Crystals

To obtain a high-quality Al/steel dissimilar joint, a micro-groove-assisted vortex-friction stir lap welding (MG-VFSLW) process was developed. Through prefabricating micro-grooves on the steel plate surface by laser ablation, high-quality mechanical interlock and metallurgical bonding were obtained simultaneously in the MG-VFSLW process. The weld formation, interface microstructure, mechanical properties, and failure mode in MG-VFSLW were studied by comparing them with those in VFSLW. The results showed that a line load of the AA5083/SUS304 dissimilar joint up to 485.9 N/mm was obtained by MG-VFSLW, which is 40.1% higher than that in VFSLW. Remarkable intermetallic compound layers and cracks were found in VFSLW. The cracks were closely related to the oxides on the interface. However, in MG-VFSLW, cross-riveting aluminum rivets and steel rivets were formed on the interface due to the micro-grooves and flashes made by the laser ablation. Good metallurgical bonding was also formed between AA5083 and SUS304. No remarkable intermetallic compound layers and cracks occurred. During the tensile shear tests, the aluminum rivets were cut off and some dimples and tear ridges existed on the fracture surface. In short, the high strength of the Al/steel lap joint in MG-VFSLW was attributed to the high-quality mechanical interlock and metallurgical bonding. Full article

In the present work, hot working was used as a post-processing method for Fe-25Al-1.5Ta (at.%) alloy built using laser powder bed fusion (LPBF) to refine the undesirable columnar microstructure with heterogeneous grain sizes and strong textures in the build direction. The hot deformation behavior and workability were investigated using constitutive modeling and the concept of processing maps. Uniaxial compression tests were conducted up to a true strain of 0.8 at 900 °C, 1000 °C, and 1100 °C with strain rates of 0.0013 s⁻¹, 0.01 s⁻¹, and 0.1 s⁻¹. The constitutive equations were derived to describe the flow stress–strain behavior in relation to the Zener–Hollomon parameter. Processing maps based on a dynamic materials model were plotted to evaluate the hot workability and to determine the optimal processing window as well as the active deformation mechanisms. The microstructure of the deformed specimens was characterized by scanning electron microscopy equipped with an electron backscatter diffraction detector. The results indicated a high degree of hot workability of the LPBF builds without flow instabilities over the entire deformation range tested. The epitaxially elongated grains of the as-built alloys were significantly refined after deformation through dynamic softening processes, and the porosity was reduced due to compressive deformation. The current study revealed a well-suited parameter range of 1000–1080 °C/0.004–0.012 s⁻¹ for the safe and efficient deformation of the LPBF-fabricated Fe-25Al-1.5Ta alloys. The effectiveness of the process combination of LPBF with subsequent hot forming could be verified with regard to microstructure refinement and porosity reduction. Full article

Organic–inorganic composite scintillators, demonstrating advantages of easy large-area preparation and a high detection efficiency, have shown enormous potential application prospects in radiation detection and imaging. In this study, bulk polystyrene (PS) composite scintillators were successfully prepared by embedding inorganic BaF₂ particles with a loading amount of up to 80 wt% during the polymerization process of the plastic scintillator. The inorganic BaF₂ particles were uniformly dispersed in the organic matrix. With the increase of the loading amounts of BaF₂ particles, the X-ray-excited luminescence intensity of the PS-BaF₂ composite scintillators was about eight times higher than that of the commercial pure plastic scintillator. The scintillation counts under the gamma ray (59.5 KeV) irradiation also showed that the detection efficiency was obviously enhanced by BaF₂ particle loading. More importantly, their scintillation pulse retains the decay kinetics of the organic matrix without loading the slow-decay component of BaF₂. This work provides a promising solution for the application of the PS-BaF₂ composite scintillator in high-efficiency radiation detection and large-area imaging. Full article

