- Chemical synthesis and microstructure of nanocrystalline RB6(R = Ce, Eu)
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Nanocrystalline RB6(R = Ce and Eu) have been successfully synthesized by a solid-state reaction of CeO2and Eu2O3with NaBH4at a temperature range of 900-1200 °C. Phase composition, grain morphology, microstructure and valence states of RB6were investigated by using XRD, FESEM, HRTEM and XANES measurements. Results show that all the synthesized hexaborides are composed of single-phase nanoparticles with cubic morphology. The FFT patterns of HRTEM images reveal that the hexaborides have a high crystallinity with CaB6-type cubic structure. The present preparation technique is as a novel and invaluable for the developments of highly crystallized RB6nanoparticles.
- Lihong, Bao,Wurentuya,Wei, Wei,Yingjie, Li,Tegus
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- Mechanochemical Synthesis of High Crystalline Cerium Hexaboride Nanoparticles from CeO2-B2O3-Mg Ternary System
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High crystalline cerium hexaboride (CeB6) nanoparticles (NPs) were synthesized using mixture of magnesium (Mg), cerium oxide (CeO2) and boron oxide (B2O3) via the mechanochemical process at room temperature. Based on the results, magnesiothermic reduction of B2O3 occurred after about 2 h of milling in a mechanically induced self-sustaining reaction (MSR). The significant amount of heat produced by the reduction reaction resulted in CeO2 reduction to elemental Ce which finally reacted with elemental B and formed CeB6 compound. According to XRD analyses, the degree of crystallinity and lattice parameter of the product was calculated about 93 % and 4.1458 ?, respectively. The morphology observations revealed that the synthesized CeB6 had semi-cubic shape with the range of size 25-60 nm. The synthesis of CeB6 during the thermal treatment was studied by simultaneous thermal analysis (STA) technique. It was found that the reduction of B2O3 took place after melting of Mg meanwhile, no CeB6 phase achieved even up to 1100 °C.
- Torabi, Omid,Naghibi, Sanaz,Golabgir, Mohammad-Hossein,Jamshidi, Amin
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- SYNTHESIS OF CERIUM AND GADOLINIUM BORIDES USING BORON CAGE COMPOUNDS AS A BORON SOURCE.
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Cerium borides (CeB//4 and CeB//6) and gadolinium borides (GdB//4 and GdB//6) were synthesized using boron cage compounds M//2(B//1//0H//1//0)//3 (M equals Ce and Gd) as a boron source. A mixture of hexaboride (CeB//6 or GdB//6) and amorphous boron was formed by thermal decomposition above 1000 degree C or 1200 degree C, respectively. These borides contained a small amount of inclusions (oxides, borates, etc. ) which can be removed by acid treatment in HCl solution with the formation of single phases.
- Itoh, H.,Tsuzuki, Y.,Yogo, T.,Naka, S.
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- Direct low-temperature synthesis of RB6 (R=Ce, Pr, Nd) nanocubes and nanoparticles
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Rare-earth hexaborides (RB6, R=Ce, Pr, Nd) nanocrystals were prepared by a facile solid state reaction in an autoclave. Single-crystalline RB6 nanocubes were fabricated at 500 °C starting from B2O3, RCl3/s
- Zhang, Maofeng,Wang, Xiaoqing,Zhang, Xianwen,Wang, Pengfei,Xiong, Shenglin,Shi, Liang,Qian, Yitai
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- Single-crystal x-ray diffraction study on Ce1-xLaxB6 solid solutions
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Single crystals of Ce1-xLaxB6, with x = 0, 0.25, 0.50 and 0.75, prepared by crystallization from solutions in molten aluminium, were investigated by X-ray diffraction. Experimental data were corrected for thermal diffuse s
- Blomberg,Merisalo,Korsukova,Gurin
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- On phase equilibria and crystal structures in the systems Ce-Pd-B and Yb-Pd-B. Physical properties of R2Pd13.6B5 (R=Yb, Lu)
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Phase equilibria and crystal structures of ternary compounds were determined in the systems Ce-Pd-B and Yb-Pd-B at 850 °C in the concentration ranges up to 45 and 33 at% of Ce and Yb, respectively, employing X-ray single crystal and powder diffraction. Phase relations in the Ce-Pd-B system at 850 °C are governed by formation of extended homogeneity fields, τ2-CePd8B2-x (0.103-Ce3Pd25-xB8-y (1.063Bx (03. Crystallographic parameters for the new structure type τ2-CePd8B2-x (space group C2/c, a=1.78104(4) nm, b=1.03723(3) nm, c=1.16314(3), β=118.515(1)° for x=0.46) were established from X-ray single crystal diffraction. The crystal structures of τ2-CePd8B2-x and τ3-Ce3Pd25-xB3-y are connected in a crystallographic group-subgroup relationship. Due to the lack of suitable single crystals, the novel structure of τ1-Ce6Pd47-xB6 (x=0.2, C2/m space group, a=1.03594(2) nm, b=1.80782(3) nm, c=1.01997(2) nm, β=108.321(1)°) was determined from Rietveld refinement of X-ray powder diffraction data applying the structural model obtained from single crystals of homologous La6Pd47-xB6 (x=0.19) (X-ray single crystal diffraction, new structure type, space group C2/m, a=1.03988(2) nm, b=1.81941(5) nm, c=1.02418(2) nm, β=108.168(1)°). The