Single Crystal Research Articles

Investigation on high temperature fatigue-oxidation behavior of Ni-based single crystal with film cooling holes considering arrangement effect

The fatigue-oxidation behavior of Ni-based single crystal with film cooling holes (FCHs) fabricated by femtosecond laser was investigated considering arrangement effect. Low cycle fatigue tests were conducted under 900 °C/713 MPa and 1000 °C/500 MPa. The experimental results show that fatigue lifetime reduced as the temperature increased at equal proportional stress. And, the specimens with square penetration pattern have an average fatigue life that is higher than the specimens with triangle penetration pattern at the same condition. Then, the crack propagation modes are characterized on the fracture path, and the fatigue failure mechanism is revealed by analyzing the fracture morphology. The microstructure evolution around the FCHs shows that the fatigue crack nucleation is caused by the coupling effect of fatigue and oxidation. According to the damage mechanism, a new fatigue-oxidation coupling damage model is proposed based on crystal plastic theory. The calculation results using crystal plasticity finite element method (CPFEM) considering coupling damage show that the maximum resolved shear stress (RSS) of the FCHs triangular arrangement is higher than that of quadrilateral arrangement at the same condition. Finally, fatigue life is predicted based on coupling damage accumulation, and the results show that the accuracy of life prediction is within 2 times data dispersion band.

Three-dimensional reconstruction of porous CeO2 single crystal for effective electrolysis of carbon dioxide

In the quest for long-lasting energy alternatives, solid oxide electrolysers have become a crucial technology in facilitating the transformation of CO2 toward fuels and valuable chemicals. This study proposes a unique method for the catalytic reduction of carbon dioxide at the cathode using porous CeO2 single-crystal electrodes in a solid oxide electrolyser, utilizing temperatures from an industrial waste heat stream. The fluxes and chemical states of oxygen-containing species evolved from the cathode were identified and designed, and the catalytic process of CO2 reduction to CO was effectively regulated by the oxygen-containing species (lattice oxygen, oxygen vacancies and adsorbed oxygen). The results show that the CO yield can reach 6.05 mL min−1 cm−1 with porous (111) CeO2 single crystal as the cathode at 850 °C and 1.8 V. The solid oxide electrolyser exhibits remarkable stability even after 100 h of continuous operation.

Effect of vacuum diffusion bonding on the mechanical and conductive properties of bonded bulk copper single crystals

Recrystallization-free atomic-level (AL) bonding between bulk copper single crystals was achieved by combining chemical mechanical polishing (CMP) and vacuum diffusion bonding. Under various bonding conditions, the bonded copper specimens can be classified into three categories: AL-bonded, HH-bonded, and L-bonded specimens. AL-bonded copper single crystals were obtained by performing bonding under 20 MPa at 600 °C for 60 min, achieving the mechanical and electrical properties that are closest to those of the parent copper single crystal. The AL-bonded interface is characterized by an asymmetrically tilted sub-grain boundary with a 2° misorientation and consists of two sets of edge dislocations with mutually perpendicular Burgers vectors. The formation of the AL-bonded interface depends on two critical factors: the creation of ultra-flat bonded surfaces and performing diffusion bonding within the elastic deformation range. Achieving an ultra-flat surface that eliminates residual stress allows for bonding under relatively low pressure. With a moderate bonding temperature and holding time, it is possible to simultaneously avoid the formation of voids and recrystallizations at the bonding interface, thereby achieving a high-quality AL-bonded interface between bulk copper single crystals.

Straight sections of step edges on a NiAl(110) curved single crystal surface used to calculate an approximation of step formation energy

Curved crystals may feature a smooth transition between different vicinal surfaces. Using one curved single crystal to study different vicinal surfaces requires less experimental time than using several single flat crystals. Here, we study step distributions on the (110) plane of a curved NiAl single-crystal surface, which consists of alternating Ni and Al atom rows. We use scanning tunneling microscopy under UHV conditions at room temperature and our home-built Python-based analysis script to obtain statistical information on kink and straight sections along step-edge distributions from STM images. We perform this analysis mainly to study this single crystal’s kink distributions and step termination We propose a new method to estimate the step formation energy based on step edge analysis and statistical mechanics. With this method, we find an approximation of the step formation energy for NiAl(110).