A retro-Claisen reaction of 1-(4-oxo-4H-pyrido [1,2-a]pyrimidin-3-yl)butane-1,3-dione, 3, in the presence of potassium hydroxide and 4-dimethylamino-pyridine has been carried out, leading to 4-(dimethylamino)pyridin-1-ium 2-methyl-4-oxo-pyrido [1,2-a]pyrimidine-3-carboxylate 5. A plausible mechanism explaining the formation of the title compound has been proposed. A single-crystal X-ray diffraction analysis confirms the crystal structure of the isolated organic salt (5). In the crystal, the title compound adopts a layered structure where there are stacks of cations and anions formed by slipped π-stacking interactions. These stacks are linked by regions consisting of water molecules that are hydrogen-bonded together. DFT and Hirshfeld surface analysis supported the experimental results of the molecular geometry and the intercontacts between different units in the crystal. The druglikeness, ADMET properties, and predicted targets were investigated, and the observed results suggest that 5 may act as a carbonic anhydrase I inhibitor. The assumption is confirmed by docking 5 into the active binding site of carbonic anhydrase, which shows it to have good binding affinities and to form stable complexes with the active residues of carbonic anhydrase I. Full article

The high-temperature crystal growth of intermetallics often asks for sealing of the materials in a protective atmosphere. Here, we report on the development of a convenient sealing method for alkali-containing melts, with high vapor pressure and reactivity. Our newly designed container made of high-temperature resistant steel can be sealed manually and reliably without any air exposure of the containing material. The closed container may be heated in air up to at least 1150 ${}^{°}$C. The containers were applied for the development and optimization of a high-temperature self-flux growth of KFe${}_{1-x}$Ag${}_{1+y}$Ch${}_2$ (Ch = Se, Te) single crystals. Their crystal structure and the low-temperature electrical resistance are presented. The successful growths of these air-sensitive materials out of a reactive self-flux confirm the reliability of the container. Full article

We successfully synthesized millimeter-sized single crystals of the molecular erbium(III) complex Er(acac)₃(cphen), where acac = acetylacetonate and cphen = 5-chloro-1,10-phenanthroline. The novelty of this work stems from the exhaustive examination of the polar and electronic properties of the obtained samples at the macro-, micro-, and nanoscale levels. The single crystal X-ray diffraction method demonstrates the monoclinic (noncentrosymmetric space group P2₁) crystallographic structure of the synthesized samples and scanning electron microscopy exhibits the terrace–ledge morphology of the surface in erbium(III) crystals. By using the piezoelectric force microscopy mode, the origin of the polar properties and the hyperpolarizability in the synthesized samples were assigned to the internal domain structure framed by the characteristic terrace–ledge topography. The direct piezoelectric coefficient (~d33) was found to be intensely dependent on the local area and was measured in the range of 4–8 pm/V. A nanoscale study using the kelvin probe force and capacitance force (dC/dz) microscopy modes exposed the effect of the Er ions clustering in the erbium(III) complex. The PFM method applied solely to the Er ion revealed the corresponding direct piezoelectric coefficient (~d33) of about 4 pm/V. Given the maximum piezoelectric coefficient in the erbium(III) complex at 8 pm/V, we highlight the significant importance of the spatial coordination between the lanthanide ion and the ligands. The polar coordination between the lanthanide ion and the nitrogen and oxygen atoms was also corroborated by Raman spectroscopy supported by the density functional theory calculations. The obtained results can be of paramount importance for the application of molecular erbium(III) complex crystals in low-magnitude magnetic or electric field devices, which would reduce the energy consumption and speed up the processing switching in nonvolatile memory devices. Full article

