Synthesis of the superfine high-entropy zirconate nanopowders by polymerized complex method

The high-purity and superfine high-entropy zirconate nanopowders, namely (Y0.25La0.25Sm0.25Eu0.25)2Zr2O7 nanopowders, without agglomeration, were successfully synthesized via polymerized complex method at low temperatures for the first time. The results showed that the crystallinity degree, lattice strain, and particle size of the as-synthesized powders were gradually enhanced with the increase of the synthesis temperature from 800 to 1300 °C. The as-synthesized powders involved fluorite phase in the range of 800–1200 °C while they underwent the phase evolution from fluorite to pyrochlore at 1300 °C. It is worth mentioning that the as-synthesized powders at 900 °C are of the highest quality among all the as-synthesized powders, which is due to the fact that they not only possess the particle size of 11 nm without agglomeration, but also show high purity and good compositional uniformity.

Characterization of Structural Defects in (Cd,Zn)Te Crystals Grown by the Travelling Heater Method

Structural defects and compositional uniformity remain the major problems affecting the performance of (Cd, Zn)Te (CZT) based detector devices. Understanding the mechanism of growth and defect formation is therefore fundamental to improving the crystal quality. In this frame, space experiments for the growth of CZT by the Travelling Heater Method (THM) under microgravity are scheduled. A detailed ground-based program was performed to determine experimental parameters and three CZT crystals were grown by the THM. The structural defects, compositional homogeneity and resistivity of these ground-based crystals were investigated. A ZnTe content variation was observed at the growth interface and a high degree of stress associated with extensive dislocation networks was induced, which propagated into the grown crystal region according to the birefringence and X-ray White Beam Topography (XWBT) results. By adjusting the growth parameters, the ZnTe variations and the resulting stress were efficiently reduced. In addition, it was revealed that large inclusions and grain boundaries can generate a high degree of stress, leading to the formation of dislocation slip bands and subgrain boundaries. The dominant defects, including grain boundaries, dislocation networks and cracks in the interior of crystals, led to the resistivity variation in the crystals. The bulk resistivity of the as-grown crystals ranged from 109 Ωcm to 1010 Ωcm.

Boron Influence on Defect Structure and Properties of Lithium Niobate Crystals

Defect structure of nominally pure lithium niobate crystals grown from a boron doped charge have been studied by Raman and optical spectroscopy, laser conoscopy, and photoinduced light scattering. An influence of boron dopant on optical uniformity, photoelectrical fields values, and band gap have been also studied by these methods in LiNbO3 crystals. Despite a high concentration of boron in the charge (up to 2 mol%), content in the crystal does not exceed 10−4 wt%. We have calculated that boron incorporates only into tetrahedral voids of crystal structure as a part of groups [BO3]3−, which changes O–O bonds lengths in O6 octahedra. At this oxygen–metal clusters MeO6 (Me: Li, Nb) change their polarizability. The clusters determine optically nonlinear and ferroelectric properties of a crystal. Chemical interactions in the system Li2O–Nb2O5–B2O3 have been considered. Boron, being an active element, structures lithium niobate melt, which significantly influences defect structure and physical properties of a crystal grown from such a melt. At the same time, amount of defects NbLi and concentration of OH groups in LiNbO3:B is close to that in stoichiometric crystals; photorefractive effect, optical, and compositional uniformity on the contrary is higher.

Fabrication of High-Entropy Disilicide Nanopowders via Molten Salt-Assisted Magnesium Thermal Reduction

In this work, (Nb 0.25 Ta 0.25 Ti 0.25 Hf 0.25 )Si 2 high-entropy disilicide nanopowders were successfully fabricated via molten salt-assisted magnesium thermal reduction for the first time. The results showed that the as-obtained nanopowders possessed a single hexagonal structure (TaSi 2 -type) and consisted of numerous nanopowders with an average particle size of 55 nm . These nanopowders exhibited highly compositional uniformity at microscale , but shown the aggregation of Ti element at nanoscale. In addition, a typical template formation mechanism was proposed and analyzed in detailed. This work would provide a new way to synthesis of high-entropy disilicise powders for potential high-temperature harsh environment applications.

Preparation of Zr-Al-Mo-Cu Single Targets with Glass Forming Ability and Deposition of Thin Film Metallic Glass

Generally, thin-film metal glass (TFMG) is deposited using two or more elemental targets. Thus, achievement of a homogeneous coating during mass production is difficult. As a new method of TFMG deposition, a single target with high glass-forming ability (GFA) has been used to improve the sputtering process, facilitating easy processing and broad application of sputtering targets. In this study, three kinds of targets (i.e., cast, amorphous, and crystalline targets) are prepared via casting and powder processes. The thermal and mechanical properties of the three targets prepared using the various methods are investigated, and the crystalline target is found to be the most thermodynamically and mechanically stable of the three alternatives. In addition, for TFMG deposited using the microcrystalline target, excellent compositional uniformity between the target and coating is achieved. Therefore, this study experimentally demonstrates that a fine crystalline target is most suitable for use as a multi-component single target in GFA manufacturing methods. These findings are expected to facilitate commercial use of TFMGs.

Are Large Particles of Iron Detrimental to Properties of Powder Metallurgy Steels?

It is experimentally shown that a removal of particles exceeding 100 microns in size from iron powders typically used in the fabrication of medium density powder metallurgy steels has a weak effect on apparent density, flowability and compressibility of blends as well as on density and strength of green bodies. An elimination of such particles, i.e., cutting off a heavy tail of a size distribution histogram at the 100 μm threshold, improves a compositional uniformity of sintered materials, but has no noticeable beneficial effect upon the strength of a final product, which is likely be determined by a fraction of pores and their shapes. A presence of soft pearlitic inclusions hardly matters unless their number density becomes so large that a 3D continuity (integrity) of a hard martensitic matrix is lost. This finding suggests that such an expensive preparatory step as sieving away large particles from as-received mixtures would bear no technological advantages. It was experimentally found that an attempt to lower the threshold below 100 μm noticeably worsened apparent density, flowability and compressibility.

Characterization of 2D MoS2 and WS2 Dispersed in Organic Solvents for Composite Applications

ABSTRACTIn this work, we have explored the prospects of MoS2 and WS2, both of which are semiconducting 2D materials, for potential composite applications. In order to form 2D materials composites we have to first disperse them chemically in solution. MoS2 and WS2 powders were oversaturated in N-Methyl-2-pyrrolidone (NMP) solution at 37.5 mg/mL and sonicated at room temperature (RT) for sonication times ranging from 30 minutes to close to 24 hours. After solution processing, the samples with the 2D flakes were transferred to an Isopropyl Alcohol (IPA) bath for particle size distribution analysis. We have observed significant changes in particle size distribution spanning two orders of magnitude as a function of the sonication conditions. Specifically, the observed changes in particle size distribution for MoS2 and WS2 powders ranged from 44 microns down to 0.409 microns, and 148 microns down to 0.409, respectively, as compared to the untreated materials. Structural analysis was conducted using the SEM and X-Ray diffraction. The structural analysis using the SEM revealed morphological signatures between the two materials, where the MoS2 flakes had a randomly oriented distribution with occasional triangular flakes. In the case of the WS2, regardless of the sonication conditions, the WS2 flakes seemed to have a characteristic 120° angular distribution at the vertices, representing a rhombus with concave edges. The XRD analysis showed a minute shift in the characteristic peaks that maybe due to strain-induced effects as a result of the solution processing. Optical characterization of the materials was also conducted using Raman Spectroscopy to validate the average layer number resulting from the solution dispersions and the spatial and compositional uniformity of the two material samples.