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The amorphous Ti–Ni-Hf thin films with the specific compositions were prepared from single Ti–Ni-Hf alloy target by adjusting processing parameters of direct current magnetron sputtering deposition. Prior to the crystallization, a glass transition occurred in the present Ti–Ni-Hf thin films. The annealed Ti–Ni-Hf thin films were characterized by the nano-crystalline. With the annealing temperature increasing, the grain size firstly increased and then decreased owing to the presence of (Ti,Hf)2Ni precipitate. Two endothermic and exothermic peaks corresponding to B19’⇌B2 martensitic transformation in heating and cooling curves were observed for the Ti–Ni-Hf thin films with the lower annealing temperature and shorter annealing time, which was closely related to the inhomogeneous composition. However, the Ti–Ni-Hf thin films annealed at higher annealing temperature and longer annealing time showed the single stage B19’⇌B2 martensitic transformation. In addition, the martensitic transformation temperatures firstly increased and then decreased with the annealing temperatures rising.

The microstructure features, martensitic transformation behavior and mechanical/functional properties of Ti–V–Al alloy were tailored by changing rare element Y content in the present investigation. The results showed that Y doping resulted in the grain refinement and formation of Y-rich phase mainly distributing along grain boundary in Ti–V–Al alloys. The martensitic transformation temperatures of Ti–V–Al alloys slightly increased due to the variation of matrix composition induced by the presence of Y-rich phase. The mechanical and functional properties of Ti–V–Al alloys doped moderate Y addition were significantly improved, which can be ascribed to grain refinement, solution strengthening and precipitation strengthening. The 1.0 ​at.%Y-doped Ti–V–Al alloy exhibited the highest ultimate tensile stress of 912 ​MPa and largest elongation of 17.68%. In addition, it was found that the maximum recoverable strain of 5.42% can be obtained in Ti–V–Al alloy with adding 1.0 ​at.%Y, under the pre-strain of 6% condition, which is enhanced by approximate 0.6% than that of Ti–V–Al alloy without Y addition.

Interlayer excitons have been extensively studied in monolayer transition metal dichalcogenide (TMD) heterobilayers mainly due to the long lifetime, which is beneficial for a wide range of optoelectronic applications. To date, the majority of investigations of interlayer excitons in TMD heterobilayers have been focusing on the geometric arrangement of structures, spin-valley lifetime, and interlayer valley excitons with interlayer hopping rules. Nevertheless, interlayer excitons in TMD heterobilayers strongly depend on the local atomic registry and coupling strength, which increase the complexity of the device fabrication. Here, we report pronounced interlayer exciton emission in two-dimensional (2D) perovskite/monolayer TMD heterostructures without the need of thermal annealing or specific geometric arrangements, and the interlayer exciton emission is rather general among 2D perovskites and monolayer TMDs. Such interlayer exciton emission completely dominates the emission spectrum at 78 K regardless of the stacking sequence, suggesting the robust interlayer coupling in 2D perovskite/monolayer TMD heterostructures. Furthermore, the interlayer exciton emission shows a large blue-shift with increasing laser intensity due to the repulsive dipole-dipole interaction and can persist above 220 K. Importantly, the interlayer exciton emission also possesses robust circular polarization in chiral 2D perovskite/monolayer WSe

Lake waters often act as important methane sources for global greenhouse gas emission, but it would be more complex as lakes are regulated by rivers. In this study, seasonal variations of dissolved and emitted methane in the Poyang Lake, the largest freshwater lake in China, are investigated based on a specially designed monitoring. As a typical subtropical linking-to-river lake, the Poyang shows characteristics of the “lake” in wet season and the “river” in dry season alternatively over a year. Consequently, CH4 flux from the Poyang Lake to the Yangtze River closes to the highest in January due to concentrated dissolved CH4 and “river” effects in dry season, while CH4 flux to the atmosphere falls to the lowest in July because of intensified CH4 oxidization and diluted dissolved CH4 as well as “lake” effects in wet season. Overall, CH4 fluxes from Poyang Lake to the atmosphere and to the Yangtze River were 19 and 0.35 Gg CH4 yr−1, respectively. The Three Gorges Dam, the world’s largest dam in the Yangtze River, would further intensify this pattern, enhancing the transformation between “lake phase” and “river phase”. This study also provides the paradigm for CH4 budget from other large lakes in similar situations around the world.

Supercritical carbon dioxide fracturing not only enhances fossil hydrogen production better than hydraulic fracturing, but also alleviates water consumption and storages some carbon dioxide in reservoirs. In this study, a numerical simulation model for calculating the temperature and pressure within a fracture during supercritical carbon dioxide fracturing was established based on rock mechanics, fluid mechanics, thermodynamics, and heat transfer. Moreover, the effects of impact of in-situ stress of reservoir, reservoir temperature, carbon dioxide temperature at the bottom of the well and injection rate on temperature and pressure in the fracture are analyzed based on this new model. The results show that the temperature and pressure of carbon dioxide in the fracture are constantly changing during the fracturing, due to the propagation of the fracture, which makes the temperature and pressure in the fracture unable to reach a steady state. The effect of supercritical carbon dioxide fracturing in reservoirs with higher temperature and lower in-situ stress is better, and higher injection temperatures and smaller injection rates should be chosen in order for carbon dioxide to quickly reach the supercritical state.

Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted growing attention recently due to their naturally formed quantum-well structure, unique photoelectric properties and better environmental stability compared to three-dimensional perovskites. The reduced screening and enhanced Coulomb interaction in 2D perovskites result in the formation of excitonic complexes. While the properties of free excitons have been well investigated, studies on biexcitons remain elusive. Here, we report on the biexcitons in 2D (iso-BA)2PbI4 (BA=C4H9NH3) crystals. The biexciton emission can be observed under a very low excitation power density of 6.4 W/cm2 at 78 K. The biexciton exhibits a large biexciton binding energy of 46 meV due to the large exciton binding energy of (iso-BA)2PbI4. Furthermore, the biexcitons exhibit a favorable polarization orientation, resulting in different anisotropy between biexcitons and excitons. Our findings would motivate more studies on biexcitons in 2D perovskites and pave the way for exploiting the many-body physics for biexciton lasing and optical storage devices.

Surface depletion field would introduce the depletion region near surface and thus could significantly alter the optical, electronic and optoelectronic properties of the materials, especially low-dimensional materials. Two-dimensional (2D) organic—inorganic hybrid perovskites with van der Waals bonds in the out-of-plane direction are expected to have less influence from the surface depletion field; nevertheless, studies on this remain elusive. Here we report on how the surface depletion field affects the structural phase transition, quantum confinement and Stark effect in 2D (BA)2PbI4 perovskite microplates by the thickness-, temperature- and power-dependent photoluminescence (PL) spectroscopy. Power dependent PL studies suggest that high-temperature phase (HTP) and low-temperature phase (LTP) can coexist in a wider temperature range depending on the thickness of the 2D perovskite microplates. With the decrease of the microplate thickness, the structural phase transition temperature first gradually decreases and then increases below 25 nm, in striking contrast to the conventional size dependent structural phase transition. Based on the thickness evolution of the emission peaks for both high-temperature phase and low-temperature phase, the anomalous size dependent phase transition could probably be ascribed to the surface depletion field and the surface energy difference between polymorphs. This explanation was further supported by the temperature dependent PL studies of the suspended microplates and encapsulated microplates with graphene and boron nitride flakes. Along with the thickness dependent phase transition, the emission energies of free excitons for both HTP and LTP with thickness can be ascribed to the surface depletion induced confinement and Stark effect.

The effect of the substitution of Pt for Cu on the microstructure and martensitic transformation behaviors of Ti–Ni–Cu alloys was investigated systematically. The solution-treated Ti–Ni–Cu–Pt alloys were found to consist of the B19 martensite and Ti2(Ni,Cu,Pt) phases at room temperature. The (011) compound twin was more frequently observed than the (111) type I twin in the Ti–Ni–Cu–Pt alloys owing to the lower shear strain and shear angle of the (011) compound twin during the transformation process. During heating, the lower temperature single B19 martensite transformed in one stage into high-temperature B2 austenite. Conversely, the B2 austenite was transformed directly into B19 martensite during cooling. As the Pt content increased from 1.0 at.% to 3.0 at.%, the transformation temperatures first decreased and then increased. In addition, a narrower thermal hysteresis and perfect thermal cycling stability can be obtained by tailoring the Pt content. The excellent thermodynamic characteristics can be attributed to the lower frictional work and good geometric compatibility.

Energy crisis due to the depletion of fossil fuel as well as the increased population has stimulated researchers to search for new energy resources and energy storage and conversion systems, including fuel cells, electrolyzers and metal–air batteries. Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are two reactions that dominate the overall performance of these devices. However, the sluggish kinetics of these two reactions still impedes the practical application of these devices. Therefore, electrocatalysts, especially non-noble metal oxides are needed to expedite the reactions. Perovskite oxides, as a member of the mixed metal oxide family, show promising electrocatalytic performance toward both ORR and OER. However, there are only a few articles regarding the recent progress of perovskites as bifunctional electrocatalysts till now. In this mini-review, we summarize the recent research status and progress of perovskite oxides as electrocatalysts for ORR/OER, including the basic mechanism behind the catalytic reactions, different approaches to synthesize perovskites as well as the various strategies that researchers have developed to promote their electrocatalytic activities. Besides, the related theoretical calculation method, density functional theory (DFT), which is used to understand the mechanism behind these reactions, has also been discussed. It is believed that this mini-review can not only offer researchers guidance to synthesize perovskite oxides as demanded, but also provide researchers more insights into how to rationally design new perovskite-based catalysts with improved bifunctional electrocatalytic properties.

In the present study, the extensive efforts had been made to attain the higher-quality Zr Cu based ribbons by optimizing the fabrication process. Under the same preparation conditions, the as-spun Zr Cu based ribbons with the different amorphous state can be obtained by tailoring the chemical compositions. The microstructure of the as-spun Zr50Cu50 ribbon was featured with the amorphous matrix embedded with the B2 crystalline and the superior mechanical properties can be achieved as a result of the martensitic transformation induced by stress during deformation. The partial substitute of Cu by Ni and Co enhanced the ability of forming the amorphous Zr-Cu-Ni-Co ribbons and the size of the B2 crystalline gradually became smaller. The reduction of B2 crystalline in the amorphous matrix led to the slight decrease in the mechanical properties of the as-spun Zr Cu based ribbons. However, the microstructure of the annealed Zr Cu based ribbons was characterized by the nano-scale grain. Meanwhile, the nano-scale Cu10Zr7 precipitates distributed in the nanograin. The grain refinement and precipitation strengthening contributed to the superior mechanical properties of the annealed Zr Cu based ribbons.