Beryllium finds widespread applications in nuclear energy, where it is required to service under extreme conditions, including high-dose and high-dose rate radiation with constant bombardments of energetic particles leading to various kinds of defects. Though it is generally known that defects give rise to mechanical degradation, the quantitative relationship between the microstructure and the corresponding mechanical properties remains elusive. Here we have investigated the mechanical properties of imperfect hexagonal close-packed (HCP) beryllium via means of molecular dynamics simulations. We have examined the beryllium crystals with void, a common defect under in-service conditions. We have assessed three types of potentials, including MEAM, Finnis–Sinclair, and Tersoff. The volumetric change with pressure based on MEAM and Tersoff and the volumetric change with temperature based on MEAM are consistent with the experiment. Through cross-comparison on the results from performing hydrostatic compression, heating, and uniaxial tension, the MEAM type potential is found to deliver the most reasonable predictions on the targeted properties. Our atomistic insights might be helpful in atomistic modeling and materials design of beryllium for nuclear energy. Full article

Metal materials are vulnerable to corrosion in the process of production and service, which often leads to serious disasters, including the decline of the performance of metal components and the shortened service life, and even causes catastrophic accidents and ecological damage. Adding a certain amount of corrosion inhibitors (CIs) to the corrosive medium is a simple, efficient, and economical anti-corrosion method to slow down and restrain the corrosion of metal materials. Organic corrosion inhibitors (OCIs) are considered to have good application prospects and are widely used for surface anti-corrosion of metal materials, as they generally have advantages such as good metal adsorption, low oxidation resistance, good thermal and chemical stability, and green environmental protection. This paper systematically summarized some major OCIs, including alkyl chains, imidazoles, and pyridines, and their structural characteristics, as well as the action mechanism of OCIs. Moreover, this paper discusses some natural compounds used as environmentally friendly CIs and provides a prospect for the development trend of OCIs. Full article

Nanoparticles have a negative effect on the preparation of Gallium Nitride (GaN) by Metal-Organic Chemical Vapor Deposition (MOCVD). We developed a particle tracking and particle-wall collision model coupled with the bulk gas flow solver to investigate the motion and deposition of nanoparticles in single-wafer and multi-wafer reactors. The results indicated that for the single-wafer reactor, there is no particle deposition on the reactor wall and susceptor, but there is the endless movement of some particles within the reactor, which should be avoided. For the multi-wafer reactors, some of the nanoparticles are deposited near the axis, and those whose initial position is beyond a certain position from the axis are trapped in a vortex above the receptor, resulting in more complex by-products, although no particles are trapped in endless motion. Moreover, the effects of the rotational speed of the susceptor on the deposition rate for both the single-wafer reactor and the multi-wafer reactor were also simulated and analyzed. Full article

Titanium alloys additively manufactured by electron beam melting (EBM) inevitably obtained some pore defects, which significantly reduced the very high cycle fatigue performance. An ultrasonic fatigue test was carried out on an EBM TC21 titanium alloy with hot isostatic pressing (HIP) and non-HIP treatment, and the effect of pore defects on the very high cycle fatigue (VHCF) behavior were investigated for the EBM TC21 titanium alloy. The results showed that the S-N curve of non-HIP specimens clearly had a tendency to decrease in very high cycle regimes, and HIP treatment significantly improved fatigue properties. Fatigue limits increased from 250 MPa for non-HIP specimens to 430 MPa for HIP ones. Very high cycle fatigue crack mainly initiated from the internal pore for EBM specimens, and a fine granular area (FGA) was observed at the crack initiation site in a very high cycle regime for both non-HIP and HIP specimens. ΔK_FGA had a constant trend in the range from 2.7 $\mathrm{MPa}\sqrt{\mathrm{m}}$ to 3.5 $\mathrm{MPa}\sqrt{\mathrm{m}}$, corresponding to the threshold stress intensity factor range for stable crack propagation. The effect of pore defects on the very high cycle fatigue limit was investigated based on the Murakami model. Furthermore, a fatigue indicator parameter (FIP) model based on pore defects was established to predict fatigue life for non-HIP and HIP specimens, which agreed with the experimental data. Full article

