Preferred Crystal Orientation Research Articles

Development of Amphibole Crystal Preferred Orientations (CPOs) and Their Effects on Seismic Anisotropy in Deformed Amphibolites

AbstractCrystal preferred orientations and seismic anisotropy of amphibole play a crucial role in fingerprinting the rheological and physical properties of the deep crust. This study presents typical naturally deformed (banded, mylonitic, and ultramylonitic) amphibolites from the Ailao Shan‐Red River shear zone (ASRR‐SZ), southwestern China. In the banded amphibolite, coarse amphibole grains are highly elongated by dislocation creep and develop type I fabric of amphibole. In the mylonitic amphibolite, amphibole grains are characterized by porphyroclasts with core‐mantle structure and fine‐grained amphiboles in the matrix. Subgrain rotation recrystallization dominantly contribute to the grain size reduction process and display type III fabric of amphibole. In the ultramylonitic amphibolite, the fine‐grained amphiboles are mainly deformed by mechanical rotation of prismatic grains and develop type IV amphibole fabric. The seismic anisotropies are calculated from crystal preferred orientation (CPO) of naturally deformed amphiboles and model fabric. They both display that the transition of amphibole fabric from type III through type I to type IV also comes along with the transition of AVp patterns from Vp(X) ∼ Vp(Y) > Vp(Z) through Vp(X) > Vp(Y) > Vp(Z) to Vp(X) > Vp(Y) ∼ Vp(Z). Under the same texture strength, the strongest seismic anisotropy (both AVp and Max. AVs) occurs in the type III fabric of amphibole, the weakest seismic anisotropy is related to type IV fabric and a medium seismic anisotropy in type I fabric. This work indicates that the CPO types of amphiboles need be carefully considered in interpreting observed seismic anisotropy at the deep crustal level.

Distinct Reaction Route toward High Photovoltaic Performance: Perovskite Salts versus Crystals

The synthetical strategy of methylamine (MA) molecular treatment for fabricating perovskite film has been attracting increasing attention because of the ease of fabrication feature and the high-throughput process. In this approach, we found both of perovskite salts (MAI and PbI2) and crystals have been used as the source materials for the interaction with MA molecules. Even though both alternatives are applicable, the reaction routes toward perovskite crystalline film are distinct, which correlates with the photovoltaic performance and the fabrication process design. Therefore, we systematically studied the difference between perovskite salts and crystals with respect to precursor solubility, crystallization dynamics, perovskite crystal structure, and photoelectric properties. The results show the configuration and the crystallization dynamic of the salts and crystal-derived solution are different. The salt-derived solution consists of iodoplumbate complexes, while the crystal-derived solution is composed of perovskite sheet intermediates. Because of the ordered stacking behavior of the perovskite sheet intermediates, the crystal-derived perovskite films showed faster crystallization and preferred crystal orientation, which results in superior charge carrier transport properties and higher conversion efficiency. The disclosure of the distinct features between salts and crystals provides guidelines to modulate the solution chemistry for higher photovoltaic performance.

Self-Assembling Systems for Optical Out-of-Plane Coupling Devices.

Micromirrors are used in integrated photonics to couple extraplanar light into the planar structure of a device by redirecting light via specular reflection. Compared with grating or prism-based couplers, micromirrors allow for coupling of light over a broader range of wavelengths, provided that the micromirror is fabricated with a specific 3D shape to ensure proper reflection angles. In principle, self-assembly methods could enable reliable, parallelizable fabrication of such devices with a high degree of precision by designing self-assembling components that produce the desired microscale geometry as their thermodynamic products. In this work, we use DNA-functionalized nanoparticles to assemble faceted crystallites with predetermined crystal shapes, and demonstrate with microscale retroreflectance measurements that these self-assembled nanoparticle arrays do indeed behave like optically flat mirrors. Furthermore, we show that the tilt angle of the micromirrors can be intentionally controlled by altering the crystallographic symmetry and preferred crystal orientations as a function of the self-assembly process, thereby altering the resulting specular angle in a programmable manner. Measurements of optical coupling from normal incidence into the substrate plane via an optical fiber confirm that the faceted structures can function as optical out-of-plane coupling devices, and coating these structures with reflective materials allows for high efficiency of light reflection in addition to the angular control. Together, these experiments demonstrate how self-assembled nanoparticle materials can be used to generate optically relevant architectures, enabling a significant step in the development of self-assembly as a materials fabrication tool for integrated optical devices.