In the present study, the Ti-Ni-Zr alloy ribbons with the various Zr contents were fabricated at the optimum process conditions. The crystallization process and the effect of the following annealing treatments on the microstructural evolution, martensitic transformation behavior, mechanical properties and shape memory effect of the annealed Ti-Ni-Zr alloy ribbons were investigated systematically. The results revealed that the phase constituents were dependent on the Zr contents, and can be tailored by the annealing treatment. The λ1 precipitate existed in all annealed Ti-Ni-Zr alloy ribbons and NiZr phase appeared only in the annealed Ti-Ni-Zr alloy ribbons with the Zr content more than 25 at.%. With the annealing temperatures increasing, the martensitic transformation temperature increase. And the Ti-Ni-Zr alloy ribbons with the higher Zr content showed the relatively lower transformation temperatures owing to the presence of the NiZr precipitate. The nano-scale λ1 precipitate and NiZr phase can enhance the matrix strength and improve the mechanical properties, while the appearance of the lots of the NiZr phase would deteriorate the shape memory effect. Among, the annealed Ti-Ni-Zr alloy ribbon showed the excellent combination of the higher transformation temperatures, superior mechanical and strain recovery characteristics. In summary, the evolution of the microstructure containing the martensitic/austenitic state, type/size of the precipitate, and distribution state of the precipitate resulted in the changing of the martensitic transformation, mechanical properties and shape memory effect.

The diversification of data types and the explosive increase of data size in the information era continuously required to miniaturize the memory devices with high data storage capability. Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for flexible and transparent electronic and optoelectronic devices with high integration density. Multistate memory devices based on TMDs could possess high data storage capability with a large integration density and thus exhibit great potential applications in the field of data storage. Here, we report the multistate data storage based on multilayer tungsten diselenide (WSe2) transistors by interface engineering. The multiple resistance states of the WSe2 transistors are achieved by applying different gate voltage pulses, and the switching ratio of the memory can be as large as 105 with high cycling endurance. The water and oxygen molecules (H2O/O2) trapped at the interface between the SiO2 substrate and WSe2 introduce the trap states and thus the large hysteresis of the transfer curves, which leads to the multistate data storage. In addition, the laminated Au thin film electrodes make the contact interface between the electrodes and WSe2 free of dangling bond and Fermi level pinning, thus giving rise to the excellent performance of memory devices. Importantly, the interface trap states can be easily controlled by a simple oxygen plasma treatment of the SiO2 substrate, and subsequently, the performance of the multistate memory devices can be manipulated. Our findings provide a simple and efficient strategy to engineer the interface states for the multistate data storage applications and would motivate more investigations on the trap state-associated applications.

Energy depletion caused by the consumption of fossil fuels due to increasing population and economic growth has stimulated intense research on electrochemical energy storage systems, including fuel cells and metal-air batteries. Oxygen electrocatalysis, including both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), dominates the performance of these electrochemical energy systems. However, the sluggish kinetics of these two reactions still limits their performance and even the commercialization of these electrochemical energy storage systems. Therefore, development of non-precious metal-based oxygen catalysts, especially with bifunctionality for both OER and ORR, is greatly demanded. In this report, polymer-assisted approach has been employed to synthesize LaCoO3-based perovskite nanoparticles, which interconnected together to form porous network structures. X-ray diffraction indicated that replacement of Co with Ni would lead to a lattice expansion due to larger ionic radius of Ni3+ as compared to that of Co3+. The electrocatalytic activity of these materials in 0.1 M KOH aqueous solution showed that ORR performance of LaCoO3 can be improved through incorporation of Ni into the B-site while their OER performance will also be enhanced which renders these perovskite oxides to exhibit better bifunctional electrocatalytic activity for both OER and ORR. The enhanced performance with Ni-doping might be due to the synergistic effect from the two transition metals as a result of the formation of new redox couples Ni3+/Ni2+ as well as the higher Co3+/Co2+ ratio, which could promote adsorption of oxygen on the catalytic surface with improved the Co O bond strength. Our study not only introduces polymer-assisted method to prepare network structured perovskite nanoparticles, but also highlights the importance of B-site metal doping in perovskites as a simple strategy to enhance their bifunctional oxygen catalytic activities.

Two-dimensional (2D) Ruddlesden–Popper perovskites have attracted great interest for their promising applications in high-performance optoelectronic devices owing to their greatly tunable band gaps, layered characteristics, and better environmental stability over three-dimensional (3D) perovskites. Here, we for the first time report on photodetectors based on few-layer MoS2 (n-type) and lead-free 2D perovskite (PEA)2SnI4 (p-type) heterostructures. The heterojunction device is capable of sensing light over the entire visible and near-infrared wavelength range with a tunable photoresponse peak. By using few-layer graphene flakes as the electrical contact, the performance of the heterostructures can be improved with a responsivity of 1100 A/W at 3 V bias, a fast response speed of ∼40 ms under zero bias, and an excellent rectification ratio of 500. Importantly, the quantum efficiency can achieve 38.2% at zero bias, which is comparable or even higher than that of 3D perovskite/2D material photodetectors. Impor...

