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The phase transformation from martensitic twins to austenite phase in NiTi shape memory alloys (SMAs) determines their shape memory effect (SME). However, systematic studies are indeed needed to reveal which martensitic twin type is effective in enhancing the SME for NiTi SMAs due to the diversity of martensitic twins. In this work, based on laser powder bed fusion (LPBF) NiTi SMAs, an excellent strength-ductility combination of 900.5 MPa and 13.9% was obtained by utilising a low laser power (70 W) and scanning speed (200 mm/s), which represents one of the highest values attainable among current LPBF NiTi SMAs. Furthermore, based on transmission kikuchi diffraction, it is found that high-density [Formula: see text] I-type martensitic twins enhanced the SME of LPBF NiTi SMAs significantly, and the maximum SME recovery ratio is 95.8% after 10 cycles at controlled strain (6%) cyclic tensile loading-unloading. Conversely, the formation of [Formula: see text] I-type martensitic twins in the matrix weakened the SME of LPBF NiTi SMAs remarkably and lost SME after 10 cycles at controlled strain (6%) cyclic tensile loading-unloading. This research offers some valuable insights into the relationship between martensitic twin and SME for LPBF NiTi SMAs and paves the new way for modulation of microstructure to enhance mechanical properties and SME for NiTi SMAs via LPBF.

Abstract Additively manufactured metallic materials typically exhibit preferential or crystallographic orientations along the build direction. Nowadays, the challenge is to program crystallographic orientation along arbitrary 3D direction in additive‐manufactured materials. In this work, it is established a technique of multitrack coupled directional solidification (MTCDS) to program the crystallographic orientation along an arbitrary 3D direction in biomedical beta‐type Ti‐Nb‐Zr‐Ta alloys via laser powder bed fusion (LPBF). MTCDS can be achieved via directional solidification of coupled multi‐track melt pools with a specific temperature gradient direction. This results in continuous epitaxial growth of the β‐Ti phase and consequently sets the crystallographic orientation along an arbitrary 3D direction. This way, relatively low elastic modulus values of approximately 60 ± 1.2 GPa are customized along an arbitrary 3D direction. It is expected that MTCDS can be generalized to a wide range of applications for programming specific crystallographic orientations and, respectively, tailoring desired properties of different metallic materials.

The morphology and distribution of silicides in α/α+β type titanium alloys impress on their properties. Nevertheless, the types of silicide precipitates and their formation mechanisms remain unclear in β-type Ti–Nb–Zr–Ta alloys. In this study, we report the precipitation behavior of silicides formed upon aging treatment of a laser powder bed fusion (LPBF)-fabricated β-type Ti–34.5Nb–6.9Zr–4.9Ta–1.4Si (wt%, TNZTS) alloy. We further discuss their underlying formation mechanism and silicide selection-oriented mechanical properties tailoring for LPBF-fabricated TNZTS alloy. Two novel silicide precipitates were formed: a supersaturated Si–rich β–Ti matrix in the form of a network that can further transform into the (Ti, Zr)2Si (S2) phase with the increase of aging temperature; and a short, rod-like S2 precipitate adjacent to pre-existing dot-shaped S2. The former results from the aggregation of Si solute atoms towards to the dislocation walls/microbands and the subsequent precipitation reaction, while the latter arises from the considerable micro-strain around the phase boundary between the dot-shaped S2 and β-Ti owing to the large difference in their thermal expansion coefficients. The aging-treated TNZTS alloy exhibits a good combination of tensile strength (1083 ​± ​5 ​MPa) and fracture strain (5.6% ​± ​1.0%), which is attributed to precipitation strengthening, grain-boundary strengthening, and discontinuous intergranular silicide derived from phase selection. The obtained results provide a basis for the design and fabrication of biomedical Si-containing β-type Ti alloys with excellent mechanical properties.

Defects are believed to always scatter carriers. Here, the authors find that the quantum gaps in GeTe-based materials do not scatter carriers, which decouple the carriers and phonons transport leading to high thermoelectric performance.

Experimentally detectable signature of an axion insulator remains elusive. Here, the authors predict a topological phase diagram of MnBi2Te4/(Bi2Te3)n heterostructure, where the chiral hinge mode induced by the surface anomalous Hall conductivity is identified as a signature of an axion insulator state.

Power conversion efficiency (PCE) of the perovskite solar cells (PSCs) has remarkably been increased from 3.1% to 25.2%. The fast expansion of the PSCs has been along with the development of compositional and interface engineering, which has been playing a critical role. For the PSCs with record high-efficiency and stability, the perovskite absorber layer has been changed from the initial MAPbI3- to FAPbI3-based compositions. Owing to the enormous engineering works, perovskite absorber layers with monolithic grains could be achieved, in which the interior defects are negligible compared with the surface defects. Therefore, interface engineering, which can passivate the surface defects and/or isolate the perovskite from the environmental moistures, has been playing a more and more important role to further boost the PCE and stability of the PSCs. Herein, a compact review study of the compositional and interface engineering is presented and promising strategies and directions of the PSCs are discussed.