Deformation and mineralizing fluid circulation of gold-silver-bearing quartz veins in the Yushishan gold deposit, Altyn Mountain, northwestern China

Understanding the coupled process of deformed microstructure and fluid evolution of ore veins therefore provides insight into processes that influence mineralization distribution and its mechanism. Gold is often developed in quartz veins in many gold deposits. This paper presents detailed evidence for solid deformation, hydrothermal fluid, and mineralization in a fault-controlled gold-silver-bearing quartz vein from the Yushishan gold deposit, Altyn Mountain, NW China. Macro-and microstructure combined quartz crystal preferred orientation (CPO) unravel the ductile–brittle transition deformation of quartz veins formed at the deep crustal level ca. 9 ∼ 13 km and the deformation temperature ranging between 180 ∼ 381 °C. The homogenization temperatures and salinities of fluid inclusions change slightly, while the trapping pressure of fluid inclusions has a large fluctuation of ca. 125 ∼ 275Mpa. HO isotopes and the composition of fluid inclusions decipher the source of ore-forming fluid mainly related to the regional magmatic-metamorphic event. Combined with the fluid immiscibility that is evidenced by different types of fluid inclusion coexistence characteristics and the pH increase induced by CO2 degassing in an inhomogeneous fluid system, it is suggested that an obvious fluid overpressure and rapid decompression occur during Au deposition from the quartz vein. The seismically fractured opening and healing of rocks during ductile–brittle deformation controls the formation of the mineralization and fluid circulation. There has positive feedback between the fluid overpressure evolution, strain localization and mineralization through time. The channelized and circulated fluid flow triggered extensive veining, mineral growth, and connections with fluid reservoirs.

In situ crosslinking-assisted perovskite grain growth for mechanically robust flexible perovskite solar cells with 23.4% efficiency

•Enhanced the crystallization of flexible perovskite •Reduced Young’s modulus of perovskite film •Exhibited record efficiency •Exhibited excellent mechanical stability Flexible perovskite solar cells (pero-SCs) are the best candidates to complement silicon solar cells in the photovoltaic market. However, their power conversion efficiencies (PCEs) and mechanical stability are far behind the industry standards because of the uncontrollable growth of perovskites on plastic substrates and intrinsically high Young’s modulus. We explored an in situ crosslinking bis((3-methyloxetan-3-yl) methyl) thiophene-2,5-dicarboxylate along with perovskite growth, and its coordination ability and crosslinking temperature enabled the fine regulation of the quality of perovskite in real time. The resultant perovskite film exhibits an enlarged grain size, compact stacking, and a preferential crystal orientation. Moreover, the crosslinked elastomer polymer gathered at the perovskite grain boundaries can effectively release the mechanical stress. As a result, the flexible pero-SC based on this perovskite film achieved a record PCE of 23.4% (certified 22.9%), which is comparable with that of the rigid device. Importantly, the flexible pero-SCs also display a robust bending durability. Flexible perovskite solar cells (pero-SCs) are the best candidates to complement silicon solar cells in the photovoltaic market. However, their power conversion efficiencies (PCEs) and mechanical stability are far behind the industry standards because of the uncontrollable growth of perovskites on plastic substrates and intrinsically high Young’s modulus. We explored an in situ crosslinking bis((3-methyloxetan-3-yl) methyl) thiophene-2,5-dicarboxylate along with perovskite growth, and its coordination ability and crosslinking temperature enabled the fine regulation of the quality of perovskite in real time. The resultant perovskite film exhibits an enlarged grain size, compact stacking, and a preferential crystal orientation. Moreover, the crosslinked elastomer polymer gathered at the perovskite grain boundaries can effectively release the mechanical stress. As a result, the flexible pero-SC based on this perovskite film achieved a record PCE of 23.4% (certified 22.9%), which is comparable with that of the rigid device. Importantly, the flexible pero-SCs also display a robust bending durability.

