their performance for multiple traits closest to the ideotype and could be recommended as new varieties.

Multi-scale microstructure manipulation of an additively manufactured CoCrNi medium entropy alloy for superior mechanical properties and tunable mechanical anisotropy

Laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) technology has become a versatile tool for producing new microstructures in metal components, offering novel mechanical properties for different applications. In this work, enhanced ductility (∼55% elongation) and tunable mechanical anisotropy (ratio of ductility along vertical to horizontal orientation from ∼0.2 to ∼1) were achieved for a CoCrNi medium entropy alloy (MEA) by multi-scale synergistic microstructure manipulation (i.e., melt pool boundary, grain morphology and crystallographic texture) through adjusting key PBF-LB processing parameters (e.g., laser power and scan speed). By increasing the volumetric energy density (VED) from 68.3 to 144 J/mm3, the melt pool size enlarges, and the crystallographic texture transitions from <100>//BD to <110>//BD due to the maximum thermal flux direction changing for different melt pool dimensions, which affects the proportion of grains that have different growth directions. Moreover, excellent mechanical properties of 890 MPa ultimate tensile strength and ∼55% elongation to failure can be achieved for loading perpendicular to the build direction with only a ∼15% reduction in properties for loading along the build direction. The superior combination of mechanical properties is achieved by processing parameter-controlled strengthening of melt pool boundary interfaces, heterogeneous deformation induced strengthening through bimodal grain structures, and favorable grain orientation for dislocation slip and twinning formation, which was significantly more activated in the <110>//BD texture than in the <100>//BD. This study offers new insights into achieving multi-scale synergistic microstructure manipulation via PBF-LB for desired strength, ductility, and mechanical anisotropy in a CoCrNi MEA.

Numerical simulation of microstructure evolution in molten pool of nickel-based superalloy during selective laser melting

The competitive growth and the evolution of grain/dendrite structures of IN718 superalloy in the molten pool during selective laser melting (SLM) were investigated with the finite element method (FEM) coupling the phase-field model (PFM). The thermal evolution was solved by the FEM and then the results were input into the PFM model to simulate the microstructure evolution involving grain nucleation, grain epitaxial growth and grain competition. Based on the analysis of microstructure evolution of the transverse and longitudinal sections of the molten pool, the mechanism of dendrite competitive growth in the SLM process was discussed and the concentration distribution of the solute element Nb in the molten pool was quantitatively calculated. The results show that the dendrite competitive growth is affected by both the temperature gradient and the crystallographic orientation. The unfavorable orientation grain with a high misorientation (>22.5°) will be eliminated by the favorable orientation grain quickly.

Analysis of the geotechnical and mineralogical characteristics of the Settat-Khouribga shale clay for potential civil engineering applications

This study provides a comprehensive analysis of clay shale from the Settat-Khouribga region, assessing its suitability for civil engineering applications through various tests. Grain size distribution, hardness (MDE, LA), and plasticity (ES 0/5, IP, VB) tests, along with consistency index evaluations following the "CSTCN" catalog, were conducted. X-ray diffraction (XRD) and mineralogical analyses identified key components such as quartz, calcite, feldspar, and iron oxide, with quartz being predominant. The results demonstrated that the shale clay is well-suited for construction purposes, exhibiting favorable grain size distribution and high resistance to wear and abrasion, which are crucial for material durability. Its low plasticity further indicates good mechanical stability in construction projects. SEM analysis revealed a microstructure dominated by quartz grains, montmorillonite, and illite lamellae, and the presence of micro fissures and pores suggests both strengths and potential durability concerns. Advanced statistical analyses, including Principal Component Analysis (PCA) and regression models, were employed to assess geotechnical properties. The study confirms the shale's compliance with construction standards, highlighting its potential for sustainable building practices. These findings contribute significantly to the field of geotechnical engineering, emphasizing the material's suitability for construction and its broader societal implications.