Developing low-cost and highly efficient oxygen electrocatalysts for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) has become one important issue recently due to the sluggish kinetics of these two reactions, which require high overpotentials and thus high energy input. Perovskite oxides have emerged as a new class of highly efficient non-precious metal catalysts for oxygen electrocatalysis in alkaline media. In this work, an IrO2-incorporated La0.8Sr0.2MnO3 composite has been developed as a novel bifunctional oxygen electrocatalyst using a polymer-assisted approach with a subsequent wet impregnation–calcination method. Due to the synergistic effect between the high ORR activity of La0.8Sr0.2MnO3 and the good OER activity of IrO2 as well as the improved electrochemically active surface area, the electrocatalytic activities of the composite for both the OER and ORR have been improved, compared with those of the pristine La0.8Sr0.2MnO3 (ΔE = 1.043 V), resulting in its enhanced bifunctionality (ΔE = 0.652 V) as an oxygen catalyst in alkaline solution, which is also superior to the reported state-of-the-art electrocatalysts. The stability test shows that after 1000 cycles of cyclic voltammetry (CV), there is only 15 mV positive shift for achieving a current density of 10 mA cm−2 in the OER and 17 mV negative shift to reach a current density of −1 mA cm−2 in the ORR, which indicates the good stability of the electrocatalyst (5 wt% IrO2 incorporated La0.8Sr0.2MnO3) in alkaline solution. Our study not only reports a new composite material as a bifunctional oxygen electrocatalyst, but also opens a new avenue to develop novel perovskite oxide-based electrocatalysts with enhanced bifunctional electrocatalytic activities.

The effect of substitution of Hf for Ti and Cu for Ni on microstructure, martensitic transformation behavior, mechanical properties and strain recovery characteristic of quaternary Ti-Ni-Cu-Hf alloys were investigated systematically. The results reveal that the B19→B19′ martensite transformation can be controlled by tailoring the Hf contents in Ti-Ni-Cu alloys. Although the B19 and B19′ martensite coexisted in Ti-Ni-Cu alloys with the minor Hf addition, only one-stage B2→B19′ transformation was observed in heating and cooling process. The transformation temperatures and transformation hysteresis can be adjusted by optimizing the chemical composition. In addition, the superior mechanical properties and shape memory effect can be achieved by tailoring the Hf can Cu contents. The maximum shape memory effect strain of 3.06% could be obtained in Ti47Ni44Cu6Hf3 alloy. And Ti45Ni44Cu6Hf5 alloy showed the largest tensile strength of 770 MPa. The present study provided the theoretical foundation for the potential application of the Ti-Ni-Cu-Hf alloys.

The precipitation of Ti3Ni4 phase during aging under the assist of the super-high stress in the Ni-rich Ti Ni alloy was investigated. The Ti3Ni4 precipitated in the matrix, accompanied by the generation of dislocations as a consequence of the applied super-high stress of several GPa level. The martensitic transformation behaviors changed from one-stage martensitic transformation to multiple-stage martensitic transformation with the changing of the applied stress level. The external applied super-high stress can result in the plastic deformation during aging, which can serve as the work hardening and further increase the micro-hardness, with an exception of the precipitation strengthening. In addition, the accumulation of larger numbers of dislocations and the generation of the localized stress field around the Ti3Ni4 precipitate during aging due to the applied stress should be a certain responsible for the evolution of superelasticity strain.

Two-dimensional (2D) organic–inorganic perovskites have recently undergone rapid development because of their unique optical properties, layered nature, and better environmental stability. Here, we report on a new type of 2D lead-free perovskite (C6H5C2H4NH3)2CsSn2I7 crystals with millimeter size and high field-effect hole mobility synthesized by a solution method. The excellent crystalline quality and phase purity have been verified by X-ray diffraction and low-temperature photoluminescence studies, while the X-ray photoelectron spectroscopy and energy-dispersive spectrometry measurements reveal the successful incorporation of Cs element into the resultant crystals and the absence of Sn4+ in the as-synthesized crystals. The as-synthesized crystals exhibit a high electrical conductivity and a high hole mobility up to 34 cm2·V–1·s–1 at 77 K. The crystals also show a high photoresponse resulting from the excellent optical properties and high electrical conductivity. Our findings show that the lead-free (C6H...

The quasi-uniform three-dimensional super high pressure was employed in the Ni-rich Ni-Ti alloy during aging treatment. Moreover, the effects of aging conditions (temperature, time and pressure) on the precipitation of Ti3Ni4 phase, martensitic transformation behavior and mechanical properties of the alloy were investigated systematically. The results revealed that the applied of super high pressure can provide the nuclear driving force of Ti3Ni4 precipitate and promote the precipitation of Ti3Ni4 phase. Unlike the applied of the uniaxial tensile or compressive stress, no significant preferred orientation of Ti3Ni4 precipitate was observed in the present stress-assisted aged Ni-Ti alloys as a consequence of the quasi-uniform three-dimensional stress. In addition, a certain number of dislocations generated in the aged Ni-Ti alloys due to the applied of super high pressure. However, the variations of the martensitic transformation behavior and mechanical properties are closely related to the evolution of the precipitation of Ti3Ni4 phase with the aging parameters and the generation of internal stress as well as the different thermodynamic state.