Influence of the number of particle variants on the cyclic stability of superelasticity in Ti-51.5at.%Ni single crystals

The influence of the crystallographic variants of Ti3Ni4 particles on the cyclic stability of the high-temperature superelasticity of 〈001〉 -oriented Ti-51.5at.%Ni single crystals after stress-free and stress-assisted aging at 823 K for 1 h was investigated for the first time. After stress-assisted aging, the single crystals exhibited low cyclic stability of superelasticity (irreversible strain was 5.2 %, and critical stresses decreased by 14 %). After cycling, single dislocations and {115}B2 twins were observed, as a consequence of B2-B19′-B2 martensitic transformations. After stress-free aging, single crystals showed high cyclic stability: critical stresses were practically unchanged, and the irreversible strain did not exceed 0.2 %. No defects were found after cyclic testing; the stress-free aged crystals had the high strength properties of the B2-phase (2100 MPa) and B19′-martensite (>2700 MPa), in contrast to the stress-assisted aged single crystals, which had the strength properties of the B2-phase, 1630 MPa, and B19′-martensite, 1650 MPa.

Atomic-Scale Insights into the High-Pressure Superconductor La3Ni2O7 and Topotactically Reduced LaNiO2 Single Crystals

Atomic-Scale Insights into the High-Pressure Superconductor La3Ni2O7 and Topotactically Reduced LaNiO2 Single Crystals

FePd2Te2: An Anisotropic Two-Dimensional Ferromagnet with One-Dimensional Fe Chains.

Two-dimensional (2D) magnets have attracted significant attention in recent years due to their importance in the research on both fundamental physics and spintronic applications. Here, we report the discovery of a new ternary compound FePd2Te2. It features a layered quasi-2D crystal structure with 1D Fe zigzag chains extending along the b-axis in the cleavage plane. Single crystals of FePd2Te2 with centimeter size could be grown. Density functional theory calculations, mechanical exfoliation, and atomic force microscopy on these crystals reveal that they are 2D materials that can be thinned down to ∼5 nm. Magnetic characterization shows that FePd2Te2 is an easy-plane ferromagnet with TC ∼ 183 K and strong in-plane uniaxial magnetic anisotropy. Magnetoresistance and the anomalous Hall effect demonstrate that ferromagnetism could be maintained in FePd2Te2 flakes with large coercivity. A crystal twinning effect is observed by scanning tunneling microscopy which makes the Fe chains right angle bent in the cleavage plane and creates an intriguing spin texture. Besides, a large electronic specific heat coefficient of up to γ ∼ 32.4 mJ mol-1 K-2 suggests FePd2Te2 is a strongly correlated metal. Our results show that FePd2Te2 is a correlated anisotropic 2D magnet that may attract multidisciplinary research interests.

Self-healing to Perfect Single Crystals via Synergistic Stabilization

Self-healing to Perfect Single Crystals via Synergistic Stabilization

Acoustic emission during approaching the critical point on stress-temperature diagram of martensitic transformation in Ni48Fe20Co5Ga27 (at.%) single crystal

Recently, the existence of martensite-austenite critical point, CP, on the stress-strain curves in the single crystalline Ni–Fe(Co)-Ga ferromagnetic shape memory alloys has been discovered by disappearance of hysteresis. It was also argued that the shear modulus at the CP and in the postcritical phase should be zero. In the present work we continue the investigation of the above new features on the “compression stress-temperature” phase diagram of the martensitic transformation (MT) of Ni48Fe20Co5Ga27 (at.%) single crystals in the vicinity of the CP by acoustic emission (AE). It is found that the AE activity (amount of events and their amplitudes) drastically dropped down by approaching the CP and tended to stabilize in a postcritical region. The above decrease is mainly due to the decrease of the number of large avalanches, while the exponents of the probability distribution of amplitudes and energies remained approximately the same, illustrating no change in the mechanism of acoustic emission events. The coordinates of the CP were estimated to be (340 ± 50) MPa and (327 ± 40) K. The elastic modulus was reduced with increasing temperature from 20 GPa down to 2 GPa in the critical region, whereby a huge total deformation of about 13 % was achieved. The stress-induced MT also shifted as a function of temperature and its slope decreased by about a factor of two upon approaching the CP. All features of the critical state determined have an obvious practical interest, as well as present a solid basis for theoretical understanding of critical and postcritical states in solids.

Crystal Facets-Activity Correlation for Oxygen Evolution Reaction in Compositional Complex Alloys.

Compositional complex alloys, including high and medium-entropy alloys (HEAs/MEAs) have displayed significant potential as efficient electrocatalysts for the oxygen evolution reaction (OER), but their structure-activity relationship remains unclear. In particular, the basic question of which crystal facets are more active, especially considering the surface reconstructions, has yet to be answered. This study demonstrates that the lowest index {100} facets of FeCoNiCr MEAs exhibit the highest activity. The underlying mechanism associated with the {100} facet's low in-plane density, making it easier to surface reconstruction and form amorphous structures containing the true active species is uncovered. These results are validated by experiments on single crystals and polycrystal MEAs, as well as DFT calculations. The discoveries contribute to a fundamental comprehension of MEAs in electrocatalysis and offer physics-based strategies for developing electrocatalysts.

