In this study, the low-temperature reduction-diffusion (LTRD) process using a Li-Ca reductant, which has a low eutectic point of about 230 °C, was demonstrated. The RD reaction was possible at a very ...low temperature of 400 °C significantly less than 850 °C, which is the lowest practicable temperature of the conventional RD process, by identifying the production of the SmFe2 phase. The LTRD process in this study also made it possible to investigate the Sm-Fe binary phases synthesized at the low temperature and the Sm-Fe phase transitions depending on the temperatures with the compositions of Sm and Fe.
TbCu7-type Sm-Fe-N anisotropic powder with a high Fe content has the potential to surpass the Nd-Fe-B magnet. In this study, elemental substitution of Sm in a Sm-Fe system was investigated for the ...purpose of synthesizing Fe-rich TbCu7-type Sm-Fe compounds using a low-temperature reduction-diffusion (LTRD) process, which is a synthesis method capable of producing TbCu7-type Sm-Fe-N anisotropic powder. Sm-X-Fe powders have been synthesized by mixing ɑ-Fe, SmCl3, one chloride of additives (X = Zr, Hf, Y, Dy, La, Ce and Nd), Ca, and LiCl, and performing the reduction-diffusion reaction at 600 °C. The results of an EDX analysis and the variation of a-axis lengths of the TbCu7-type Sm-X-Fe phase suggested that all additional elements could be substituted for Sm. Although the synthesis of Fe-rich TbCu7-type phase was not achieved in this study, substitution of Zr and Hf showed a potential to increase Fe content.
In this study, the temperature of the low-temperature reduction-diffusion (LTRD) process was successfully decreased to below 600 °C by introducing LiCl-KCl eutectic molten salt with a low eutectic ...point (352 °C) as a solvent for Ca reductant. Therefore, the Sm-Fe binary compounds, which were synthesizable at previously-unexplored low temperatures by the LTRD process using LiCl-KCl eutectic molten salt, were investigated, including whether a new metastable or ThMn
12
-type Sm-Fe binary phase was formed. The Sm-Fe phase transitions of the Sm-Fe binary compounds at a low temperature were identified, and it was found that MgCu
2
-type Sm-Fe, PuNi
3
-type Sm-Fe and TbCu
7
-type Sm-Fe phases were synthesized and stable at 400, 500 and 550 °C respectively. Although no new metastable Sm-Fe and ThMn
12
-type Sm-Fe compounds were discovered in this study, this work can demonstrate that it is possible to synthesize the Sm-Fe phase at very low temperatures by the LTRD process for the first time.
Graphical Abstract
Multielement rare earth (R)-transition metal (T) intermetallics are arguably the next generation of high-performance permanent magnetic materials for future applications in energy-saving and ...renewable energy technologies. Pseudobinary Sm
2
Fe
17
N
3
and (R,Zr)(Fe,Co,Ti)
12
(R = Nd, Sm) compounds have the highest potential to meet current demands for rare-earth-element-lean permanent magnets (PMs) with ultra-large energy product and operating temperatures up to 200°C. However, the synthesis of these materials, especially in the mesoscopic scale for maximizing the maximum energy product (
), remains a great challenge. Nonequilibrium processes are apparently used to overcome the phase-stabilization challenge in preparing the R-T intermetallics but have limited control of the material's microstructure. More radical bottom-up nanoparticle approaches based on chemical synthesis have also been explored, owing to their potential to achieve the desired composition, structure, size, and shape. While a great achievement has been made for the Sm
2
Fe
17
N
3
, progress in the synthesis of (R,Zr)(Fe,Co,Ti)
12
magnetic mesoscopic particles (MMPs) and R-T/T exchange-coupled nanocomposites (NCMs) with substantial coercivity (
) and remanence (
, respectively, remains marginal.
It was predicted that TbCu7-type Sm-Fe powder prepared by the low-temperature reduction-diffusion (LTRD) process using a Li-Ca reductant would contain no residual ɑ-Fe because this reductant would ...not produce the absorbed water that hinders the reaction between Sm and Fe by forming oxychlorides when molten salt is used as the reductant. Contrary to this expectation, a detailed microstructure analysis revealed that a residual phase of unreacted ɑ-Fe existed in some TbCu7-type Sm-Fe particles rather than as separate Fe particles. This residual ɑ-Fe phase was not located in the center of the Sm-Fe particles and was not detected in some Sm-Fe particles, suggesting that the reason for the residual ɑ-Fe phase is inhomogeneous diffusion of Sm into the Fe due to slow diffusion at low temperatures. Although this TbCu7-type Sm-Fe powder contained a small amount of unreacted ɑ-Fe phase, the magnetic properties of the nitride TbCu7-type Sm-Fe were also estimated.
