One-step synthesis of ThMn12-type Sm0.8Zr0.2Fe11SiBx (x = 0–0.2) ribbon magnets via rapid solidification

The Nd2Fe14B-based permanent magnets are fabricated by rapid solidification, powder metallurgy and hydrogen treatment methods, production relaying heavily on strategic rare-earth raw materials. Considerably cheaper due to lower demand, Ce and La drew attention as substitutes for resource-critical Nd in Nd2Fe14B-based alloys to obtain cost-efficient magnets of intermediate performance, between hard ferrites and Nd2Fe14B. The isomorphous Ce2Fe14B and La2Fe14B tetragonal compounds have inferior intrinsic magnetic properties therefore substitution of Ce or La for Nd in the Nd2Fe14B compound lowers the maximum achievable, theoretical performances. Furthermore, in practical alloys, depending on concentration, solubility, solidification rate and processing regimes, replacing Nd with Ce or La induces changes in the Nd2Fe14B phase (Φ-phase) crystal lattice and in the alloy phase composition and microstructure, affecting the intrinsic (composition-dependent) and extrinsic (microstructure-dependent) magnetic properties. The partitioning of the substitution element between the Φ-phase and the intergranular phase(s) impacts the saturation magnetization and the Curie temperature of the Φ-phase. Through the variation of the Nd2Fe14B cell constants the interatomic distances change and impact on the magnetic Fe-Fe ion exchange interaction with effects on the Curie temperature. Segregations like CeFe2 Laves-type phase and primary α-Fe occurring in the alloys reduce the Φ-phase relative fraction which decreases the remanent magnetization. Microstructure alterations in grain structure like excessive grain growth and in the distribution of the intergranular material like a discontinuous intergranular phase negatively impact the coercivity. In this thesis, rapid solidification by melt-spinning and strip-casting was chosen for alloy synthesis, followed by melt-spun powder hot-working (hot-pressing followed by hot-deformation) and hydrogen treatment of strip-cast alloys (decrepitation and HDDR (hydrogenation disproportionation desorption recombination)). High solidification rates restrict phase segregations and produce fine grained microstructures (nanosized in melt-spun ribbons and down to a few microns in strip-cast flakes). Hot-working is performed for densification and crystallographic c-axis texture development through grain deformation to enhance the remanence. At this stage, the segregation of the substitution element in the Nd-rich intergranular eutectic phase is shown to change its melting behavior thus influencing the melt-spun alloy's deformability. The HDDR treatment was employed for grain refinement and texture inducement to produce anisotropic powders. The phase structure and microstructure evolutions through processing stages, from as-cast to hydrogen decrepitated, disproportionated and recombined states are comprehensively analyzed in relation to the Ce concentration in the strip-cast alloys, with a focus on the grain boundary processes. The transformation of the CeFe2 intergranular segregations to amorphous CeFe2Hx upon hydrogen absorption, decomposition into CeHx and α-Fe upon heating and redistribution among the hard matrix phase play a supportive role in coercivity development through HDDR treatment.

Mg0.5Zr2(PO4)3 is a priority electrolyte for Mg solid state batteries. However, it is difficult to achieve high density and phase purity simultaneously, especially in thin films. Here, we processed liquid-feed flame spray pyrolysis synthesized MZPFex nanopowders to make transparent films via simple pressureless sintering at 1100°C. The influence of Fe on the phase and microstructure are discussed. In particular, dense and high phase purity Mg0.6Fe0.2Zr1.8(PO4)3 exhibits extremely low ionic area specific resistance, 1.6 kΩ cm2. This paper presents an effective method to prepare dense, high phase purity solid electrolytes at modest sintering temperatures.

High cubic phase purity and growth mechanism of cubic InN thin-films by Migration Enhanced Epitaxy

Achieving both high efficiency and long-term stability is the key to the commercialization of perovskite solar cells (PSCs)1,2. However, the diversity of perovskite (ABX3) compositions and phases makes it challenging to fabricate high-quality films3-5. Perovskite formation relies on the reaction between AX and BX2, whereas most conventional methods for film-growth regulation are based solely on the interaction with the BX2 component. Herein, we demonstrate an alternative approach to modulate reaction kinetics by anion-π interaction between AX and hexafluorobenzene (HFB). Notably, these two approaches are independent but work together to establish 'dual-site regulation', which achieves a delicate control over the reaction between AX and BX2 without unwanted intermediates. The resultant formamidinium lead halides (FAPbI3) films exhibit fewer defects, redshifted absorption and high phase purity without detectable nanoscale δ phase. Consequently, we achieved PSCs with power conversion efficiency (PCE) up to 26.07% for a 0.08-cm2 device (25.8% certified) and 24.63% for a 1-cm2 device. The device also kept 94% of its initial PCE after maximum power point (MPP) tracking for 1,258 h under full-spectrum AM 1.5 G sunlight at 50 ± 5 °C. This method expands the range of chemical interactions that occur in perovskite precursors by exploring anion-π interactions and highlights the importance of the AX component as a new and effective working site to improved photovoltaic devices with high quality and phase purity.