Anisotropic tensile behavior of laser powder-bed fusion made Ti5553 parts

Directional heating during metal additive manufacturing promotes the growth of a columnar-grained microstructure along the building direction with a preferred crystal orientation, which results in anisotropy of properties. In this work, the anisotropy of laser powder bed fused Ti-5553 metastable β titanium alloy components are investigated. Samples printed in the normal (vertically printed), and parallel (horizontally printed) orientations to the building direction were subjected to quasi-static uniaxial tensile tests. In comparison, samples printed parallel to the building direction exhibit a significantly higher ultimate strength of 846 ± 6 MPa, whereas the samples printed normal to the building direction reached 780 ± 10 MPa. Fracture initiation and propagation were investigated using interrupted tensile testing. The fracture path of partially fractured specimens reveals the development of slip bands oriented at a 45 ± 5° angle with respect to the loading direction, which promoted fracture by coalescence of aligned pores. Electron backscatter diffraction results indicate that the grain boundaries act as favorable nucleation sites for fracture initiation, particularly when they align perpendicular to the loading direction. Conversely, fracture in samples printed parallel to the building direction was predominantly transgranular, which is expected to be a major contributing factor to the higher strength observed.

Improved Reversal Tolerant Properties of IrOX as an Anode Electrocatalyst in Proton Exchange Membrane Fuel Cells

Voltage reversal is a severe issue in proton exchange membrane fuel cells (PEMFCs), which can be overcome by adding oxygen evolution electrocatalysts (OER) based on iridium oxide (IrOX) to the anode catalyst layer. However, the crystal structure and antireversal properties of such anode materials have been rarely investigated. Herein, we report amorphous IrOX and explore the transformation of crystal structure under heat treatment to examine their antireversal performance in PEMFCs. It is found that heat treatment results in larger catalyst particles which consequences lower OER activity; however, it shows better voltage reverse tolerance (132.2 min). These investigations demonstrate that a balance is crucial between activity and durability in antireversal properties for PEMFCs. Physical characterizations reveal that improved stability and reversal tolerance is attributed to crystallinity and preferred orientation of IrOX crystals as well as existence of amorphous and crystalline IrOX. This work proposes a attempt to use the mixed phase IrOX in the antireversal anode catalyst and highlights the role of corresponding particle size and durability characteristics for the long-term durability of PEMFCs.

Ultralow thermal conductivity and enhanced thermoelectric properties in a textured (Ca0.35Sr0.2Ba0.15Na0.2Bi0.1)3Co4O9 high-entropy ceramic

A novel layered (Ca0.35Sr0.2Ba0.15Na0.2Bi0.1)3Co4O9 high-entropy ceramic is prepared for the first time by the traditional solid-state reaction. The XRD, SEM-EDS and TEM data exhibit that the multi-component cations can be introduced into the Ca site to form a single-phase and homogeneous solid solution with highly preferential crystal orientation and multi-scale structural defects. The textured high-entropy ceramic, compared to the pristine Ca3Co4O9 sample, shows a significantly increased electrical conductivity due to the higher carrier mobility derived from the c-axis selective orientation, and obtains an enhanced power factor of 0.27 mW·m−1·K−2. Besides, high entropy induced multi-dimensional lattice defects can act as the phonon scattering centers to effectively suppress the lattice thermal conductivity, and achieves an ultralow thermal conductivity of 0.87 W·m−1·K−1 as well as a peak figure-of-merit of 0.3 at 973 K, which is about 2.5 times larger than that of Ca3Co4O9. Our work deeply reveals the impact of the microstructure on thermoelectric properties in a high-entropy ceramic, which may help to advance the understanding and design of high-entropy thermoelectric materials.