Contextual relationship between mechanical heterogeneity and dyking: constraints from magma emplacement dynamics of the ca. 2.21 Ga Anantapur–Kunigal mafic dyke swarm, Dharwar Craton, India

AbstractMafic dykes are typically emplaced through primary hydraulic fracturing of undeformed crust or may make use of pre-existing crustal inhomogeneities, representing the plumbing systems of a large igneous province. The Eastern Dharwar Craton has dense exposures of several generations of Paleoproterozoic mafic dyke swarms ranging from ca. 2.37 Ga to ca. 1.79 Ga. Herein, using anisotropy of magnetic susceptibility fabric data of mafic dykes and associated host granites, the emplacement systematics of the NW- to W-trending ca. 2.21 Ga Anantapur–Kunigal dyke swarm, displaying a radiating geometry, have been studied to understand magma flow dynamics. A low-angle relationship between the silicate and opaque fabrics and good correlation with magnetic lineation, identified via petrographic studies and shape preferred orientation analyses of multiple oriented thin sections, suggest a primary flow-related magnetic anisotropy for the studied dyke samples. The classic subparallel relationship between the trend of the dyke planes and magnetic fabric of the associated host granites suggests that the radiating geometry of the ca. 2.21 Ga dyke swarm was supported by a favourable pre-existing structural grain of the country rock. We interpret the magma for the studied dyke swarm was fed laterally from a distant plume. It was emplaced as laterally propagating primary dyke fractures as well as injected into the pre-existing subparallel crustal inhomogeneities. Corroborating all these inferences, a detailed emplacement model for ca. 2.21 Ga Anantapur–Kunigal dyke swarm is also proposed.

Extent and significance of the Racklan–Forward Orogen in Canada: far-field interior reactivation during Nuna assembly

Abstract Mesoproterozoic orogenesis is well established on the western and southern flanks of Laurentia in the well-known Racklan–Forward and Mazatzal orogens, but its significance within the previously assembled interior of the supercontinent Nuna has not been established. We examine regional isotopic and structural evidence for Mesoproterozoic deformation in the c. 1.7–1.63 Ga Hornby Bay, Elu, Thelon and Athabasca intracontinental basins, and present evidence for Mesoproterozoic reactivation of Paleoproterozoic structures in the Wopmay and Trans-Hudson orogens. The Racklan–Forward Orogeny in the interior of north Laurentia comprises north–south-trending, high-angle, east-vergent folds and thrusts that occur across a region 1660 km wide and over 1000 km long, stretching from the Yukon to near Hudson Bay and from Banks Island to below the Western Canada Sedimentary Basin. The structures progress from ductile amphibolite and greenschist facies in the Racklan type area to sub-greenschist facies and ultimately brittle or brittle-ductile in the far foreland, showing a predominant thick-skinned style typical of many intracontinental orogens. We present compiled low-temperature thermochronological data, including ages of spatially associated uraninite mineralization, to characterize the scope of reactivation of basement structures in the Archean Rae craton in Nuna's interior. We compare the nature of widespread far-field reactivation in the Racklan–Forward Orogen with other orogens of Nuna's assembly to show it is unusual for Nuna's peripheral margin. We suggest that c. 1.6 Ga continent–continent collision of North Australia with NW Laurentia propagated stresses far into the interior as a result of combined favourable pre-existing structural grain and a weak subcontinental lithospheric mantle in the Rae craton due to repeated episodes of refertilization across 500 Ma of accretion and intrusion. Cratons that experience the complex, two-sided collision and protracted upper plate setting during supercontinent assembly noted herein may be particularly susceptible to extensive foreland propagation of peripheral orogens.

Construction of grain boundary for accelerated ionic diffusion in Ta5+-substituted Na3V2(PO4)3 with high performance for full sodium ion batteries