Yb-Pd-B system is characterized by one ternary compound, τ1-Yb2Pd14B5, forming equilibria with extended solution YbPd3Bx, YbB6, Pd5B2 and Pd3B. The crystal structures of both Yb2Pd14B5 and isotypic Lu2Pd14B5 were determined from X-ray Rietveld refinements and found to be closely related to the Y2Pd14B5-type (I41/amd). The crystal structure of binary Yb5Pd2-x (Mn5C2-type) was confirmed from X-ray single crystal data and a slight defect on the Pd site (x=0.06) was established. The three structures τ1-Ce6Pd47-xB6, τ2-CePd8B2-x and τ3-Ce3Pd25-xB8-y are related and can be considered as the packings of fragments observed in Nd2Fe14B structure with different stacking of common structural blocks. Physical properties for Yb2Pd13.6B5 (temperature dependent specific heat, electrical resistivity and magnetization) yielded a predominantly Yb-4f13 electronic configuration, presumably related with a magnetic instability below 2 K. Kondo interaction and crystalline electric field effects control the paramagnetic temperature domain.
- Sologub, Oksana,Rogl, Peter,Salamakha, Leonid,Bauer, Ernst,Hilscher, Gerfried,Michor, Herwig,Giester, Gerald
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- Solar control dispersions and coatings with rare-earth hexaboride nanoparticles
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Nanoparticle dispersions of rare-earth hexaborides have been prepared using a media agitation mill and have been examined for optical properties. High visible light transmittance coupled with strong absorption in the near-infrared (NIR) wavelengths suitable for solar control windows are reported for hexaboride nanoparticle dispersions with particle size dependence and the effect of artifacts. Nanoparticulate LaB6 shows the largest NIR absorption among rare-earth hexaborides. NIR absorption is considered to arise from the free electron plasmon resonance. On decreasing the particle size below 120 nm, both visible light transmittance and NIR absorption are found to increase gradually until the size of 18-26 nm when they reach the maximum, and then decrease again at below 18 nm. Zirconia contamination and formation of lanthanum oxide were found to be involved during the milling process, leading to small additional absorptions around 300 and 650 nm, respectively.
- Takeda, Hiromitsu,Kuno, Hiroko,Adachi, Kenji
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- Ab initio structure determination of new boride CePt3B, a distorted variant of CaTiO3
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X ray powder diffraction and electron probe micro-analysis were used to determine the crystal structure of a ternary boride CePt3B, tetragonal in structure. The presence of two phases were identified through Rietveld refinement on the sample. Ce was found to be in a trivalent state in the compound. Magnetic susceptibility measurements also showed that the compound did not order magnetically at 2 K.
- Sologub,Hester,Salamakha,Leroy,Godart
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- Thermodynamic properties of the rare earth borides and carbides in a wide temperature range
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For the first time a systematic study was made of the heat capacity and enthalpy of the rare earth tetra- and hexaborides and sesqui- and dicarbides in the temperature range 60-2300 K.
- Bolgar, A. S.,Muratov, V. B.,Blinder, A. V.,Kryklya, A. I.,Suodis, A. P.
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- Single-crystalline CeB6 nanowires
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Considered to be one of the best electron emission materials, CeB6 nanowires are of great scientific and industrial interest. CeB6 nanowires of square cross section with about 50 nm in lateral dimension and more than several micrometers in length have been successfully produced using a chemical vapor deposition method. The nanowires are grown in the lattice direction, and both the tip top and the side surfaces are terminated with the {100} lattice planes. Copyright
- Zhang, Han,Zhang, Qi,Tang, Jie,Qin, Lu-Chang
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- The system Ce-Zn-B at 800 °c
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The isothermal section for the system CeZnB has been established at 800 °C using electron microprobe analysis and X-ray powder diffraction. No ternary compounds exist and mutual solid solubilities of binary phases are negligible. In the concentration range of 10.010.5 at% Ce two structural modifications have been confirmed: high temperature βCe2Zn 17 above ～750 °C with the Th2Zn17 type (R3m, a=0.90916(4) nm, c=1.3286(1) nm) and low temperature αCeZn 7 (Ce1-xZn52x; x～0.33) up to 750 °C for which we attributed the TbCu7 type (P6/mmm, a=0.52424(2), c=0.44274(1) nm). The crystal structure of CeZn7 was derived from the Rietveld refinement of X-ray powder intensities. Precise data on atom site distribution and positional parameters have been furthermore provided from X-ray single crystal refinements for two compounds, for which crystal structures hitherto have only been derived from X-ray diffraction photographs: Ce 3Zn11 (Immm, a=0.45242(2) nm, b=0.88942(3) nm, c=1.34754(4) nm) and Ce3Zn22 (I41/amd; a=0.89363(2) nm, c=2.1804(5) nm).