Sr2TiSi2O8 (STS) Polar Glass-Ceramics: Effect of Na2O and CaO Additions in the Parent Glass on the Crystallization Mechanism and on the Piezoelectric Properties

Glass-ceramics containing pyroelectric Sr2TiSi2O8 (STS) crystals are produced from parent glasses of compositions STS + 0.8 SiO2 + (0.2 − x) Na2O + x CaO, with x = 0; 0.05; 0.10; and 0.15. The aim of this work is to investigate the effect of the additions to the stoichiometric STS composition on the crystallization mechanisms and on the piezoelectric properties of the glass-ceramic. The DSC analyses evidence that the glass transition temperatures Tg, the onset temperature of the crystallization peak To and the temperature Tc of the maximum of this peak increase with the CaO/Na2O ratio. On the basis of the DSC data, the crystallization of the parent glass samples was operated by thermal treatment. The observation of the cross-sections of the heat-treated samples highlights that the competition between the surface and volume crystallization mechanisms is influenced by the CaO/Na2O ratio and the temperature. For all the samples, the XRD analyses performed on the surfaces as obtained after the crystallization treatment evidenced a preferential orientation of the STS crystals with the plans (00l) parallel to the surface. The XRD analyses performed after grinding the surface show that only the surface crystallized layers are preferentially oriented. Moreover, changes in preferential orientation to plans (202) or (201) are observed over the depth, depending on the composition and the temperature of the thermal treatment. These changes influence the polarization of the surface crystallized layer and, consequently, its piezoelectric charge coefficient d33. The highest values of d33 were measured on the glass-ceramic samples exhibiting mainly a (202) preferential orientation over their thickness.

A boost of thermoelectric generation performance for polycrystalline InTe by texture modulation.

The new rising binary InTe displays advantageously high electronic conductivity and low thermal conductivity along the [110] direction, providing a high potential of texture modulation for thermoelectric performance improvement. In this work, coarse crystalline InTe material with a high degree of texture along the [110] direction was realized by the oriented crystal hot-deformation method. The coarse grains with high texture not only maintain the preferred orientation of the zone-melting crystal as far as possible, but also greatly depress the grain boundary scattering, thus leading to the highest room temperature power factor of 8.7 μW cm-1 K-1 and a high average figure of merit of 0.71 in the range of 300-623 K. Furthermore, the polycrystalline characteristic with refined grains also promotes the mechanical properties. As a result, an 8-couple thermoelectric generator module consisting of p-type InTe and commercial n-type Bi2Te2.7Se0.3 legs was successfully integrated and a high conversion efficiency of ∼5.0% under the temperature difference of 290 K was achieved, which is comparable to traditional Bi2Te3 based modules. This work not only demonstrates the potential of InTe as a power generator near room temperature, but also provides one more typical example of a texture modulation strategy beyond the traditional Bi2Te3 thermoelectrics.

Post‐Annealing Treatment on Hydrothermally Grown Antimony Sulfoselenide Thin Films for Efficient Solar Cells

Herein, antimony sulfoselenide (Sb2(S, Se)3) thin‐film solar cells are fabricated by a hydrothermal method followed by a post‐deposition annealing process at different temperatures and the impact of the annealing temperature on the morphological, structural, optoelectronic, and defect properties of the hydrothermally grown Sb2(S, Se)3 films is investigated. It is found that a proper annealing temperature leads to high‐quality Sb2(S, Se)3 films with large crystal grains, high crystallinity, preferred crystal orientation, smooth and uniform morphology, and reduced defect density. These results show that suppressing deep‐level defects is crucial to enhance solar cell performance. After optimizing the annealing process, Sb2(S, Se)3 solar cells with an improved power conversion efficiency 2.04 to 8.48% are obtained.