Phonon excitations in Eu2Ir2O7 probed by inelastic x-ray scattering

The study of phonon dynamics and its interplay with magnetic ordering is crucial for understanding the unique quantum phases in the pyrochlore iridates. Here, through inelastic x-ray scattering on a single crystal sample of the pyrochlore iridate Eu2Ir2O7, we map out the phonon excitation spectra in Eu2Ir2O7 and compare them with the theoretical phonon spectra calculated using the density functional theory. Possible phonon renormalization across the magnetic long-range order transition is observed in our experiments, which is consistent with the results of the previous Raman scattering experiments.

Scratching properties of 4H–SiC single crystal after oxidation under different conditions

Single-crystal silicon carbide (SiC) has poor machinability because of its low fracture toughness, and surface modification has become the first choice for SiC polishing to obtain a high removal rate and a smooth surface. However, the removal mechanism of SiC after modification remains unclear. In this study, diamond scratching experiments were performed on 4H–SiC after oxidation under two conditions. To reveal the material removal mechanism, the scratch morphology and subsurface defects were analysed using Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results showed that oxidation improved the scratch depth and critical depth for ductile removal, resulting in a smooth scratch surface with low damage. However, weak oxidation increased the median crack length and exacerbated the subsurface damage. The SiOxCy, C = O, C–O–C, and Si–O–Si functional groups produced during oxidation reduced the hardness and improved the machinability of the 4H–SiC substrate. On the other hand, strong oxidation reduced the generation of surface cracks, tearing, and spalling, and weakened the propagation of subsurface median cracks. These results prove that ultrasonic-assisted photocatalytic oxidation provides high removal efficiency and defect control, providing a new approach for the synergistic polishing of SiC substrates.

High second-order nonlinearity in single-domain tetragonal PMN-PT single crystal

Recently, Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals present tremendous potential in optical applications such as Q-switches and invisible robotic devices because they possess high electro-optic properties and perfect transparency simultaneously. However, due to the difficulties in testing and sample preparation, the nonlinear optical properties of PMN-PT single crystals have not been reported yet, which poses a bottleneck for exploring its nonlinear application. In this work, a large second-order nonlinear coefficient (d31 ∼ 77.9 pm V−1) of single domain PMN-0.39PT single crystal has been revealed, which is times times higher than the maximum nonlinear coefficient of commercial LiNbO3 single crystal (d33 = 25.4 pm V−1). The complete set of nonlinear coefficients of the sample has been determined by second harmonic generation microscopy. This work presents the promising nonlinear optical property in PMN-PT single crystals and opens a door for designing high-performance nonlinear optical devices.

Stereoscopic Microscopy of Snow Crystals

Abstract Snow crystals (snowflakes) are composed of an enormous diversity of shapes that have attracted significant scientific attention over the past decades. Under the microscope, these natural structures are frequently characterized by high complexity, the detailed exploration of which requires the use of enhanced magnifications. In the work presented here, an insight into the microcosm of snow crystals is presented by application of specific light microscopy techniques. Micrographs were produced by means of a low-temperature (LT) device that prevented premature melting of the structures. Additionally, single crystals were imaged as to a stereoscopic visualization allowing the detailed spatial investigation of specific structural elements.

Surface Chemistry of Solution-Grown CsPbBr3 Single Crystals and Their Selective Cleaning for Linear-Responsive X-ray Detectors

Surface Chemistry of Solution-Grown CsPbBr₃ Single Crystals and Their Selective Cleaning for Linear-Responsive X-ray Detectors

Ultraviolet Nonlinear Optical Single Crystals of A Three-Dimensional Chiral Covalent Framework Containing Te-O-B-O Bonds.

Extending covalent organic frameworks (COFs) into crystalline carbon-free covalent backbones is an important strategy to endow these materials with more exotic functions. Integrating metal-free inorganic and organic components into one covalent framework is an effective way to address the issue of poor thermal/solvent stability in the field of nonlinear optics (NLO). However, constructing such structures is very challenging. Here, we linked 3-connected nods (BO3) and 2-connected organic building blocks (Te(Ph)2) together to produce colorless single crystals (size up to 400 µm) of a three-dimensional (3D) chiral covalent framework (CityU-22). The single-crystal X-ray diffraction (SCXRD) analysis reveals that CityU-22 has a non-carbon Te-O-B-O bond-based network with the srs topology. The chiral CityU-22 displays good stability under the treatment of different common solvents or heat (the decomposition temperature above 300 °C). Due to its non-π-conjugated backbone (-Te-O-B-O-), CityU-22 shows an ultraviolet NLO behavior with a second-harmonic generation (SHG) response similar to KH2PO4 (KDP).