The microstructure, martensitic transformation behaviour, mechanical and strain recovery characteristics of the sintered Ti-Ni-Hf alloy composites reinforced by hybrid particles were investigated systematically, which had an instructive significance on the production of larger and complex high temperature shape memory alloy composite parts with the high mechanical and functional performance. The results showed that multiple particles including the in-situ TiB whisker, residual TiB2 phase and the (Ti,Hf)2Ni phase were observed in all samples. The gradually increased TiB2 content resulted in the continuous decrease of the transformation temperature as a result of mechanical and compositional effect. Nevertheless, the transformation temperature (MS) of the Ti-Ni-Hf alloy composite containing 1.5 wt% TiB2 was still above 100 °C, which can meet the requirement of high temperature applications. The hybrid reinforcements enhanced the matrix strength, and without sacrificing severely the compressive strain. In addition, the maximum completely recoverable strain of 6% can be obtained in the present composite.

Two-dimensional (2D) perovskites have recently attracted intensive interest for their great stability against moisture, oxygen, and illumination compared with their three-dimensional (3D) counterparts. However, their incompatibility with a typical lithography process makes it difficult to fabricate integrated device arrays and extract basic optical and electronic parameters from individual devices. Here, we develop a combination of solution synthesis and a gas–solid-phase intercalation strategy to achieve hexagonal-shaped 2D perovskite microplates and arrays for functional optoelectronics. The 2D perovskite microplates were achieved by first synthesizing the lead iodide (PbI2) microplates from an aqueous solution and then following with intercalation via the vapor transport method. This method further allows us to synthesize arrays of 2D perovskite microplates and create individual 2D perovskite microplate-based photodetectors. In particular, chlorine (Cl) can be efficiently incorporated into the micropla...

Herein, we investigate the effects of proton irradiation on the structure and shape recovery characteristics of a NiTi alloy and provide a mechanistic explanation of the observed phenomena. Detailed analysis revealed that bombardment with 3 MeV protons induced the formation of a complex multilayer structure comprising TiH2, Ti2Ni, austenite and austenite-martensite layers along the irradiation direction with increasing distance and the origin of the above structure was shown to be closely related to the preferential sputtering effect and irradiation-induced segregation. Finally, the shape recovery characteristics significantly deteriorated with increasing irradiation fluence, since the multilayer structure hindered the martensitic transformation.

The effect of Zr substituting for Ti in Ti50-xNi44Cu6Zrx alloys on the martensitic transformation behavior, microstructure, mechanical and shape memory properties was investigated systematically. The results showed that the Ti-Ni-Cu-Zr alloys were featured with the single step (B2⇋B19′) martensitic transformation. The transformation temperatures decreased linearly in approximate with the Zr content increasing up to 5 at.%. The Mp and Ap temperatures can be calculated by linear regression as: Mp (°C) = 51.565–11.733×; Ap (°C) = 69.695–10.408×, respectively. With further increasing of the Zr content, the transformation temperatures increased continuously in a linear relationship. The Mp and Ap temperatures can be expressed by linear regression as: Mp (°C) = 4.53x-33.38; Ap (°C) = 9.10x-24.12, separately. The Zr addition resulted in the reduction of the size of the Ti2Ni type second phase. Instead, a Zr-rich zone at the neighborhood of the Ti2Ni type second phase appeared owing to Zr addition. Based on the solution strengthening, the critical stress for the martensite reorientation and the tensile strength were significantly elevated, and further improving the shape memory effect. The complete recoverable strain of 4% and the largest tensile strain of 16.5% can be obtained in Ti-Ni-Cu-Zr alloy containing 3 at.% Zr.

Organic–inorganic metal halide perovskites have attracted great attention as optoelectronic materials because of their low cost, relative insensitivity to defects, and solution-processible properties. However, some of their properties, such as thermal instability, toxicity, and current–voltage hysteresis still remain elusive. Ion migration, which has been proven to be a thermal-activated process, is regarded as one of the major origins of the hysteresis and thus detrimental to the long-term stability of the optoelectronic devices. Nevertheless, by using the external electric field to pole the perovskite, ion migration would be possible to be utilized to create dynamic electronic junctions. In this paper, electric-field-induced dynamic electronic junctions have been manipulated for photodetection and energy harvesting through the ion migration under external electric field. Ion-migration-induced p–n or n–p junction has been successfully created via tuning the polarity of the external applied voltage, which is used for photodetection with a relatively fast response. By freezing out of the nonuniformly distributed ions after migration at low temperature, we demonstrate that the ion-migration-induced dynamic junctions can function as an energy harvesting device with an external quantum efficiency of 20%.

Two-dimensional (2D) Ruddlesden–Popper perovskites with high exciton binding energy and great environmental stability have recently attracted great attention for their promising potential optoelectronic applications. The controllable growth of 2D perovskites with desired shapes would be critical for improving the performance of 2D perovskite-based optoelectronic devices. However, the investigation on this is still in its infancy. Here, we report on the controllable synthesis of 2D (C4H9NH3)2PbI4 microstructures with a butterfly shape, (C4H9NH3)2(CH3NH3)Pb2I7 and (C4H9NH3)2PbI4/(C4H9NH3)2(CH3NH3)Pb2I7 microstructures with a square shape by a solution-processing method. We have systematically investigated the influence of the substrate, mass ratio and crystallization temperature on the morphology evolution of the as-synthesized 2D perovskite microstructures. Atomic force microscopy (AFM) and optical microscopy (OM) images show that the size and thickness of the resultant products are positively correlated with their mass ratio and negatively correlated with their crystallization temperature. X-ray diffraction (XRD) patterns, fluorescence imaging, temperature-dependent photoluminescence (PL) and absorption studies confirm the crystalline structures and optical properties of the as-synthesized regularly shaped 2D perovskite microstructures. Our studies provide a simple method to controllably synthesize 2D perovskite microstructures without using very toxic solvents and thus offer a platform to investigate the optical and charge transport properties of 2D perovskite materials for the further design of new device architectures with enhanced performance.