Na3V2(PO4)3 (NVP) stands out among many cathode materials due to its three-dimensional structure. Nevertheless, its poor inherent conductivity seriously hinders its development. Herein, NVP system is modified by Ta5+ doping for the first time. The introduction of Ta5+ at V3+ site can bring beneficial n-type doping. Due to the high valence of Ta5+, donor levels are generated and more electrons are activated, which can efficiently improve the electronic conduction. Furthermore, the migration pathway of Na+ can be expanded after Ta5+ doping with larger ionic radius. Meanwhile, Ta5+ act as pillar ions to support the crystal framework to enhance the stability of NVP. Significantly, the Ta5+ can be partially reduced to Ta3+ by carbon during the carbothermal reduction reaction and than combines with N to form the TaN product in the N2-filled atmosphere. This new conductive TaN phases with excellent electronic conductivity stuck in the NVP crystal structure to generate favorable grain boundary. Benefiting from the heterojunction, the diffusion of Na+ can be greatly accelerated in the grain boundary rather than in the NVP bulk. Comprehensively, the kinetic characteristics of NVP can be significantly improved by Ta5+ doping. Accordingly, the modified NVP-Ta0.05/C reveals a high capacity of 129.6 mA h g−1 at 0.1C and releases a reversible value of 115.5 mA h g−1 at 1C with remained capacity of 100.9 mA h g−1 after 100 cycles. It still delivers a capacity of 95.79 mA h g−1 at 12C with a high retention of 79.83% after 100 cycles. Moreover, the assembled NVP-Ta0.05/C//CHC full cell delivers a capacity of 100 mA h g−1 at 0.1C, indicating its superior application potential.

Grain boundary engineering activated by residual stress during the laser powder bed fusion of Inconel 718 and the electrochemical corrosion performance

Conventional grain-boundary engineering (GBE) is not directly compatible with the complicated geometric parts fabricated via laser powder bed fusion (LPBF) owing to the multiple thermomechanical processes involved therein. In this study, GBE was activated by the inherent residual stress of an Inconel 718 superalloy produced via LPBF. The grain boundary character distribution and corresponding electrochemical corrosion behaviors were systematically investigated in a 3.5 wt% NaCl solution. The results indicate that numerous Σ3 boundaries (twin boundary, 64.89%) can be obtained via a simple heat treatment, and a favorable grain size can be maintained owing to the segmentation effect of the twin boundary. The corrosion resistance is closely related to the fraction of low special low-coincidence site lattices because the random boundary networks are broken. In addition, samples fabricated using GBE with the highest fraction of the twin boundary exhibited more compact and stronger passive films. The main components (oxide and metallic states) of thicker passive films provided intrinsic protection for the matrix. This study demonstrates a feasible method for GBE in additive-manufactured superalloys for fabricating complicated geometric parts with unique properties.

Roles of the grain-boundary characteristics and distributions on hydrogen embrittlement in face-centered cubic medium-entropy VxCr1-xCoNi alloys

The issue of hydrogen embrittlement (HE) in face-centered (FCC) structured alloys is significant for H storage and transportation application due to unanticipated damage beyond its predicted service life. This unpredictable situation may harm human life and limit hydrogen to a reliable source of renewable energy in industrial fields. Recent research has suggested that multi-principal element alloys possess high resistance to HE. However, there has been limited exploration of how their unique properties affect the HE mechanisms. In this study, using simple model VCrCoNi alloys with analogous grain sizes, the reduction rate of ductility by hydrogen uptake was measured through a slow strain rate tensile test following electro-chemical H charging. Further, the origin of HE resistance was investigated by analyzing various factors such as hydrogen contents, fracture and deformation behaviors, and grain boundary properties using thermal desorption spectroscopy, scanning electron microscope, and electron backscatter diffraction. Despite the consistent trends of the H content, stacking fault energy, and stress with increasing V content, the resistance to HE is the highest for the alloy with an intermediate ratio of V and Cr, namely, for the V0.7Cr0.3CoNi alloy. Through the analysis of grain boundary characteristics, the high resistance is attributed to large fractions of special boundaries and special triple junctions and large twin-related domain size, which suppresses crack growth and interlinkage. The favorable grain boundary characteristics result from mechanical dynamic recovery, achieved by the competitive effects of solid-solution strengthening and stacking fault energy. Thus, the present study provides novel insights into enhancing HE resistance in FCC-structured alloys.