Abstract Infra-red emission (980 nm) of sub 10 nm Yb3+-doped NaYF4 nanoparticles has been sensitized through the excitation of 2-hydroxyperfluoroanthraquinone chromophore (1,2,3,4,5,6,7-heptafluro-8-hydroxyanthracene-9,10-dione) functionalizing the nanoparticle surface. The sensitization is achieved with a broad range of visible light excitation (400–600 nm). The overall near infra-red (NIR) emission intensity of Yb3+ ions is increased by a factor 300 as a result of the broad and strong absorption of the chromophore compared with ytterbium’s intrinsic absorption. Besides the Yb3+ NIR emission, the hybrid composite shows organic chromophore-based visible emission in the orange-red region of the spectrum. We observe the energy migration process from the sensitized Yb3+ ions at the surface to those in the core of the particle using time-resolved optical spectroscopy. This highlights that the local environments for emitting Yb3+ ions at the surface and center of the nanoparticle are not identical, which causes important differences in the NIR emission dynamics. Based on the understanding of these processes, we suggest a simple strategy to control and modulate the decay time of the functionalized Yb3+-doped nanoparticles over a relatively large range by changing physical or chemical parameters in this model system.

The steady-state spectra and fluorescence lifetimes are investigated under vacuum for methylammonium lead bromide and iodide (CH3NH3PbBr3 or MAPbBr3, and CH3NH3PbI3 or MAPbI3) thin films by stably controlling the sample temperature in the range of 78 K to 320 K. The transformation of spectrum features and lifetime components are proved to be quite sensitive to the temperatures in accordance with the phase transition of structures. Our work demonstrates that the halide anions I- and Br- lead to remarkable differences on optical characteristics. Due to the distinct behaviors of excitons, electron-hole pairs and free carriers in decay channels, MAPbI3 has much longer lifetime and higher low-temperature fluorescence efficiency than those of MAPbBr3. The findings provide possible choices for certain perovskites under various ambient temperature conditions to display photovoltaic or luminescent advantage.

Abstract Copy number variation (CNV) is a genetic structural polymorphism important for phenotypic diversity and important economic traits of livestock breeds, and it plays an important role in the desired genetic variation. This study used whole genome sequencing to detect the CNV variation in the genome of 6 local Tibetan sheep groups. We detected 69,166 CNV events and 7230 copy number variable regions (CNVRs) after merging the overlapping CNVs, accounting for 2.72% of the reference genome. The CNVR length detected ranged from 1.1 to 1693.5 Kb, with a total length of 118.69 Mb and an average length of 16.42 Kb per CNVR. Functional GO cluster analysis showed that the CNVR genes were mainly involved in sensory perception systems, response to stimulus, and signal transduction. Through CNVR-based Vst analysis, we found that the CACNA2D3 and CTBP1 genes related to hypoxia adaptation, the HTR1A gene related to coat color, and the TRNAS-GGA and PIK3C3 genes related to body weight were all strongly selected. The findings of our study will contribute novel insights into the genetic structural variation underlying hypoxia adaptation and economically important traits in Tibetan sheep.

The photoluminescence (PL) variations of organic-inorganic hybrid lead halide perovskites in different atmospheres are well documented, while the fundamental mechanism still lacks comprehensive understandings. This study reports the reversible optical and electrical properties of methylammonium lead bromide (MAPbBr3 or CH3NH3PbBr3) single crystals caused by air infiltration. With the change in the surrounding atmosphere from air to vacuum, the PL intensity of perovskite single crystals decreases, while the conductivity increases. By means of first-principles computational studies, the shallow trap states are considered as key elements in PL and conductivity changes. These results have important implications for the characterization and application of organic-inorganic hybrid lead halide perovskites in vacuum. [ABSTRACT FROM AUTHOR]

We have used the introduction of shallow hole traps in poly(3-hexyl-thiophene) to test one of the predictions of the bipolaron theory of magnetoconductance (MC). The results show that the introduction of shallow traps effectively increases the degree of energetic disorder in the transport states whilst not affecting the position of the Fermi level and that this results in an increase in the MC response. These results are demonstrated to be in qualitative agreement with the theory and suggest one mechanism through which trap states may affect the MC response of organic semiconductors. This work presents a controllable way of chemical doping to engineer a change in absolute current at a given bias depending on the choice of anodes. It also allows for tuning the magnitude of negative MC response and electroluminescence efficiency under different driving conditions. [ABSTRACT FROM AUTHOR]

We report thickness-tuned electrical transport in highly anisotropic three-dimensional Dirac semimetal ZrTe5 nanosheets with thickness down to 10 nm. We find that the resistivity peak temperature T* can be significantly tuned by the nanosheet thickness. When the thickness is reduced from 160 to 40 nm, T* reduces systematically from 145 to 100 K. However, with the thickness further reducing to 10 nm, T* shifts up to a higher temperature. From our analysis, the system transitions from a topological semimetal with two types of carriers to a single band with conventional hole carriers when the thickness is less than 40 nm. Furthermore, by tracking the thickness dependence of the carrier density, we find that the Fermi level shifts continuously downward from the conduction band to the valence band with decreasing the thickness. Our experiment reveals a thickness-tuned transition of band topology in ZrTe5 nanosheets which may be helpful for the understanding of the contrast observations in this material. [ABSTRACT FROM AUTHOR]