Generative shaping and material-forming (GSM) enables structure engineering of complex-shaped Li4SiO4 ceramics based on 3D printing of ceramic/polymer precursors

Fabrication of Li4SiO4 ceramic pebbles with uniform grain size and high mechanical strength by gel-casting

Ruddlesden-Popper reduced-dimensional hybrid perovskite (RDP) semiconductors have attracted significant attention recently due to their promising stability and excellent optoelectronic properties. Here, the RDP crystallization mechanism in real time from liquid precursors to the solid film is investigated, and how the phase transition kinetics influences phase purity, quantum well orientation, and photovoltaic performance is revealed. An important template-induced nucleation and growth of the desired (BA)2 (MA)3 Pb4 I13 phase, which is achieved only via direct crystallization without formation of intermediate phases, is observed. As such, the thermodynamically preferred perpendicular crystal orientation and high phase purity are obtained. At low temperature, the formation of intermediate phases, including PbI2 crystals and solvate complexes, slows down intercalation of ions and increases nucleation barrier, leading to formation of multiple RDP phases and orientation randomness. These insights enable to obtain high quality (BA)2 (MA)3 Pb4 I13 films with preferentially perpendicular quantum well orientation, high phase purity, smooth film surface, and improved optoelectronic properties. The resulting devices exhibit high power conversion efficiency of 12.17%. This work should help guide the perovskite community to better control Ruddlesden-Popper perovskite structure and further improve optoelectronic and solar cell devices.

For decades solidification of highly undercooled alloy melt has been widely studied [1–6]. The study of that is meaningful for two reasons. First, high undercooling (1T ) before solidification can lead to rapid solidification once the melt nucleates, which results in refined microstructures and improved properties. Second, the relative slowly cooled but highly undercooled melt opens up the possibilities of direct observations of the rapid solidification processes under nonequilibrium conditions, which is important both to the consummation of rapid solidification theory and to the optimum of production techniques. If the undercooling of alloy melts and directional solidification technology are combined organically, we will obtain a simple solidification model of rapid solidification of highly undercooled alloy melt. That is valuable both in the quantitative research of solidification of highly undercooled melts and in the production of materials which require aligned crystal orientation with much less time and expenses. Tarshis et al. [7] have studied the microstructures of Cu-Ni alloy solidified at different initial undercoolings. They found that coarse and dendritic microstructures could exist in an undercooling range, from 85 K to 150 K. Beyond this undercooling range equiaxed structures were found. Lux et al. [8] demonstrated the feasibility of producing superalloy castings having directional microstructures from undercooled melt. Ludwig et al. [9] developed a so-called autonomous directional solidification technology and obtained single crystal superalloy turbine blades from undercooled superalloy CMSX-6 melt. Schwarz et al. [10] proposed a mechanism which described the observed transitions in solidification of undercooled melts from a coarse grained dendritic to a grain refined equiaxed microstructure. It was thought that the refinement was caused by remelting and coarsening of primary formed dendrites. Research team of DLR [11, 12] had done much work on the triggered rapid solidification of highly undercooled electromagnetically levitated alloy melt. They observed the microstructures which grew radially from the trigger point. Kiminami and Sahm [13] had studied the undercooling and subsequent solidification of Pd77.5Cu6Si16.5 alloy melt. Also they obtained the radial microstructures which grew from the nucleation point. However, detailed studies about the directional solidification from highly undercooled melts are still scarce. In this paper, directional solidification and rapid solidification from highly undercooled alloy melt are combined using a Cu-5wt.%Ni alloy in a set of selfmade experimental apparatus, therefore, rapid directional solidification from highly undercooled alloy melts are realized, and expected directional solidified structures are obtained. The experiments were divided into two stages. First, undercooling of Cu-5wt.%Ni alloy melt; second, the rapid directional solidification of highly undercooled Cu-5wt%Ni alloy. The 810 mm Cu-5wt %Ni master alloy ingots were prepared from 99.972% Cu and 99.99% Ni in an induction furnace using a graphite crucible under vacuum, then the ingots were cut into pieces with cylindric shape weighing about 5 g (the surface layers of the ingots were cut off in advance). Fig. 1a shows the apparatus used during the first experimental stage. A procedure to get high undercooling, which has been employed effectively in a number of investigations [4–6], was applied by superheating and cooling the molten metal several times whether immersed in a molten high purity B2O3 glass or not (both in a high purity fused silica tube). High frequency induction melting technology was employed here. When the power was off, the sample began to cool and reached its maximum undercooling. The temperature was measured with an infrared thermometer with precision of ±1.0%. Before measurement it was calibrated by standand WRe3-WRe25 thermocouples under the similar experimental conditions as the subsequent undercooling and directional solidification experiments. Fig. 1b shows a sketch of the self-made apparatus used during the directional solidification experiments of undercooled Cu-5wt.%Ni alloy melts. The sample obtained during the first experimental stage was remelted in a funnel-like quartz crucible with 8 4 mm in diameter and formed a liquid cylinder. Because of the electromagnetic levitation force and the surface tension the melt could be held in the crucible. Then when the melt was undercooled to a predetermined undercooling, liquid Ga-In-Sn alloy (it was at room temperature) was used to nucleate the undercooled melt. Then rapid directional solidification would occur in the undercooled melt. The actual undercooling was determined according to the recorded cooling curve. Solidified samples