Crustal Anisotropy in the Martian Lowlands From Surface Waves

AbstractThe largest seismic event ever recorded on Mars, with a moment magnitude of 4.7 ± 0.2, is the first event to produce both Love and Rayleigh wave signals. We measured their group velocity dispersion between about 15 and 40 s period and found that no isotropic depth‐dependent velocity model could explain the two types of waves wave simultaneously, likely indicating the presence of seismic anisotropy. Inversions of Love and Rayleigh waves yielded velocity models with horizontally polarized shear waves traveling faster than vertically polarized shear waves in the top 10–25 km. We discuss the possible origins of this signal, including the preferred orientation of anisotropic crystals due to shear deformation, alignment of cracks, layered intrusions due to an impact, horizontal layering due to the presence of a large‐scale sediment layer on top of the crust, and alternation of sedimentation and basalt layers deposits due to large volcanic eruptions.

Substrate effect on the electrochemical capacity pattern (ECP) of PbS

Different metals (Zn, Cu, Pb) were electrodeposited on indium tin oxide (ITO/metal). ITO/metal was used as a substrate for ZnO and PbS deposition, and finally the PbS surface was encapsulated with ZnS. The electrochemical capacitance, CEC, of each thin layer was calculated from the cyclic voltammetry data and plotted against the applied potential. The plots showed different electrochemical capacity pattern (ECP) for PbS with different metal substrates. It seems that these patterns are effectively controlled by the ECP of the metal substrates. Also, the PbS CEC values were calculated from electrochemical impedance spectroscopy, EIS, to be compared with PbS CEC values obtained from cyclic voltammetry. The results of this comparison were completely consistent with each other and confirm different metal as a substrate effects on the PbS and may lead to a structure with different ECP. In the X-ray diffraction pattern, the presence of different preferential orientation of metal crystals was confirmed, which have been leaded to the formation of PbS deposits with different ECP.

Honeycomb-Type TiO2 Films Toward a High Tolerance to Optical Paths for Perovskite Solar Cells.

Given the advantages of high power conversion efficiencies (PCEs), antisolvent-step free production, and suitability for device production in ambient conditions, perovskite solar cells (PSCs) based on ionic-liquid solvents have attained particular research interest. To further improve device performance, light management could be optimized to increase light harvesting in the perovskite layer. Here, ordered honeycomb-like TiO2 (Hc-TiO2 ) structures with a periodicity of around 450 nm were fabricated through a sacrificial template method. With this photonic crystal structure, the control to light flow and the confinement effect for perovskite growth were achieved simultaneously in the Hc-TiO2 , leading to improved light absorption as well as preferred crystal orientation. Furthermore, a reduced trap-state density and a well-aligned energy level induced by the perovskite/pore interlayer facilitated the charge-carrier extraction from the perovskite layer to electron transport layer. As a result, the structured devices performed better than the planar cells. And the angular dependent J-V sweeps show that the structured device reserved 76 % of its initial short circuit current density (Jsc ), whereas the planar cell showed more than a half loss under the incident light of 40°, demonstrating a reduced downward trend in Jsc with the presence of photonic crystal structures. This occurrence also suggests that the structured PSCs in this work have a high tolerance to optical path changes.

Interfacial charge transfer effects of α-Fe2O3/Cu2O heterojunction and enhancement mechanism of its photocatalytic oxidation