Glucosamine hydrochloride (GAH) is a kind of natural hexose, which is used to promote the synthesis of mucopolysaccharides and improve the metabolism of articular cartilage. In this paper, the solubility of GAH in pure water and aqueous system with the presence of three kinds of additives (HCl, NaCl, KCl) at temperatures ranging from 278.15 K to 323.15 K was determined by gravimetric method. When there are additives in water, the solubility of GAH increases with the increase of temperature and decreases with the increase of concentration of the three kinds of additives. When the additives were at similar mole fractions, HCl led to the lowest solubility of GAH. The modified Apelblat model and van’t Hoff model were used to correlate the solubility data. The average relative deviation (ARD) data of Apelblat and van’t Hoff models were less than 5%, indicating good fitting results. Based on the thermodynamic data, the cooling crystallization process of GAH was performed. It was found that the additives could affect the crystal morphology, particle size, and yield of GAH products. This study supplemented the thermodynamic data of GAH and studied the cooling crystallization process in the presence of GAH additives, which provided important guidance for the optimization of the crystallization process. Full article

Strain engineering is an effective way to adjust the sensing properties of two-dimensional materials. In this paper, lateral heterojunctions (LHSs) based on arsenic and antimony have been designed along the armchair (AC) or zigzag (ZZ) edges. The adsorption and sensing characteristics of As/Sb LHSs to NO₂ before and after applying different types of strain are calculated by first principles. The band gaps of all As/Sb heterostructures are contributed by As-p and Sb-p orbitals. In addition, the adsorption energy of As/Sb ZZ-LHS with −4% compression strain is the largest. Furthermore, its work function changes significantly before and after the adsorption of NO₂. Meanwhile, strong orbital hybridizations near the Fermi level are observed and a new state is yielded after applying compressive strain. These results indicate that the As/Sb LHS with ZZ interface under −4% compression strain possesses the best sensing properties to NO₂. This work lays the foundation for the fabrication of high-performance NO₂ gas sensors. High-performance gas sensors can be used to track and regulate NO₂ exposure and emission, as well as to track NO₂ concentrations in the atmosphere and support the assessment of air quality. Full article

In this work, to systematically investigate the evolution characteristics of electrical properties in polymorphic piezoceramics, the Ba(Ti_0.92Zr_0.08)O₃ ceramics are selected as a paradigm that possesses all the general phase structures above room temperature. It is found that the evolution of electrical properties with temperature change can be divided into three stages based on phase structure transforming: high ferroelectric and stable strain properties at R and R-O, high ferroelectric and enhanced strain/converse piezoelectric properties at O, O-T, and T phase, and the rapidly decreased ferroelectric and strain properties in T-C and C phase. However, the ferroelectric and strain properties all increase with rising electric field and their evolution can be divided into two parts based on phase structures. The high property and slow increase rate are present at R, R-O, O, and O-T, while the poor property but a high increase rate is present around T-C. Similar results can be found in the evolution of electrostrictive property. Finally, the highest d₃₃* of ~1240 pm/V and Q₃₃ of ~0.053 m⁴/C² are obtained at O-T due to the high ferroelectricity but easy domain switching. This work affords important guidance for the property optimization of polymorphic piezoceramics. Full article

A novel approach for manufacturing porous materials, foreseen as solar receivers for concentrated sun radiation, used in the power tower technology is presented. In such applications, materials are subjected to steep thermal gradients and thousands of cycles. Yet, materials consisting of honeycombs and ceramic foams showed insufficient thermal performance. By using the fused filament fabrication process, one can design printed parts meeting the requirements for solar receivers, namely dark color and high solar absorptance. This exploratory study unveils data on the retained crushing strength of newly developed 3D-printed porous Black Zirconia cubes after thermal cycling under similar conditions to those experienced by volumetric receivers and catalyst substrates for solar fuels (H₂ and/or CO) production via the thermochemical cycle. Unlike dense ceramics, the resistance to thermal shock of 3D-printed cubes underwent a gradual decrease with the increase in the thermal gradient. The thermal shock cycles were performed between 800 °C and 1100, 1200, and 1300 °C, corresponding to a ΔT of 300, 400, and 500 K, respectively. Additionally, water quenching tests were performed at ΔT = 300 K up to 400 K. Crushing strength measurements carried out to evaluate the retained mechanical strength after exposure up to 100 cycles showed that the Black Zirconia cubes can withstand thermal gradients up to at least 400 K. Full article