Polymer-assisted deposition (PAD) method has been employed to prepare SrTiO 3 (STO) films on ITO substrates, which have been applied as cathode buffer layer in inverted polymer solar cells. ZnO and TiO 2 films on ITO glass were also prepared via PAD and have been utilized as cathode buffer layers in the inverted polymer solar cells for comparison, which show better efficiency than those using ZnO and TiO 2 as interfacial layers prepared through other methods. The power conversion efficiency (PCE) of ∼3.5% was achieved with STO as the cathode buffer layer as well as MoO 3 as the anode buffer layer, which is comparable to that with ZnO and TiO 2 prepared using the same method as cathode buffer layers. Our findings indicate that STO has the potential to be a candidate as interfacial layers in solar cell devices.

The element distribution and surface microstructure in NiTi shape memory alloys exposed to 3 MeV proton irradiation were investigated. Redistribution of the alloying element and a clearly visible multilayer structure consisting of three layers were observed on the surface of NiTi shape memory alloys after proton irradiation. The outermost layer consists primarily of a columnar-like TiH2 phase with a tetragonal structure, and the internal layer is primarily comprised of a bcc austenite phase. In addition, the Ti2Ni phase, with an fcc structure, serves as the transition layer between the outermost and internal layer. The above-mentioned phenomenon is attributed to the preferential sputtering of high energy protons and segregation induced by irradiation.

Two-dimensional organic-inorganic perovskites have attracted considerable interest recently. Here, we present a systematic study of the temperature-dependent photoluminescence on phase pure (n-BA)2(MA) n-1Pb nI3 n+1 ( n = 1-5) and (iso-BA)2(MA) n-1Pb nI3 n+1 ( n = 1-3) microplates obtained by mechanical exfoliation. The photoluminescence peak position gradually changes from a red-shift for n = 1 to a blue-shift for n = 5 with an increase in temperature in the (n-BA)2(MA) n-1Pb nI3 n+1 ( n = 1-5) series, while only a monotonous blue-shift has been observed for the (iso-BA)2(MA) n-1Pb nI3 n+1 ( n = 1-3) series, which can be attributed to the competition between the thermal expansion interaction and electron-phonon interaction. In the (n-BA)2(MA) n-1Pb nI3 n+1 ( n = 1-5) series, the thermal expansion interaction and electron-phonon interaction are both gradually enhanced and the former progressively dominates the latter from n = 1 to n = 5, resulting in the band gap versus temperature changing from a red-shift to a blue-shift. In contrast, both of these factors show a weaker layer thickness dependence, leading to the monotonous blue-shift in the (iso-BA)2(MA) n-1Pb nI3 n+1 ( n = 1-3) series.

Chiral materials with intrinsic inversion-symmetric structures possess many unique physicochemical features, including circular dichroism, circularly polarized photoluminescence, nonlinear optics, ferroelectricity, and spintronics. Halide perovskites have attracted considerable attention owing to their excellent optical and electrical properties, which are particularly suitable for realizing high power-conversion efficiency in solar cells. Recent studies have shown that chirality can be transferred from chiral organic ligands into halide perovskites and the resultant chiral perovskites combine the advantages of both chiral materials and halide perovskites; this provides an ideal platform to design next-generation optoelectronic and spintronic devices. In this progress report, the most recent advances are summarized in various chemical structures of chiral perovskites, their synthesis strategies, chirality generation mechanisms, and physical properties. Furthermore, the potential chiral-halide-perovskite-based applications are presented and the challenges and prospects of chiral perovskites are discussed. This report outlines the diverse construction strategies of and proposes research directions for chiral halide perovskites; thus, it provides insights into the design of novel chiral perovskites and facilitates investigation of the optoelectronic applications that employ chirality.

To simulate the impact of space debris, Ti 50 Ni 50 alloy is impacted at 1.2 km s −1 using a powder gun. Phase transformation, microstructure and mechanical properties in Ti 50 Ni 50 alloy induced by impact are investigated. The results show that the phase transformation temperature shifts to a lower temperature in impacted Ti 50 Ni 50 alloy. Variants lose their self-accommodated morphology, martensite plates widen, the variants interfaces migrate and bend under force, and many dislocations exist in the martensite plates. The microhardness reduces and the shape recovery ratio enhances gradually with the increase in distance from the crate. This is attributed to plastic deformation and working hardening caused by high-velocity impact.