•The possibility synthesizing single-phase TbCu7-type Sm-Fe powder was investigated.•The residual α-Fe phase was smaller than in the case using molten salts.•ɑ-Fe phases are not located in the center of some TbCu7-type Sm-Fe particles.•It is inferred that the reduced Sm was inhomogeneously diffused into the Fe.•The coercivity of the TbCu7-type Sm-Fe-N powder was estimated as Hc = 5.5 MA·m-1
Although Li-BNICs (lithium boron nitride intercalation compounds) have been successfully synthesized by heat treatment, their crystal structures are still not clearly understood and controversial. In ...this study, several hypothetic phases of Li-BNICs are postulated and their phase stabilities are calculated through applying DFT (density functional theory), a common tool in first principles calculations. According to the experimental results on Li-BNICs, disordered structures have been suggested, which is also analyzed by introducing VCA (virtual crystal approximation) method for a disorder calculation. Lattice parameters, formation energies and electronic band structures for hypothetic Li-BNICs are estimated, where the VCA disorder calculation agrees well with experimental results, exhibiting negative formation energies. Li(BN)9 and Li(BN)3 are suggested as possible phases for Li-BNICs.
•The crystal structures and phase stabilities of Li-BNICs are studied using DFT.•VCA disorder calculation agrees well with experimental results.•Disorder calculation of 1L-model Li-BNICs showed negative formation energy.•Disordered 1L-model Li(BN)9 and Li(BN)3 phases are the highest possibility of exist.•Band structures of 1L-model Li-BNICs (disorder calculation) and Li-GICs are similar.
Hexagonal boron nitride (h-BN) has been explored for lithium intercalation due to its similar crystal structure to graphite, a well-known anode material for Li-ion secondary batteries. Lithium h-BN ...intercalation compounds (Li-BNICs) have been successfully synthesized through heat treatment. In this study, potential physical properties related to electrical conductivity were investigated using pristine and milled h-BN, which is further mixed/combined with milled graphite. The electrochemical properties were characterized by cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL). The chemical potential of h-BN was estimated about 1.0V versus Li/Li+ and a two-phase reaction was suggested. Accordingly, Li-BNIC is more stable than Li-GICs (lithium graphite intercalation compounds) in terms of thermal stability.
•Electrochemical Li intercalation of pristine and 2.5h-milled h-BN is firstly studied.•Chemical potential of h-BN versus Li/Li+ was estimated about 1.0V.•Li-BNIC is more stable than Li-GICs in terms of thermodynamics.•Li intercalation of BN is more difficult than of graphite by electrochemical process.•Li intercalation is improved by inducing defects in BN through milling.
Hexagonal boron nitride (h-BN) exhibits a layered solid structure such as graphite, and the h-BN intercalation compounds (BNICs) have been actively studied as with graphite intercalation compounds ...(GICs). It is difficult, however, to synthesize BNICs compared with GICs, where the synthesis of BNICs requires high temperature and/or pressure. In this study, the Li-BNIC is synthesized by ball milling and heat treatment, and the samples were characterized by X-ray diffractomety (XRD), differential thermal analysis (DTA) and 7Li NMR (nuclear magnetic resonance) study.
New XRD peaks corresponding to Li-BNICs were observed from the milled sample after heat treating at 700 °C for 2 h. The shifted peaks of h-BN to the lower angles imply an expanded BN lattice through Li insertion. The exothermic DTA peaks observed between 200 and 500 °C might be the synthesis temperatures of Li-BNIC. The NMR spectra of the Li-BNIC are modified according to the ratio of Li to BN, although the corresponding XRD patterns are not changed.
•Lithium boron nitride intercalation compound is synthesized by the sequential process of ball milling and heat treatment.•The structures are studied by X-ray diffractomety, 7Li nuclear magnetic resonance and the Rietveld analysis.•Inserting Li atoms into hexagonal BN exhibits consistent lattice expansion regardless of the Li/BN ratio.•The intercalated Li atoms exhibit two-dimensional irregular arrangement in the Li-BNIC structure.
Recently, intercalation compounds with various intercalants between hexagonal boron nitride (h-BN) layers have been studied, where lithium BN intercalation compound (Li-BNIC) is one of such compounds ...successfully synthesized. They are expected to exhibit similar properties to lithium graphite intercalation compounds (Li-GICs) that are known as the anode material for lithium ion batteries. It is difficult, however, to apply Li-BNIC for the batteries due to its returning to an insulator when Li is deintercalated. In this study a Li–BN–graphite ternary system has been focused because it is reported that graphite-like BC2N is a promising material for rechargeable Li batteries. The primary purpose of this study is thus to investigate combined reactivity of BN and graphite with Li through milling and heating processes, and possible intercalation of Li into the matrix: h-BN, graphite or BCN. The pieces of lithium metal, h-BN and graphite powders were ball-milled using a vibratory ball-mill machine and heat-treated at 700 °C for 2 h under argon atmosphere. The samples were then characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, 7Li nuclear magnetic resonance and Differential thermal analysis study. Li-GICs were mainly produced by milling, while post-annealing caused their eliminations and instead produced Li-BNICs with small amount of other lithium compounds. In terms of thermal stability, Li-BNIC is more stable than Li-GICs. In a Li–BN–graphite system, an activation energy of Li-BNIC was estimated to be 119.6 kJ/mol, which is higher than reported activation energies for Li-GICs.
•Li, h-BN and graphite were ball-milled and sequentially heat-treated.•Li atoms were intercalated into graphite by milling, while deintercalated by heating.•Li atoms were intercalated into h-BN by milling and sequential heat treatment.•BN and graphite did not react in either process.•Li-BNIC is more stable than Li-GIC, while the activation energy is larger.
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