Ferroelectric domain percolation in polycrystals

Ferroelectric materials possess the ability to switch between polarization states on application of external fields. This switching is facilitated via movement of domains walls and is a critical factor in the performance metrics of these materials. Hence, the interaction of domain walls with microstructural features such as grain boundaries can influence their performance. Experimentally, domain continuity has only been observed over a few grains with no information of the domain percolation length in larger polycrystals. For domain continuity to be energetically feasible, conditions of ferroelectric polarization continuity and domain wall plane matching need to be satisfied at the grain boundary. In this work, we have studied the extent of continuity of domains within modelled polycrystals. It is shown that under tighter conditions of plane matching and uncompensated polarization charge, favorable grain boundary character can have considerable impact on the domain percolation. However, when the conditions of domain continuity are relaxed, due to higher charge and geometric tolerance, domain percolation throughout the polycrystal is a likely phenomenon. It is shown that percolation of domains through a polycrystalline ferroelectric could be tailored by microstructural control of the grain boundary types and defect chemistry control of the charge compensation mechanisms. The ability to manipulate the length-scale of correlated domain wall motion may lead to new opportunities in ferroelectric functional device design. Additionally, these results can be extended to study the effect of grain boundary character on other material phenomena that involve planar interactions at grain boundaries, including ferroelastic twin boundaries and slip plane continuity.

Evaluation of Thermal Fatigue Life and Crack Morphology in Brake Discs of Low-Alloy Steel for High-Speed Trains.

Effective braking in high-speed trains is one of the major bottlenecks in expediting the technology and possibilities to improve speed. Although substantial progress has been made to increase operating speed, perhaps, thermal fatigue cracking in brake discs is a primary constraint so far. Thermal fatigue cracking is the major cause of brake disc failure in high-speed trains, especially trains with a speed of 350 km/h or above. In this study, new material composition is proposed for brake discs of high-speed trains. A comprehensive investigation is presented based on fatigue crack initiation and propagation, along with wear and micro-hardness characterization. Thermal fatigue tests at various thermal cycles between 20 ℃ and 700 ℃ were performed and the experimental results are compared with fatigue properties of a commercial brake disc material. An experimental trial revealed that thermal cracks normally initiate and propagate along the oxidized grain boundaries; nevertheless, crack propagation is restricted by the fine precipitates and lath structure of martensitic. Moreover, crack length at the initiation and propagation stage is predicted through crack growth rate and favorable grain size in the crack vicinity. Thermal fatigue life can be improved by dictating the microstructure and precipitate morphology of cast steel by tailoring the alloying composition.

On the Impact of Additive Manufacturing Processes on the Microstructure and Magnetic Properties of Co–Ni–Ga Shape Memory Heusler Alloys

Microstructure design allows to prevent intergranular cracking and premature failure in Co–Ni–Ga shape memory alloys. Favorable grain boundary configurations are established using additive manufacturing techniques, namely, direct energy deposition (DED) and laser powder bed fusion (L‐PBF). L‐PBF allows to establish a columnar grain structure. In the Co–Ni–Ga alloy processed by DED, a microstructure with strong ⟨001⟩ texture is obtained. In line with optimized microstructures, the general transformation behavior is essential for performance. Transition parameters such as transition temperature and thermal hysteresis depend on chemical composition, homogeneity, and presence of precipitates. However, these parameters are highly dependent on the processing method used. Herein, the first‐order magnetostructural transformation and magnetization properties of Co–Ni–Ga processed by DED and L‐PBF are compared with single‐crystalline and as‐cast material. In the alloy processed by L‐PBF, Ga evaporation and extensive formation of the ferromagnetic Co‐rich γ'‐phase are observed, promoting a very wide transformation range and large thermal hysteresis. In comparison, following DED, the material is characterized by minor chemical inhomogeneity and transition and magnetization behavior being similar to that of a single crystal. This clearly renders DED‐processed Co–Ni–Ga to become a promising candidate material for future shape memory applications.

Effects of Bi doping on structural and magnetic properties of cobalt ferrite perovskite oxide LaCo0.5Fe0.5O3