The recently discovered Cu₄₆Zr_33.5Hf_13.5Al₇ (at.%) bulk metallic glass (BMG) presents the highest glass-forming ability (GFA) among all known copper-based alloys, with a record-breaking critical casting thickness (or diameter) of 28.5 mm. At present, much remains to be explored about this new BMG that holds exceptional promise for engineering applications. Here, we report our study on the crystallization behavior of this new BMG, using isochronal and isothermal differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). With the calorimetric data, we determine the apparent activation energy of crystallization, the Avrami exponent, and the lower branch of the isothermal time–temperature–transformation (TTT) diagram. With XRD and TEM, we identify primary and secondary crystal phases utilizing samples crystallized to different degrees within the calorimeter. We also estimate the number density, nucleation rate, and growth rate of the primary crystals through TEM image analysis. Our results reveal that the crystallization in this BMG has a high activation energy of ≈360 kJ/mole and that the primary crystallization of this BMG produces a high number density (≈10²¹ m⁻³ at 475 °C) of slowly growing (growth rate < 0.5 nm/s at 475 °C) Cu₁₀(Zr,Hf)₇ nanocrystals dispersed in the glassy matrix, while the second crystallization event further produces a new phase, Cu(Zr,Hf)₂. The results help us to understand the GFA and thermal stability of this new BMG and provide important guidance for its future engineering applications, including its usage as a precursor to glass–crystal composite or bulk nanocrystalline structures. Full article

Environmentally friendly lead-free K_1-xNa_xNbO₃ (KNN) ceramics possess electromechanical properties comparable to lead-based ferroelectric materials but cannot meet the needs of device miniaturization, and the corresponding thin films lack theoretical and experimental studies. To this end, we developed the nonlinear phenomenological theory for ferroelectric materials to study the effects of non-equiaxed misfit strain on the phase structure, electromechanical properties, and electrical response of K_0.5Na_0.5NbO₃ epitaxial films. We constructed in-plane misfit strain ($u_1-u_2$) phase diagrams. The results show that K_0.5Na_0.5NbO₃ epitaxial film under non-equiaxed in-plane strain can exhibit abundant phase structures, including orthorhombic $a_{1}c$, $a_{2}c$, and $a_1{a}_2$ phases, tetragonal $a_1$, $a_2$, and $c$ phases, and monoclinic $r_{12}$ phases. Moreover, in the vicinity of $a_{2}c-r_{12}$, $a_{1}c-c$, and $a_1{a}_2-a_2$ phase boundaries, K_0.5Na_0.5NbO₃ epitaxial films exhibit excellent dielectric constant ${\epsilon }_{11}$, while at $a_{2}c-r_{12}$ and $a_{1}c-c$ phase boundaries, a significant piezoelectric coefficient $d_{15}$ is observed. It was also found that high permittivity ${\epsilon }_{33}$ and piezoelectric coefficients $d_{33}$ exist near the $a_{2}c-a_2$, $a_1{a}_2-r_{12}$, and $a_{1}c-a_1$ phase boundaries due to the existence of polymorphic phase boundary (PPB) in the KNN system, which makes it easy to polarize near the phase boundaries, and the polarizability changes suddenly, leading to electromechanical enhancement. In addition, the results show that the K_0.5Na_0.5NbO₃ thin films possess a large electrocaloric response at the phase boundary at the $a_1{a}_2-r_{12}$ and $a_{1}c-a_1$ phase boundaries. The maximum adiabatic temperature change $\mathsf{\Delta }T$ is about 3.62 K when the electric field change is 30 MV/m at room temperature, which is significantly enhanced compared with equiaxed strain. This study provides theoretical guidance for obtaining K_1−xNa_xNbO₃ epitaxial thin films with excellent properties. Full article

