共查询到20条相似文献,搜索用时 31 毫秒
1.
《Arabian Journal of Chemistry》2023,16(3):104546
Boron-rich yttrium borides are an exceptional group of compounds not only with excellent mechanical properties, but also with particular superconducting and thermoelectric properties. Although the Y–B compounds with integral components have been extensively investigated experimentally and theoretically, the yttrium borides with the fractional stoichiometries are rarely observed. Herein, utilizing a combination of the CALYPSO method for crystal structure prediction and first-principles calculations, we made an investigation on a broad range of stoichiometries of yttrium borides. An extraordinary stable Y2B5 compound possessing the fractional stoichiometry with the monoclinic P121/c1 phase is firstly uncovered. Structurally, the P121/c1-Y2B5 crystalline consists of the distorted B6 octahedrons and seven-member B rings. Remarkably, the B–B covalent network following the increment of the boron content in six concerned yttrium borides undergoes an increasing dimension, quasi one-dimensional chain → two-dimensional B ring → a combination of two-dimensional B ring and three-dimensional B6 octahedron → three-dimensional B24 cage. According to a microscopic hardness model, P121/c1–Y2B5 is considered as an incompressible and hard material with the hardness of 18.83 GPa. More importantly, Fm-3 m-YB12 can be classified into an ultra-incompressible material with the appreciable Vickers hardness of 33.16 GPa. The present consequences can provide important insights for understanding the complex crystal structures of boron-rich yttrium borides and stimulate further experimental synthesis of novel multifunctional materials with the fractional compositions. 相似文献
2.
Yu. V. Pleskov M. D. Krotova K. I. Maslakov V. P. Sirotinkin E. A. Ekimov 《Journal of Solid State Electrochemistry》2018,22(10):3129-3136
New electrode material—boron-doped synthetic carbonado (bulk polycrystalline diamond)—was synthesized at high pressures and high temperatures in the C–metal (Co, Ni, or Fe) –B growth systems. The metal borides were used as the growth medium-forming substances for graphite-to-diamond transformation at a temperature of ~?1300 °C and pressure of 8 GPa. For comparison, etalon carbonado-type electrode with nearly limiting concentration of boron in diamond was synthesized by subjecting the mixture of amorphous boron with graphite to much higher temperatures (2200–2500 °C) under the same pressure. Despite the lower content of boron in diamond synthesized in the presence of metal borides, these new boron-doped carbonado electrodes are not inferior to the etalon compact in their electrochemical activity, as judging by the onset potential of anodic chlorine evolution from KCl solution. The presence of metal-containing structural defects in boron-doped diamond matrix is supposed to be responsible for the somewhat enhanced catalytic activity of the electrodes. High-pressure synthesis of bulk metal-modified boron-doped diamond opens a new avenue in the development of superior functional electrode materials. 相似文献
3.
Rainer Telle Ai Momozawa Jochen M. Schneider 《Journal of solid state chemistry》2006,179(9):2850-2857
MAX-phases being usually composed of transition metals, group A elements and carbon/nitrogen are considered interesting materials for many applications because of their tremendous bulk modulus, “reversible” plasticity, and machinability. This is mainly due to their unique kind of bonding comprising covalent, ionic as well as metallic bonds providing “easy” planes of rupture and deformability due to the layered crystal structures.In transition metal boride systems, similar types of bonding are available. In particular the W2B5-structure type and its stacking variations allow the synthesis of strongly layered crystal structures exhibiting unique delamination phenomena.The paper presents ab initio calculations showing the similarities of bonding between the ternary carbides and the corresponding ternary or quaternary borides. Formation of boride-based nano-laminates from auxiliary liquid phases, from the melt as well as during sintering and precipitation from supersaturated solid solutions will be discussed by means of SEM and TEM studies. The role of impurities weakening the interlayer bonding will be addressed in particular. The pronounced cleavage parallel to the basal plane gives rise for crack deflection and pull-out mechanisms if the laminates are dispersed in brittle matrices such as boron carbide, silicon carbide or other transition metal borides. 相似文献
4.
Chemical Modification and Energetically Favorable Atomic Disorder of a Layered Thermoelectric Material TmCuTe2 Leading to High Performance 下载免费PDF全文
Dr. Hua Lin Hong Chen Jin‐Ni Shen Prof. Ling Chen Prof. Li‐Ming Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15401-15408
Thermoelectric (TE) materials have continuously attracted interest worldwide owing to their capability of converting heat into electricity. However, discovery and design of new TE material system remains one of the greatest difficulties. A TE material, TmCuTe2, has been designed by a substructure approach and successfully synthesized. The structure mainly features CuTe4‐based layers stacking along the c axis that are separated by Tm3+ cations. Such an intrinsic Cu site vacancy structure undergoes a first‐order phase transition at around 606 K driven by the energetically favorable uniform Cu atom re‐distribution on the covalent CuTe4‐based layer substructure, as shown by crystal structure simulations and variable‐temperature XRD data. Featured with very low thermal conductivity (ca. 0.6 W m?1 K?1), large Seebeck coefficient (+185 μV K?1), and moderate electrical conductivity (220 S cm?1), TmCuTe2 has a maximum ZT of 0.81 at 745 K, which is nine times higher than the value of 0.09 for binary Cu2Te, thus making it a promising candidate for mid‐temperature TE applications. Theoretical studies uncover the electronic structure modifications from the metallic Cu2Te to the narrow gap semiconductor TmCuTe2 that lead to such a remarkable performance enhancement. 相似文献
5.