In order to construct Cu2O based heterostructures with high efficiency of interfacial charge transfer and clarify the enhancing mechanism of its photocatalytic performance for degrading antibiotics, and reveal the characteristics of band reconstruction and the photocatalytic reaction path, the α-Fe2O3/Cu2O heterojunction was established based on hydrothermal method. The crystal plane structure, morphological state, photoelectric conversion properties and photocatalytic degradation kinetics of α-Fe2O3/Cu2O heterojunction were revealed by XRD, XPS, UV-Vis, BET, SEM, TEM and RSM, and the reconstruction principles of bandgap formations of heterojunction were analyzed by the density function theory. The reaction intermediates of levofloxacin were distinguished with HPLC-MS/Ms, and the reactive sites and photocatalytic oxidation paths of levofloxacin were clarified from the frontier electron density calculation. It turned out that the constructed α-Fe2O3/Cu2O heterojunction emerged high energy (111) preferred crystal plane orientation and significantly enhanced the specific surface area and visible spectral excitation efficiency. The micromorphologies of Cu2O, M1-Cu2O, M2-Cu2O and M3-Cu2O crystals were cube, irregular polyhedron and approximate sphere, respectively. The introduction of Fe 3d hybrid orbital in α-Fe2O3/Cu2O heterojunction widened the band gap of Cu2O microcrystals, resulting in the migration of spectral absorption edging to high energy level and causing blueshift. Photogenerated superoxide radicals and hydroxyl radicals were the dominant active species for photocatalytic oxidation of levofloxacin. The removal rate of levofloxacin by α-Fe2O3/Cu2O heterojunction could still reach more than 70% after eight cycles and show high material durability. The ring opening reaction process and decarboxylic reaction of quinolone group and piperazine side chain were the main pathways for photocatalytic oxidation of levofloxacin. This study systematically revealed the interfacial charge transfer characteristics and photocatalytic reaction mechanism of α-Fe2O3/Cu2O heterojunction.

Slowing the hot‐carrier cooling by an organic small molecule in perovskite solar cells

AbstractHarvesting hot carriers (HCs) before thermalizing to the perovskite crystal lattice is very promising for advancing the efficiency of perovskite solar cells (PSCs) towards the Shockley–Queisser limit. Thus, it is very crucial to slow down the HCs cooling process in lead halide perovskites. Herein, we investigated the HCs cooling dynamics of perovskite films in the presence of an organic small molecule, 2,5‐thiophenedicarboxylic acid (TDCA). We found that adding TDCA into perovskite films can efficiently retard HCs cooling process, which favors extracting the excess energies of HCs through carrier transport layers and reducing electron–hole recombination, resulting in enhanced performance in TDCA modified device. Moreover, TDCA can effectively passivate unsaturated Pb2+ defects of perovskite films while promoting a preferential crystal orientation. Consequently, the PSCs efficiency is enhanced to 22.85% (TDCA) from 19.96% (control). These findings provide important insight for understanding HCs transfer dynamics and developing next‐generation perovskite‐based HCs optoelectronic devices.image

Elucidating the Origins of High Preferential Crystal Orientation in Quasi-2D Perovskite Solar Cells.

Incorporating large organic cations to form2Dand mixed 2D/3D structures significantly increases the stability of perovskite solar cells. However, due to their low electron mobility, aligning the organic sheets to ensure unimpeded charge transport is critical to rival the high performances of pure 3D systems. While additives such as methylammonium chloride (MACl) can enable this preferential orientation, so far, no complete description exists explaining how they influence the nucleation process to grow highly aligned crystals. Here, by investigating the initial stages of the crystallization, as well as partially and fully formed perovskites grown using MACl, the origins underlying this favorable alignment are inferred. This mechanism is studied by employing 3-fluorobenzylammonium in quasi-2D perovskite solar cells. Upon assisting the crystallization with MACl, films with a degree of preferential orientation of 94%, capable of withstanding moisture levels of 97% relative humidity for 10h without significant changes in the crystal structure are achieved. Finally, by combining macroscopic, microscopic, and spectroscopic studies, the nucleation process leading to highly oriented perovskite films is elucidated. Understanding this mechanism will aid in the rational design of future additives to achieve more defect tolerant and stable perovskite optoelectronics.

N -(2-aminoethyl) Acetamide Additive Enables Phase-Pure and Stable α-FAPbI3 for Efficient Self-Powered Photodetectors.