In the present work, the mechanical and strain recovery characteristics of Ti–V–Al–B shape memory alloy were tailored by changing annealing temperatures. Moreover, effect of annealing temperatures on microstructure and martensitic transformation behavior were investigated systematically. At the annealing temperatures of 650 °C and 700 °C, both α" martensite phase and hard α phase coexisted in the annealed Ti–V–Al–B alloys. With the annealing temperatures increasing, amount of α phase gradually decreased and α" martensite phase was dominated. The reduction of α phase resulted in the compositional variation, which further triggered the rising of transformation temperatures. The elongation of annealed Ti–V–Al–B alloys continuously increased with the annealing temperatures increasing; whereas the yield strength gradually decreased. The mechanical properties were closely related to the amount of α precipitates and dislocations. Under optimum annealing condition of 700 °C, the maximum yield strength of 489 MPa can be achieved in Ti–V–Al–B alloy. Meanwhile, it showed a largest recoverable strain of 4.6% in correspondence to 6% applied pre-strain.

In the present study, in-situ TiB phase and La2O3 phase with a three dimensional (3D) network structure were introduced into Ti–Ni composite via the lower energy ball milling and hot pressed sintering. The dimension of network structure and the amount of in-situ reinforcement forming network structure were determined by size of original alloy powder. Only one-stage martensitic transformation was observed in (TiB + La2O3)/Ti–Ni composite, regardless of network structure size. The martensitic transformation temperatures were slightly lower in (TiB + La2O3)/Ti–Ni composite with 100–150 μm network structure. The higher strength and superior strain recovery characteristics of in-situ (TiB + La2O3)/Ti–Ni composite can be obtained by adjusting the network structure. The maximum fracture stress and strain of 2474 MPa and 34.7%, as well as the largest completely recoverable strain of 7% can be obtained in (TiB + La2O3)/Ti–Ni composite with the network structure size of 100–150 μm.

Magnetocaloric materials have shown huge potential for magnetic refrigeration but fail meeting the application standard because of the low magnetic entropy change ΔSM. In this work, high-energy electron irradiation is used to enlarge the magnetization difference ΔM in the inverse martensitic transition for Ni–Co–Mn–In alloys, which is mainly attributed to the variations of the short-range atomic arrangement and electronic structure. As a result, the ΔSM can reach up to 62.17 J/(kgK) only with a small magnetic field of 3 T. Even compared with the ΔSM of other works measured under 5 T magnetic field, this value is much superior and can be further improved up to 136.16 J/(kgK) with increasing the magnetic field to 7 T. Such high ΔSM could improve the attractiveness of the material for the actual application.

In the present paper, the mechanical and functional properties of Ti–V–Al alloy were tailored by adjusting the boron (B) content. In addition, the effect of B content on the microstructure and martensitic transformation behaviors of Ti–V–Al alloys was also explored. The results indicated that the microstructure of Ti–V–Al alloys was sole α'' martensite phase, irrespective of the B content. B was completely soluble in Ti–V–Al alloy, as B content was not more than 0.01 at.%. Further increased B content not only promoted to the formation of TiB phase, but also resulted in the remarkable grain refinement. During heating process, the orthorhombic structure α'' martensite transformed into β phase with a body-centered cubic structure in one stage manner for all Ti–V–Al alloys containing different B contents. With the increased B content, the transformation temperature firstly decreased and then increased. Moderate B addition can improve significantly the mechanical properties and strain recovery characteristics of Ti–V–Al alloys owing to the perfect combination of solution strengthening, grain refinement, and precipitation strengthening of in-situ TiB phase. The maximum yield strength of 711 MPa can be obtained in 0.1 at.%B doped Ti–V–Al alloy with superior elongation of 18.5%. Moreover, it showed the largest recoverable strain of 5.1% under the condition of 6% pre-strain.

Effect of Gd addition on microstructure, martensitic transformation and strain recovery characteristics was investigated. Gd addition resulted in the significant reduction of grain size and formation of Gd-rich phase. The Gd-rich phase was identified as Gd3(Ti,V) phase with an orthorhombic structure. The solution treated (Ti-13V-3Al)100−xGdx alloys underwent a α″ → β transformation during heating, irrespective of Gd content. But Gd addition led to a slight drop of martensitic transformation temperatures. In addition, the moderate Gd addition can promote the achievement of outstanding mechanical and functional properties due to the combination of the grain refinement and precipitation strengthening of Gd-rich phase in grain interior. Ti-V-Al alloy with an optimal Gd content, which was Ti-V-Al alloy containing 0.3 at.% Gd, showed the largest recoverable strain of 4.9% at a pre-strain of 6% and the ultimate tensile stress of 925 MPa. Meanwhile, Ti-V-Al alloy had a superior elongation of 20.7%, as 0.3 at.% Gd was added.

In the present study, the effect of Co addition on the microstructural features, martensitic transformation beahviors and mechanical properties of Ti–V–Al alloys was investigated systematically. The results revealed that phase constituents varied with Co content increasing, which can be summarized as follows: sole α" martensite phase → coexistence of α" martensite phase and β austenite phase → fully β austenite phase. Correspondingly, the reverse martensitic transformation temperature continuously decreased with Co content increasing. Moreover, the moderate Co addition can improve yield strength and elongation of Ti–V–Al alloys as a consequence of the solid solution strengthening effect. The maximum yield stress of 811 MPa and superior elongation of 23.8% can be obtained in Ti–V–Al–Co2.0 and Ti–V–Al–Co1.0 alloy, respectively. Besides, Co addition led to the significant improvement of the higher temperature yield strength of quaternary Ti–V–Al–Co alloys, compared with the Ti–V–Al alloy without Co addition.