Aerospace structural components are in a complex stress state when they undertake load due to their specific geometric construction. Their fatigue behavior is quite different from the materials that undertake the standard stress state. The research on fatigue behavior of aircraft structures was the foundation of their design and life prediction. Lugs are one of the important connected components of aircrafts. In this paper, the mathematical mechanics’ method was used to calculate the structural feature parameters of TC18 Titanium alloy lugs under several specific loads. The design reference values of structural feature parameters were put forward for lugs. The fatigue behavior and fatigue failure characteristics under specific loads were studied experimentally. The fatigue experiment was conducted to verify the criterion, and the validity of the criterion mentioned above was confirmed by the test results. The fatigue life S-N curves under different loading forms and different mean stresses were researched. The fatigue failure characteristics, such as fatigue crack initiation, propagation, and final fracture, were also studied. These studies provided theoretical support for the anti-fatigue damage design of lugs. Full article

Hexagonal BN (h-BN) has emerged as an important ultrawide bandgap (UWBG) semiconductor (E_g~6 eV). The crystal growth technologies for producing semi-bulk crystals/epilayers in large wafer sizes and understanding of defect properties lag decades behind conventional III-nitride wide bandgap (WBG) semiconductors. Here we report probing of boron vacancy (V_B)-related defects in freestanding h-BN semi-bulk wafers synthesized by hydride vapor phase epitaxy (HVPE). A photocurrent excitation spectroscopy (PES) was designed to monitor the transport of photoexcited holes from deep-level acceptors. A dominant transition line at 1.66 eV with a side band near 1.62 eV has been directly observed, which matches well with the calculated energy levels of 1.65 for the V_B-H deep acceptor in h-BN. The identification of V_B complexes via PES measurement was further corroborated by the temperature-dependent dark resistivity and secondary ion mass spectrometry measurements. The results presented here suggested that it is necessary to focus on the optimization of V/III ratio during HVPE growth to minimize the generation of V_B-related defects and to improve the overall material quality of h-BN semi-bulk crystals. The work also provided a better understanding of how V_B complexes behave and affect the electronic and optical properties of h-BN. Full article

Protein adsorption is essential for determining material biocompatibility and promoting adherent cell growth. In this study, we focused on the a-plane structure of hydroxyapatite (HAp). This a-plane structure closely resembles the crystal plane where apatite is exposed in long bones. We conducted protein adsorption experiments using HAp ceramics with a preferred orientation to a-planes (aHAp), employing bovine serum albumin (BSA), lysozyme, and fetal bovine serum (FBS) as protein models to mimic the in vivo environment. Higher zeta potential and contact angle values were found in aHAp than in HAp ceramics fabricated from commercial HAp powder (iHAp). Bradford-quantified protein adsorption revealed BSA adsorption of 212 ng·mm⁻² in aHAp and 28.4 ng mm⁻² in iHAp. Furthermore, the Bradford-quantified protein adsorption values for FBS were 2.07 μg mm⁻² in aHAp and 1.28 µg mm⁻² in iHAp. Two-dimensional electrophoresis (2D-PAGE) showed a higher number of protein-derived major spots in aHAp (37 spots) than in iHAp (12 spots). Mass spectrometry analysis of the resulting 2D-PAGE gels revealed proteins adsorbed on aHAp, including secreted frizzled-related protein 3 and vitamin K epoxide reductase complex 1, which are involved in cellular bone differentiation. Overall, these proteins are expected to promote bone differentiation, representing a characteristic property of aHAp. Full article