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Superconducting wires are widely used in fabricating magnetic coils in fusion reactors. In consideration of the stability of 11B against neutron irradiation and lower induced radio-activation properties, MgB2 superconductor with 11B serving as boron source is an alternative candidate to be used in fusion reactor with severe irradiation environment. In present work, a batch of monofilament isotopic Mg11B2 wires with amorphous 11B powder as precursor were fabricated using powder-in-tube (PIT) process at different sintering temperature, and the evolution of their microstructure and corresponding superconducting properties was systemically investigated. Accordingly, the best transport critical current density (Jc) = 2 × 104 A/cm2 was obtained at 4.2 K and 5 T, which is even comparable to multi-filament Mg11B2 isotope wires reported in other work. Surprisingly, transport Jc vanished in our wire which was heat-treated at excessively high temperature (800 °C). Combined with microstructure observation, it was found that lots of big interconnected microcracks and voids that can isolate the MgB2 grains formed in this whole sample, resulting in significant deterioration in inter-grain connectivity. The results can be a constructive guide in fabricating Mg11B2 wires to be used as magnet coils in fusion reactor systems such as ITER-type tokamak magnet. [ABSTRACT FROM AUTHOR]

Abstract: The phase stability of the two TiO2 modifications (anatase and rutile) in fumed SiO2/TiO2 nano-composites (0–24.8 wt-% silica) under thermal and hydrothermal conditions was investigated by X-ray powder diffraction, transmission electron microscopy (TEM) and gas adsorption methods (BET). The results show that the phase transformation from anatase to rutile type of structure and the growth of anatase crystallites are significantly retarded by mixing small amounts of SiO2 into TiO2, while the specific surface area is maintained. The SiO2/TiO2-composites reveal a remarkable shift in the anatase to rutile transformation temperature from approx. 500 °C (pure TiO2) to approx. 1000 °C (samples with SiO2 contents of more than 10%). The rate of phase transformation from anatase to rutile is enhanced under hydrothermal conditions compared to conventional thermal treatment, e.g. pure titania (AEROXIDE® TiO2 P25) annealed under hydrothermal conditions (100 g/m3 absolute humidity, 4 h at 600 °C) had a rutile content of 85%, while the same specimens annealed in absence of humidity contained only 46% rutile. However, the difference in rate of phase transformation became less pronounced when the silica content in SiO2/TiO2-composites was further increased. TEM results showed that the surface of the anatase crystallites was covered with silica. This averts coalescence of anatase crystallites and keeps them under a critical size during the annealing process. When the crystal domains grew larger, a rapid conversion to rutile took place. The critical size of anatase crystallites for the phase transformation was estimated to be 15–20 nm. [Copyright &y& Elsevier]

Abstract: A set of Fe3+-modified PbTiO3 nanopowders has been synthesized according to the combined polymerization and pyrolysis (CPP) route of metallorganic precursors [Erdem E, Böttcher R, Semmelhack H-C, Gläsel H-J, Hartmann E, Hirsch D. Preparation of lead titanate ultrafine powders from combined polymerisation and pyrolysis route. J. Mater. Sci. 2003;38:3211–7] with subsequent calcination at various temperatures. X-ray diffraction verifies the formation of a PbTiO3 perovskitic phase and Raman-spectroscopy proves the existence of ferroelectricity. Furthermore, the prevailing defect structure has been investigated by means of electron paramagnetic resonance (EPR) spectroscopy. The EPR results clearly indicate marked size effects by approaching to the critical grain size ( nm) at which a size-driven tetragonal-to-cubic phase transition is observed at room temperature. As a function of mean grain size, either defect dipoles or ‘isolated’ defects (, ) are formed. These results are analyzed in terms of a core–shell model. Accordingly, the obtained Fe3+-modified PbTiO3 nanoparticles consist of a ferroelectric core, a distorted interface region, and a cubic dead layer which is paraelectric. [Copyright &y& Elsevier]

Abstract: This paper provides a detailed description of the preparation and characterization of diffusion-doped Cr2+:ZnSe and Fe2+:ZnSe. In the experiments, Cr2+:ZnSe samples with peak absorption coefficients (1775nm) of as high as 74cm−1 and fairly good spatial uniformity were obtained. In the case of Fe2+:ZnSe, samples with a maximum absorption coefficient of 11.6cm−1 at 2400nm were synthesized. A three-dimensional analytical diffusion model was further developed to determine the diffusion coefficient D from absorption data. At 1000°C, D was determined to be 5.4×10−10 cm2/s and 7.95×10−10 cm2/s for Cr2+:ZnSe and Fe2+:ZnSe, respectively. In the case of Cr2+:ZnSe, we employed an alternative technique to determine the diffusion coefficient from position-dependent absorption data taken with a Cr4+:YAG laser. With this method, the temperature variation of D was further measured in the 800–1100°C temperature ranges. [Copyright &y& Elsevier]