Improvement in phase purity and yield of hydrothermally synthesized smectite using Taguchi method

Investigations on gold nanoparticles supported on rare earth oxide catalytic materials

From metamaterial to metasurface and metadevice, the artificial structure with sub-wavelength scale on diverse platforms offers the ability to shape light in a custom way. The optical fiber is a robust and flexible media that has seen wide applications in optical communications, optical sensing, microscopy, and endoscope imaging. Here, we consider metasurface on a large-core fiber platform for twisting light. Using the designed and fabricated meta-facet fiber, we demonstrate (i) the excitation of both linearly polarized and circularly polarized twisted light (OAM+1, OAM−1) from either meta-facet side or planar-facet side, (ii) phase-front reconstruction of twisted light simply from a tilt interferogram using the Fourier-transform method, and (iii) ultra-broadband response from 1480 to 1640 nm with high phase purity above 93% for twisting light. The demonstrations on meta-facet fiber for twisting ultra-broadband light with high phase purity may open up perspectives to more emerging applications in information, biology, and medical science.

Phase purity, particle size and its distribution contributes a lot to the physical properties of M-type hexa-ferrites. These parameters are strongly influenced by the variation in synthesis parameters. In the present work, effect of synthesis parameters such as molar ratio (Fe/Sr) and volume rate of addition of precipitating agent on M-type hexa-ferrite (SrFe12O19) prepared by co-precipitation method have been investigated systematically. The molar ratio (Fe/Sr) in SrFe12O19 was varied as 12, 11, 10, 09, and 08. X-ray diffraction analysis revealed that molar ratio does not affect the phase purity. X-ray diffraction analysis of the samples prepared with different volume rate of addition of precipitating agent indicated that phase purity and micro-structural properties of SrFe12O19 are greatly influenced by the above synthesis parameter. High volume rate of addition of precipitating agent resulted in high phase purity, smaller particle size, and narrow particle size distribution.

To improve the electrochemical performances of high voltage LiCoMnO4 spinel cathode material at 5.3 V, Cr doped LiCoMn1-xCrxO4 (x = 0, 0.025, 0.050, 0.075) materials were synthesized by a one-step solid-state at 750°C. Rietveld refinement results showed that the phase purity of spinel is promoted with the increase in Cr concentration, which can be explained by the strong CrO bond that reduces oxygen deficiency and eliminates Li2MnO3 impurity phase during the synthesis process. Such change in phase purity further causes the improvement in specific capacity, and the 5.0%Cr doped sample displays the best result with a value of 123.0 mAh/g at 0.1°C and 93.3 mAh/g at 10°C. For a comparison, the pristine sample only releases a capacity of 112.6 mAh/g at 0.1°C and 54.8 mAh/g at 10°C. Improved capacity retention, from 83.1% to 90.1% after 100 cycles at 1°C, is also observed due to the suppressed volume change during the redox process after the incorporation of Cr cations in the lattice. Promoted rate performance, attributed from the improved Li ion diffusion coefficient, is also confirmed in the experiment. The improvement of those electrochemical properties could be explained by high-phase purity and superior structural stability benefited from Cr-doping. Novelty statement LiCoMn1-xCrxO4 (x = 0, 0.025, 0.050, 0.075) materials were synthesized by a one-step solid-state at 750°C, Chromium had been confirmed to reduce oxygen loss during LiCoMnO4 synthesis due to high oxygen affinity of Cr, which improves phase purity. As a result, the specific capacity was increased. Cr-doping enhances the structural stability so that capacity retention was promoted due to higher bond energy of CrO than MnO; rate performance was also enhanced due to the improved diffusion coefficient.

Low-toxic gelcasting of zircon ceramics

ABSTRACTLi4SiO4 pebbles are widely selected as attractive ceramic tritium breeding materials for the test blanket modules (TBM) of international thermonuclear experimental reactor (ITER). In this work, SiO2 coating approach was first employed to synthesize precursor powders for fabricating the Li4SiO4 pebbles. Lithium source and silicon source were mixed by hydrolyzing tetraethyl orthosilicate (TEOS) in the Li2CO3 solution. Compared with the traditional solid state method, the precursor powders synthesized by SiO2 coating approach displayed distinct coating structure, which was able to effectively lower the phase formation temperature and the sintering temperature of Li4SiO4 pebbles, and then decrease the grain size of Li4SiO4 pebbles. Thermogravimetry and different scanning calorimetry (TG-DSC) and X-ray diffraction (XRD) analyses indicate that the phase formation temperature of Li4SiO4 synthesized by SiO2 coating approach is far below that of the conventional solid state reaction. Then, wet method was employed to prepare green spheres with the as-prepared precursor powders. Finally, Li4SiO4 pebbles with small grain size (average value 1.12 µm), high phase purity, good sphericity, and uniform microstructure could be obtained by sintering the green spheres at a low temperature of 625°C, which are expected to show favorable tritium release behavior and be used as tritium breeding materials for blankets.