TiNi thin films have attracted wide attentions as actuator materials in the micro-electro-mechanical systems (MEMs) for aerospace craft. However, multiple irradiation, such as the proton, was generally considered as an essential expired factor for the materials used in the aerospace. The present paper focused on the microstructure, martensitic transformation and shape recovery property of TiNi thin films after being irradiated by proton. A single layer structure B19′ phase to a dual-phase (B2 and B19′) with multilayer structure after proton irradiation have been revealed through a combination technique of grazing incidence (GI) XRD and TEM. As-formed irradiated films with amorphous layer and B2 austenite phase displayed a two-step martensitic transformation behavior, which occurred in the irradiated and the unirradiated layer. In contrast, the unirradiated counterparts just exhibited a single-step martensitic transformation. In addition, some defects could be seen after the TiNi films being irradiated. Such defects could induce a stress field that produces the R phase in the B2 phase. Furthermore, the synergistic effect of preferential sputtering effect and inverse Kirkendall effect induced the GP zones in the irradiated layer after 120 keV proton irradiation. The existence of amorphous phase and precipitation significantly deteriorated the shape recovery property.

Two-dimensional (2D) hybrid organic-inorganic perovskites have recently attracted attention due to their layered nature, naturally formed quantum well structure, large exciton binding energy and especially better long-term environmental stability compared with their three-dimensional (3D) counterparts. In this report, we present a brief overview of the recent progress of the optoelectronic applications in 2D perovskites. The layer number dependent physical properties of 2D perovskites will first be introduced and then the different synthetic approaches to achieve 2D perovskites with different morphologies will be discussed. The optical, optoelectronic properties and self-trapped states in 2D perovskites will be described, which are indispensable for designing the new device structures with novel functionalities and improving the device performance. Subsequently, a brief summary of the advantages and the current research status of the 2D perovskite-based heterostructures will be illustrated. Finally, a perspective of 2D perovskite materials is given toward their material synthesis and novel device applications.

Despite the huge progress achieved over the past decade, the relationship between the molecular weights of dyes and the performance of dye-sensitized solar cells (DSSCs) remains unclear. In this article, we report on the fine control of the number-average molecular weight (Mn) of poly(triphenylamine-2,2′-bithiophene) (PPAT) dyes with cyanoacrylic acid moieties as acceptors. We found a correlation between the Mn and photovoltaic performance of these polymers when they were used for DSSC applications. In this study, three samples (PPAT-01, PPAT-02, and PPAT-03) with different Mn values (Mns = 1700, 2800, and 3500 g/mol) were prepared through the control of the polymerization time and characterized by analytical gel permeation chromatography and NMR. Under the same experimental conditions, the overall cell efficiency of the oligomer dyes showed a nonmonotonic tendency with increasing molecular weight. The power-conversion efficiencies were 2.81% for PPAT-01, 4.72% for PPAT-02, and 1.88% for PPAT-03. UV absorption measurements proved that PPAT-03 formed aggregation, whereas PPAT-01 and PPAT-02 were in the monolayer state adsorbed on TiO2. The larger aggregation decreased charge transfer; thus, poor photoelectric conversion performance was observed. Furthermore, a higher molecular weight reduced the amount of PPAT-03 adsorbed on TiO2, and this had a crucial effect on the performance of the cells because of the reduced photocurrent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44182.

The effects of a high-velocity impact on the microstructure, phase transformation and mechanical property of aged Ti49Ni51 alloy are investigated. The transformation behavior and microstructure along the impact direction after impact emerge with regionalization characteristics, including a deformed region near the crater (0–4 mm) and an un-deformed region of the distal crater (5–6 mm). Stress-induced martensite is the main deformation mechanism in the deforming region of aged Ti49Ni51 alloy under high-velocity impact.

The two-dimensional (2D) Ruddlesden–Popper type perovskites have attracted intensive interest for their great environmental stability and various potential optoelectronic applications. Fundamental understanding of the photophysical and electronic properties of the 2D perovskites with pure single phase is essential for improving the performance of the optoelectronic devices and designing devices with new architectures. Investigating the optical and electronic properties of these materials with pure single phase is required to obtain pure single phase 2D perovskites. Here, we report on an alternative approach to fabricate (C4H9NH3)2(CH3NH3) n−1Pb n I3n+1 microplates with pure single n-number perovskite phase for n > 2 by mechanical exfoliation. Micro-photoluminescence and absorption spectroscopy studies reveal that the as-synthesized 2D perovskite plates for n > 2 are comprised by dominant n-number phase and small inclusions of hybrid perovskite phases with different n values, which is supported by excitation power dependent photoluminescence. By mechanical exfoliation method, 2D perovskite microplates with the thickness of around 20 nm are obtained, which surprisingly have single n-number perovskite phase for n = 2–5. In addition, we have demonstrated that the exfoliated 2D perovskite microplates can be integrated with other 2D layered materials such as boron nitride, and are able to be transferred to prefabricated electrodes for photodetections. Our studies not only provide a strategy to prepare 2D perovskites with a single n-number perovskite phase allowing us to extract the basic optical and electronic parameters of pure phase perovskites, but also demonstrate the possibility to integrate the 2D perovskites with other 2D layered materials to extend the device's functionalities.