Literature reports on magnetic transition of LaFe0.5Co0.5O3 are highly ambiguous. The present study is an endeavour to address that particular issue of this ferrite perovskite. Here we report the low temperature sol-gel synthesis of pure and Bi-doped La1-xBixFe0.5Co0.5O3 (x = 0, 0.1 & 0.2) perovskites. All the samples were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray (EDX) analysis and magnetization studies. LaFe0.5Co0.5O3 crystallizes in a single phase rhombohedral (R-3c) structure. Substitution of Bi at the A-site results in structural transition. La0.9Bi0.1Fe0.5Co0.5O3 exhibits mixed rhombohedra (R-3c) and orthorhombic (Pbnm) phases, whereas La0.8Bi0.2Fe0.5Co0.5O3 is single phase orthorhombic (Pbnm). Favourable grain growth and good crystallinity observed in Bi doped samples are possibly due to the low melting temperature of Bi containing La1-xBixFe0.5Co0.5O3. EDX analysis confirms the chemical homogeneity of the samples. XPS studies and bond valence sum calculations confirm the nominal cationic oxidation states of the ions. Magnetization measurements reveal the weak ferromagnetic nature of La1-xBixFe0.5Co0.5O3 (x = 0, 0.1 & 0.2) which is associated to the canted antiferromagnetic structure. The magnetically active subsystem of Fe3+ ions are responsible for weak ferromagnetism which is explained by the antisymmetric Dzyaloshinskii–Moriya interaction, whereas the Co3+ ions remain predominantly in the low spin state. The increase in magnetic transition and the lower magnetic moment with an increase in Bi content can be related to the weakening of Dzyaloshinskii–Moriya interaction due to structural modification and local lattice distortion associated to the stereochemically active 6s2 lone pair electrons of the Bi3+ ions. Our results confirm the high structure sensitivity of magnetic properties of cobalt ferrite perovskite.

Five dimensional grain boundary distribution for yttria stabilized zirconia based on experimentally determined macroscopic boundary parameters

Distributions showing the frequencies of occurrence of grain boundaries as functions of their 5 macroscopic boundary parameters have been computed for a set of yttria-stabilized zirconia samples sintered at different conditions and thus having different grain sizes. For this purpose, datasets containing both grain misorientation and boundary plane parameters have been collected by the means of the 3D EBSD technique. Then, the 5-parameter distributions have been computed using the approach based on kernel density estimation. A few top peaks are visible in all of the obtained distributions. Their heights exceed the level of the random distribution by at least about 3 multiples of the corresponding statistical errors. The list of favored grain boundaries includes the Σ3/(111) and Σ11/(11¯3) boundaries, as well as the boundaries having both the boundary plane (100) and misorientation by 10∘ to 37∘ about the [100] axis.The largest of the collected dataset containing 64,506 distinct grain boundaries, and being probably the largest dataset of this kind ever collected for zirconia, allowed to study e.g. rare boundaries like those with high Σ misorientations about the [110] axis.

Favorable grain growth of thermally stable formamidinium-methylammonium perovskite solar cells by hydrazine chloride

Formamidinium methylammonium lead iodine (FAMAPbI3) based perovskite solar cells have reached phenomenal efficiencies recently. However, it is difficult to form pure black α-phase perovskite by solution method. Meanwhile, the formed polycrystalline FAMAPbI3 film often has large amount of grain boundaries, which can consist dangling bonds and iodide ions. Under illumination and heat, iodide ions can easily migrate and oxidize to form iodine, thus decompose the structure of perovskite and reduce the device performance. Herein, hydrazine chloride (HACl) as an additive is employed to promote favorable grain orientation during the growth of perovskite crystals. From grazing incidence wide-angle X-ray scattering (GIWAXS) and scanning electron microscope (SEM), HACl can facilitate strong diffraction signals along crystallographic planes (100) and (200) indicating a strengthened lattice structure for α-phase FAPbI3 and significantly decrease the grain boundaries for reduced carrier recombination. Consequently, the perovskite solar cells (PSCs) with optimized content of HACl lead to a champion power conversion efficiency (PCE) of 22.32% (certified PCEs of 21.59%) in a mesoporous device based on (FAPbI3)0.95(MAPbBr3)0.05 perovskite solar cells. Furthermore, from UV–vis and XPS spectrum, HACl can reduce iodine (I0) to iodide (I-) effectively, meaning the process of decomposition of FAMAPbI3-based perovskite has been greatly inhibited. As a result, unencapsulated device can retain 95% of its original power conversion efficiency after 1400 h of continuous one-sun illumination. Meanwhile, thermal (60 °C) stability is also greatly improved by maintaining 90% of initial efficiency after aging for 1400 h.