Yellow, transparent single crystals of Ba3[BN2]2 (P212121 (No. 19), a=424.73(2), b=1105.60(4) and c=1475.72(6) pm, Z=4) are obtained by the reaction of Ba2N and BN in arc-welded Nb ampoules at 1300 K. The title compound crystallizes, despite its familiar 3:2:4 stoichiometry, in a new structure type. The vibrational spectra of orthorhombic Ba3[BN2]2 have been measured and assigned. The IR spectrum reveals strong band splitting arising from the low site symmetry and the presence of two different sets of crystallographically independent [BN2]3−groups. The new structure and the vibrational data are compared with those previously reported for the cubic form of Ba3[BN2]2. [Copyright &y& Elsevier]

Sub-micron sized TiB 2 ceramic powders were prepared via self-propagating high-temperature synthesis (SHS) followed by HCl leaching at different temperatures. Purified powders obtained using optimum process parameters were consolidated by field assisted sintering technology/spark plasma sintering (FAST/SPS) technique. Phase and microstructural analyses of both the powder and sintered samples were carried out by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The chemical analyses and particle size measurements of the specimen were conducted by inductively coupled plasma-mass spectrometry (ICP-MS) and dynamic light scattering (DLS) techniques. The final properties of the sintered sample were determined in terms of density and microhardness. The effects of different HCl leaching temperatures on the formation, microstructure, particle size, purity and sintering behavior of the SHS-produced TiB 2 powders were investigated. The SHS reaction of TiO 2 -B 2 O 3 -Mg powders as a starting mixture yielded MgO, Mg 3 (BO 3 ) 2 and Mg beside the desired phase TiB 2 . All three magnesium containing by-products were completely removed by performing hot HCl leaching. TiB 2 powders after SHS reaction and leaching with 9.3 M HCl for 30 min at 80 °C revealed a minimum purity of 98.4% and a homogenous particle size distribution with an average particle size of 536 nm. In the ultimate SPS experiment which was conducted at 1500 °C for 5 min under a pressure of 50 MPa, a relative density of 94.9% and a micro-hardness value of 24.56 GPa were achieved. [ABSTRACT FROM AUTHOR]

Cover Feature: The First Alkaline-Earth Azidoaurate(III), Ba[Au(N3)4]2 - 4 H2O (Chem. Eur. J. 11/2023) Alkaline-earth metals, azides, crystal structures, gold, vibrational spectroscopy Keywords: alkaline-earth metals; azides; crystal structures; gold; vibrational spectroscopy EN alkaline-earth metals azides crystal structures gold vibrational spectroscopy 1 1 1 02/23/23 20230221 NES 230221 B Dark orange and highly explosive b : The cover figure displays the structure of cation-poor Ba[Au-(N SB 3 sb ) SB 4 sb ] SB 2 sb B - b 4 H SB 2 sb O, containing tetraazidoaurate(III)anions with a novel geometry and gold in a square-planar coordination of nitrogen. [Extracted from the article]

A novel europium (III) nitridoborate, Eu 3 [B 3 N 6 ], was successfully synthesized by oxidation of Eu 3 II [BN 2 ] 2 with Br 2 at 1073 K. The compound crystallizes in the trigonal space group R 3 ¯ c (No:167) with a =11.9370(4) Å, c =6.8073(4) Å, and Z =6. The crystal structure of Eu 3 [B 3 N 6 ] consists of isolated, planar cyclic [B 3 N 6 ] 9– units which are charge-balanced by Eu 3+ cations. The oxidation state of Eu was investigated by Mössbauer spectroscopy, electron spin resonance (ESR) spectroscopy, and quantum chemical calculations. The 151 Eu Mössbauer spectroscopic measurement at 77 K reveals that the main signal at δ=0.93(7) mm/s is originating from trivalent Europium. Eu 3 [B 3 N 6 ] showed no ESR signal in accordance with a non-magnetic ( J =0) 7 F 0 ground state of the 4 f 6 configuration. Quantum chemical calculations find six electrons in the 4 f subshell (4 f 6 ) of Eu indicating an oxidation state of +3. We present for the first time the vibrational spectra of a compound with cyclic trimer [B 3 N 6 ] 9− moieties. The Raman spectrum of Eu 3 [B 3 N 6 ] is in good agreement with the predicted number of modes for the spectroscopically relevant cyclic [B 3 N 6 ] 9− group with D 3 h symmetry. [ABSTRACT FROM AUTHOR]

Undoped and aluminum (Al) doped magnesium diboride (MgB2) samples were synthesized using a high-temperature solid-state synthesis method. The microscopic defect structures of Al-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman spectroscopy, and electron paramagnetic resonance. It was found that Mg-vacancies are responsible for defect-induced peculiarities in MgB2. Above a certain level of Al doping, enhanced conductive properties of MgB2 disappear due to filling of vacancies or trapping of Al in Mg-related vacancy sites. [ABSTRACT FROM AUTHOR]