Formamidinium-lead triiodide (FAPbI3 ) perovskite is considered as one of the most promising perovskite materials for high-performance photodetectors because of its narrow bandgap and superior thermal stability. Nevertheless, to realize efficient carrier transport and highly performing photodetectors, it imposes the requirement of fabricating α-FAPbI3 with pure phase, preferred crystal orientation, large grain size, and passivated interface, which still remains challenging. Here, a facile strategy based on additive engineering to obtain pure-phase FAPbI3 perovskite films by introducing N-(2-aminoethyl) acetamide into perovskite precursors is reported. The formation of chemical bond and hydrogen bond between N-(2-aminoethyl) acetamide and perovskite reduces the potential barrier in the phase-transition process from an intermediate yellow phase to a final black phase, passivates the defects of the film, and leads to a high-quality and phase-pure α-FAPbI3 perovskite. A self-powered photodetector based on the as-fabricated FAPbI3 film exhibits a maximum responsivity of 0.48 A W-1 at 700nm with a peak external quantum efficiencyof 95% at 440nm. Moreover, the optimized device remains 83% of the initial performance after 576h storage at ambient condition. This work provides a simple and feasible scheme for the preparation of high-quality phase-pure α-FAPbI3 perovskite and associated devices.

Improved functional fatigue resistance of single crystalline NiTi micropillars with uniformly oriented Ti3Ni4 precipitates

Superelasticity is one promising functional property of shape memory alloys. To utilize superelasticity in application, sufficient fatigue life (i.e., for functional fatigue) during the mechanical cyclic phase transformation is one of the most important issues to be solved. Here, we successfully manufactured the NiTi single crystalline micropillars which exhibit different crystalline orientations, with uniformly oriented Ti3Ni4 precipitates and few defects. The mechanical properties of these NiTi single crystalline micropillars were systematically investigated. The NiTi single crystalline micropillar with the [20 2_ 9]B2 (B2: parent phase) crystalline orientation showed quite stable superelasticity during the cyclic compression, which sustained more than 107 phase transformation cycles with only 8% decay (from 5.1% for the 1st cycle to 4.7% for the 107 cycle). Meanwhile, as the cyclic number increased, the stress-strain curves became more stable, and the critical stress for inducing martensitic transformation (from 574 MPa for the 1st cycle to 312 MPa for the 107 cycle) and the stress hysteresis (from 7.2 MJ/m3 for the 1st cycle to 3.0 MJ/m3 for the 107 cycle) during the loading-unloading processes both decreased. By analyzing the dislocation plasticity assisted by cyclic martensitic transformations, we show that specific martensite variants are selected biasedly by the interplay of external load and inhomogeneous stress field caused by uniformly oriented Ti3Ni4 precipitates, which lead to a number of slip systems effectively impeded by the precipitates. This study opens a new avenue to develop fatigue resistant shape memory alloy through tailoring the aligned precipitates and preferred crystal orientation.

Ultrafast-laser powder bed fusion of oxygen-deficient Nb2O5 ceramics with highly improved electrical properties

In this work, Nb2O5 layers with highly improved electrical properties respect to pristine material have been produced by ultrafast-laser powder bed fusion process. The conditions required for producing uniform and compact layers of Nb2O5 from powder material have been studied and optimized. It has been established that ultrafast-laser irradiation, performed in air at room temperature, leads to the formation of dense Nb2O5 layers with the high temperature monoclinic crystal structure (H-Nb2O5) but oxygen deficient. The layers show a preferential crystal orientation with the short axis of the monoclinic structure lying in the structure plane. This preferential orientation can be controlled by the laser irradiation conditions. Anisotropic resistivity has been observed as a consequence of the induced microstructure, while the overall material resistivity is decreased by more than eight orders of magnitude due to the oxygen deficiency. These results indicate that it is feasible to use ultrafast laser processing to promote high-temperature non-stoichiometric niobium oxide phases in a few seconds and with low energy consumption. The highly improved electrical properties of the laser irradiated Nb2O5 layers are extremely interesting for different electronic and sensing applications.