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For the first time, we report on the structural and magnetic properties of a polycrystalline sample of Ni 4 Nb 2 O 9 from I-type ( Fdd 2), obtained by the partial cosubstitution of Nb 5+ by Ti 4+ and W 6+ . The crystal structure is investigated by combining synchrotron X-ray, neutron, and electron diffraction at room temperature. This I-type structure is derived from the corundum-like Ni 4 Nb 2 O 9 II-type ( Pbcn ) and is noncentrosymmetric and polar. The Ni-lattice is composed of the stacking of distorted honeycomb layers with double zigzag ribbons 60° disoriented from each other in two successive double layers. The connection between layers is ensured by the sharing of octahedra faces building (Nb,W,Ti) 2 O 9 , Ni 2 O 9 , and Ni 3 O 12 units. This study shows how the disruption of the Nb 2 O 6 units by smaller d 0 cations impacts the structure, significantly modifying the Ni network and, thus, the magnetic properties. The latter were studied by dc- and ac-magnetic susceptibility, and the magnetic structure was solved by neutron powder diffraction. A ferrimagnetic behavior occurs below 68 K, followed by a re-entrant spin-glass-like behavior below ≈50 K.

Al 4 SiC 4 is a ternary wide-band-gap semiconductor with a high strength-to-weight ratio and excellent oxidation resistance. It consists of slabs of Al 4 C 3 separated by SiC layers with the space group of P 6 3 mc . The space group allows Si to occupy two different 2 a Wykoff sites, with previous studies reporting that Si occupies only one of the two sites, giving it an ordered structure. Another hitherto unexplored possibility is that Si can be randomly distributed on both 2 a sites. In this work, we revisit the published ordered crystal structure using experimental methods and density functional theory (DFT). Al 4 SiC 4 was synthesized by high-temperature sintering at 1800 °C from a powder mixture of Al 4 C 3 and SiC. Neutron diffraction confirmed that Al 4 SiC 4 crystallized with the space group of P 6 3 mc , with diffraction patterns that could be fitted to both the ordered and the disordered structures. Scanning transmission electron microscopy, however, provided clear evidence supporting the latter, with DFT calculations further confirming that it is 0.16 eV lower in energy per Al 4 SiC 4 formula unit than the former. TEM analysis revealed Al vacancies in some of the atomic layers that can introduce p-type doping and direct band gaps of 0.7 and 1.2 eV, agreeing with our optical measurements. Finally, we propose that although the calculated formation energy of the Al vacancies is high, the vacancies are stabilized by entropy effects at the high synthesis temperature. This indicates that the cooling procedure after high-temperature synthesis can be important in determining the vacancy content and the electronic properties of Al 4 SiC 4 .

The magnetic properties of TbMgNi 4- x Co x intermetallic compounds and selected hydrides and deuterides of this system have been studied by various techniques, including magnetic measurements, in situ X-ray and neutron powder diffraction. The intermetallic compounds crystallize in a SnMgCu 4 -type structure and magnetically order below a Curie temperature ( T C ), which increases exponentially with the Co content. This can be due to the ordering of the Co sublattice. On the other hand, the insertion of D or H in TbMgNiCo 3 strongly decreases T C . The X-ray diffraction measurements versus temperature reveal cell volume minima at T C for the compounds with x = 1-3 without any hints of the structure change. The analysis of the neutron diffraction patterns for the intermetallics with x = 2 and 3 indicates a slightly canted ferrimagnetic structure below T C . The Tb moments refined at 16 K are 4.1(2) μ B /Tb for x = 2, and 6.2(1) μ B /Tb for x = 3, which are smaller than the free ion value (9.5 μ B /Tb). This reduction can be due to the influence of temperature but also reveals the crystal field effect. As Ni and Co occupy statistically the same Wyckoff site, an average Ni/Co moment was refined, leading to 1.7(2) μ B /atom for x = 2 and 1.8(1) μ B /atom for x = 3 at 16 K. This moment is slightly canted compared to the Tb moment., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

High-entropy materials, with complex compositions and unique cocktail characteristics, have recently drawn significant attention. Additionally, a family of sodium super ion conductors (NASICONs)-structured phosphates in energy storage areas shows a comprehensive application for traditional alkaline ion batteries and, in particular, solid-state electrolytes. However, there is no precedent in fabricating this kind of NASICON-type high-entropy phase. Here, we report the successful fabrication of two well-crystallized high-entropy phosphates, namely, Na 3 (Ti 0.2 V 0.2 Mn 0.2 Cr 0.2 Zr 0.2 ) 2 (PO 4 ) 3 (HE-N 3 M 2 P 3 ) and Na(Ti 0.2 V 0.2 Mn 0.2 Cr 0.2 Zr 0.2 ) 2 PO 4 O x (HE-NMP). The prepared materials in which the transition metals (TMs) of Ti, V, Mn, Cr, and Zr occupy the same 12c Wykoff position can form a structure analogous to R 3̅ c Na 3 V 2 (PO 4 ) 3 that is carefully determined by X-ray diffraction, neutron diffraction, and transmission electron microscopy. Further, their performance for sodium ion batteries and sodium-based solid-state electrolytes was evaluated. The HE-N 3 M 2 P 3 might exhibit a promising electrochemical performance for sodium storage in terms of its structure resembling that of Na 3 V 2 (PO 4 ) 3 . Meanwhile, the HE-NMP shows considerable electrochemical activity with numerous broad redox ranges during extraction and insertion of Na + , related to the coexistence of several TM elements. The evaluated temperature-dependent ionic conductivity for HE-NMP solid electrolyte varies from 10 -6 to 10 -5 S cm -1 from room temperature to 398.15 K, offering high potential for energy storage applications as a new high-entropy system.

Due to their superb mechanical properties and high specific mass, tungsten heavy alloys are used in demanding applications, such as kinetic penetrators, gyroscope rotors, or radiation shielding. However, their structure, consisting of hard tungsten particles embedded in a soft matrix, makes the deformation processing a challenging task. This study focused on the characterization of deformation behavior during thermomechanical processing of a WNiCo tungsten heavy alloy (THA) via the method of rotary swaging at various temperatures. Emphasis is given to microstrain development and determination of the activated slip systems and dislocation density via neutron diffraction. The analyses showed that the grains of the NiCo2W matrix refined significantly after the deformation treatments. The microstrain was higher in the cold swaged sample (44.2 × 10 -4 ). Both the samples swaged at 20 °C and 900 °C exhibited the activation of edge dislocations with <111> {110} or <110> {111} slip systems, and/or screw dislocations with <110> slip system in the NiCo2W matrix. Dislocation densities were determined and the results were correlated with the final mechanical properties of the swaged bars.

Advanced thermomechanical hot rolling is becoming a widely used technology for the production of fine-grained spring steel. Different rapid phase transformations during the inductive heat treatment of such steel causes the inhomogeneous mixture of martensitic, bainitic, and austenitic phases that affects the service properties of the steel. An important task is to assess the amount of retained austenite and its distribution over the cross-section of the inductive quenched and tempered wire in order to evaluate the mechanical properties of the material. Three different analytical methods were used for the comparative quantitative assessment of the amount of retained austenite in both the core and rim areas of the sample cross-section: neutron diffraction-for the bulk of the material, Mössbauer spectroscopy-for measurement in a surface layer, and the metallographic investigations carried by the EBSD. The methods confirmed the excessive amount of retained austenite in the core area that could negatively affect the plasticity of the material.