Ultraviolet Nonlinear Optical Single Crystals of A Three‐Dimensional Chiral Covalent Framework Containing Te‐O‐B‐O Bonds

Extending covalent organic frameworks (COFs) into crystalline carbon‐free covalent backbones is an important strategy to endow these materials with more exotic functions. Integrating metal‐free inorganic and organic components into one covalent framework is an effective way to address the issue of poor thermal/solvent stability in the field of nonlinear optics (NLO). However, constructing such structures is very challenging. Here, we linked 3‐connected nods (BO3) and 2‐connected organic building blocks (Te(Ph)2) together to produce colorless single crystals (size up to 400 µm) of a three‐dimensional (3D) chiral covalent framework (CityU‐22). The single‐crystal X‐ray diffraction (SCXRD) analysis reveals that CityU‐22 has a non‐carbon Te‐O‐B‐O bond‐based network with the srs topology. The chiral CityU‐22 displays good stability under the treatment of different common solvents or heat (the decomposition temperature above 300 °C). Due to its non‐π‐conjugated backbone (‐Te‐O‐B‐O‐), CityU‐22 shows an ultraviolet NLO behavior with a second‐harmonic generation (SHG) response similar to KH2PO4 (KDP).

Non‐Epitaxial Electrodeposition of Overall 99% (002) Plane Achieves Extreme and Direct Utilization of 95% Zn Anode and By‐Product as Cathode

Zn anode protection in Zn‐ion batteries (ZIBs) face great challenges of high Zn utilization rate (i.e., depth of discharge, DOD) and high current density due to the large difficulty in obtaining an extreme overall RTC (relative texture coefficient) of Zn (002) plane. Through the potent interaction of Mn(III)aq and H+ with distinct Zn crystal planes under an electric field, large‐size Zn foils with a breakthrough (002) plane RTC of 99% (i.e., close to Zn single crystal) are electrodeposited on texture‐less substrates, which is also applicable from recycled Zn. The ultra‐high (002) plane RTC remarkably enhances cyclic performance of the Zn anode (70% DOD @ 45.5 mA cm‐2), and the DOD is even up to 95% (@ 28.1 mA cm‐2) with an electrolyte additive of polyaniline. Furthermore, MnO2, the by‐product of electrodeposition, is directly used as cathode of both coin cell and pouch battery, surpassing the cyclic performance exhibited by the majority of Zn||MnO2 batteries in previous instances. These results demonstrate the great potential of our strategy for high‐performance, low‐cost and large‐scale ZIBs.

Synthesis and Ligand Properties of Silsesquioxane‐Caged Phosphite T7Ph7P

AbstractThe synthesis of the phosphorus‐capped heptaphenylsilsesquioxane T7Ph7P is reported. We show that, unlike previous examples, it readily forms Lewis acid‐base adducts with boranes of different steric demand and the FeCO4 fragment. All complexes were characterized by multinuclear NMR and IR spectroscopy in solution and the solid state. The molecular structures of the adducts with BPh3 and B(C6F5)3 were determined from XRD suitable single crystals. The relative conformation of the Ph and C6F5 rings in T7Ph7P−B(C6F5)3 suggests favorable π‐interactions, stabilizing the adducts to such a degree that attempts to activate H2 or CO2 were unsuccessful.

Enhanced magnon thermal transport in yttrium-doped spin ladder compounds Sr14−xYxCu24O41

Magnons are quasiparticles of spin waves, carrying both thermal energy and spin information. Controlling magnon transport processes is critical for developing innovative magnonic devices used in data processing and thermal management applications in microelectronics. The spin ladder compound Sr14Cu24O41 with large magnon thermal conductivity offers a valuable platform for investigating magnon transport. However, there are limited studies on enhancing its magnon thermal conductivity. Herein, we report the modification of magnon thermal transport through partial substitution of strontium with yttrium (Y) in both polycrystalline and single crystalline Sr14−xYxCu24O41. At room temperature, the lightly Y-doped polycrystalline sample exhibits 430% enhancement in thermal conductivity compared to the undoped sample. This large enhancement can be attributed to reduced magnon-hole scattering, as confirmed by the Seebeck coefficient measurement. Further increasing the doping level results in negligible change and eventually suppression of magnon thermal transport due to increased magnon-defect and magnon-hole scattering. By minimizing defect and boundary scattering, the single crystal sample with x = 2 demonstrates a further enhanced room-temperature magnon thermal conductivity of 19Wm−1K−1, which is more than ten times larger than that of the undoped polycrystalline material. This study reveals the interplay between magnon-hole scattering and magnon-defect scattering in modifying magnon thermal transport, providing valuable insights into the control of magnon transport properties in magnetic materials.