- Malik,Sologub,Giester,Rogl
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- Enhanced grain refinement of in situ CeB6/Al composite inoculant on pure aluminum by microstructure control
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In situ CeB6/Al composite has been proven to be an effective refiner for commercial pure aluminum, however, it remains unclear as to the mechanisms of synthesis and grain refinement. We use low-temperature alloying and high-speed melt spinning
- Liu, Shuiqing,Wang, Xin,Cui, Chunxiang,Zhao, LiChen,Li, Nuo,Zhang, Zhe,Ding, Jinhua,Sha, Denghao
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- Preparations of lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6)
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Due to strong anti-poisoning ability, good emission stability, high emission current density, lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6) have been maturely applied in electron emission emitter. In this paper, a new manufacturing method for LaB6 (or CeB6) powder was proposed by using La2O3 (or CeO2), B4C, and Al as raw materials. After high-temperature reaction in the range of 1673–1773?K and the following alkaline leaching at 90°C, LaB6 or CeB6 powder with particle size of about 10?μm was obtained. Furthermore, by Al metal flux method, the obtained powder was used to manufacture single crystal block with size of several millimeters.
- Wang, Yu,Chou, Kuo-Chih,Zhang, Guo-Hua
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p. 1954 - 1966
(2021/11/24)
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- High-Pressure Synthesis of Light Lanthanide Dodecaborides (PrB12 and CeB12): Effects of Valence Fluctuation on Volume and Formation Pressure
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Light lanthanide dodecaborides, RB12 (R = Pr and Ce), were synthesized from a stoichiometric mixture of hexaborides and boron using a laser-heated diamond anvil cell under high-pressure and high-temperature conditions. Contrary to the expectation that lighter lanthanide elements require higher pressure to crystallize RB12, in situ X-ray diffraction experiments reveal that cerium dodecaboride crystallizes at 26 GPa, which is significantly lower than that required to form the heavier praseodymium dodecaboride (35 GPa). In addition to the lower formation pressure, an anomalous volume reduction is also observed in CeB12, which can be explained by a valence fluctuation between Ce3+ and Ce4+ indicated by X-ray absorption near-edge structure measurements. A polyhedral coordination change from a truncated cube in RB6 to a truncated octahedron in RB12 and associated shortening of the R-B bond length result in an increase in bulk modulus and hardness.
- Yusa, Hitoshi,Iga, Fumitoshi,Fujihisa, Hiroshi
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p. 2568 - 2575
(2022/02/10)
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- Destabilization of LiBH4 by (Ce, La)(Cl, F)3 for hydrogen storage
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The mixtures of LiBH4 with halides of Ce or La in a molar ratio of 3:1 were investigated to explore their hydrogen storage properties. The ball milling of LiBH4 with chloride of Ce or La yielded Ce(BH 4)3 and La(BH4)3, while fluoride of Ce or La did not react with LiBH4 during extended ball milling at room temperature. The dehydrogenation temperatures of the ball-milled mixtures were reduced to 220-320 °C, which were much lower than that of pure LiBH4. The diborane emission during hydrogen release was observed at a low level. The dehydrogenation temperature is found to be affected by the composition of rare earth halides, but less influenced by ball milling time. The endothermic dehydrogenation reactions produced lithium halides, hydrides and borides of the corresponding rare earth element. Moreover, the LiBH4 + 1/3(Ce, La)(Cl, F)3 showed partial reversibility through the formation of an unknown borohydride, allowing for a potential hydrogen storage system.
- Zhang, Bang Jie,Liu, Bin Hong,Li, Zhou Peng
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p. 751 - 757
(2011/02/24)
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- Thermoelectric properties of some metal borides
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Polycrystalline AlMgB14 and some hexaborides (CaB6, SrB6, YbB6, SmB6, and CeB6) were synthesized to examine their thermoelectric properties. Single phase of orthorhombic AlMgB14, which contains B12 icosahedral clusters as building blocks, was obtained at sintering temperatures between 1573 and 1823K. Seebeck coefficient (α) and electrical conductivity (σ) of the phase were about 500μV/K and 10-11/Ωm at room temperature, respectively. These values are comparable to those of metal-doped β-rhombohedral boron. On the other hand, metal hexaborides with divalent cation possessed large negative α ranging from -100 to -270μV/K at 1073K. Calculated power factors of CaB6 and SrB 6 exceeded 10-3W/K2m within the entire range of temperature measured. As a result, they can be thought as promising candidates for n-type thermoelectric material.
- Takeda, Masatoshi,Fukuda, Tadahiro,Domingo, Ferrer,Miura, Takahiro
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p. 471 - 475
(2008/10/09)
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