Y. Kumashiro T. Enomoto K. Sato Y. Abe K. Hirata T. Yokoyama 《Journal of solid state chemistry》2004,177(2):529-532
The electrical properties of n-BP films newly prepared by thermal CVD in the B2H6-PH3-H2 system were improved by a deuterium lamp excitation. High-temperature electrical conductivity and thermoelectric power of amorphous boron and polycrystalline boron phosphide films grown on silica glass were measured to evaluate the thermoelectric figure-of-merit (Z). In particular, the Z-value for photo-thermal BP films was higher (10−4/K) than that of boron films, indicating that they are promising for high-temperature thermoelectric materials. 相似文献
6.
Although ZrB12 is a promising advanced material because of the boron cuboctahedron cages, the hardness of ZrB12 remains controversy. Here, we apply first-principles calculations to study the influence of transition metals (4d- and 5d-) on the hardness and thermodynamic properties of ZrB12. The calculated hardness of ZrB12 is 32.9 GPa, which is in good agreement with the previous theoretical result. Importantly, the calculated hardness of Re-doped ZrB12 is up to 40.0 GPa, which is a potential superhard material. The essential reason is that the alloying element of Re enhances the localized hybridization of B B and Zr B atoms, and then forms the strong B B covalent bond and Zr B bond. The result is well demonstrated by the chemical bonding and lattice parameter. Here, our work shows that the alloying elements of Nb, Mo, and Re enhance the thermodynamic properties of ZrB12. The Debye temperature of Re-doped ZrB12 is 1225.2 K, which is larger than that of the parent ZrB12 (1213.5 K). 相似文献
7.
Eunsoo Lee Hyounmyung Park Hyunkeun Joo Boniface P. T. Fokwa 《Angewandte Chemie (International ed. in English)》2020,59(29):11774-11778
Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V3B4 have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H2SO4) increases with increasing boron chain condensation in vanadium borides: Using a ?23 mV overpotential decrement derived from ?0.296 mV (for VB at ?10 mA cm?2 current density) and ?0.273 mV (for V3B4) we accurately predict the overpotential of VB2 (?0.204 mV) as well as that of unstudied V2B3 (?0.250 mV) and hypothetical “V5B8” (?0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical VxBy phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships. 相似文献
8.
The electrical conductivity of molten binary and ternary mixtures based on the NaF-AlF3-SiO2 system was investigated by means of a tube-cell (composed of pyrolytic boron nitride) with stationary electrodes. An impedance/gain-phase analyser (National Instruments; a high-performance modular chassis controlled by Labview? software) was used for the cell impedance measurement. The conductivity was found to vary linearly with temperature in all the mixtures investigated. The concentration dependence of electrical conductivity (isotherms) thus obtained was divided into two parts. The first represents the concentration region of up to 10 mole % of SiO2, the second the region with a higher concentration of SiO2 (from 10 mole % to 40 mole %). While the conductivity decreased considerably with the concentration of SiO2 in the second part, it increased surprisingly in the low concentration range. From these results, the influence of electrolyte composition and temperature on the electrical conductivity was examined. 相似文献
9.
Dan Zhu Yuezhen Bin Kumiko Oishi Yasuyuki Fukuda Takahiko Nakaoki Masaru Matsuo 《Macromolecular Symposia》2004,214(1):197-216
Composite films of polyethylene (PE) and polypyrrole (PPy) were prepared by polymerization of PPy on an ultradrawn polyethylene film with high modulus and high strength in ferric chloride (FeCl3) aqueous solution. The electrical conductivity of the composite film was found to be related to the polymerization conditions, such as polymerization temperature, polymerization time, the concentration and the oxidation potential of the FeCl3 solution. Scanning electron microscopy, FTIR and 13C NMR spectra were used to elucidate the morphological and structural variations of PPy prepared under different conditions, which lead to the differences in the electrical properties of the resultant composite films. The best electrical conductivity of the composite was about 5.5 S/cm for the film prepared under optimum conditions. The Young's modulus and the tensile strength reached 80 GPa and 3.2 GPa, respectively, which indicated the successful production of a conductive polymer with high strength and high modulus. 相似文献
10.
《Mendeleev Communications》2022,32(2):152-163
A review of reported data on the crystal structure, synthesis, and properties of boron suboxide B6O, which is a superhard material (hardness of up to 55 GPa, as measured in single crystals), and composites based on it is presented. Methods for the synthesis of B6O with a icosahedral structure and for the growing of crystals at high temperature and high pressure are described. The mechanical and operational characteristics of composite materials based on B6O are summarized; the resistance of B6O to oxidation is analyzed, and the properties of B6O–diamond and B6O–B4C composite materials are described. 相似文献
11.
《Journal of solid state chemistry》2004,177(4-5):1619-1623
A simple model of the bonding and doping of a series of icosahedral-boride insulators is presented. Icosahedral borides contain clusters of boron atoms that occupy the 12 vertices of icosahedra. This particular series of icosahedral borides share both the stoichiometry B12X2, where X denotes a group V element (P or As), and a common lattice structure. The inter-icosahedral bonding of these icosahedral borides is contrasted with that of B12O2 and with that of α-rhombohedral boron. Knowledge of the various types of inter-icosahedral bonding is used as a basis to address effects of inter-icosahedral atomic substitutions. The inter-icosahedral bonding is maintained when an atom of a group V element is replaced with an atom of a group IV element, thereby producing a p-type dopant. However, changes of inter-icosahedral bonding occur upon replacing an atom of a group V element with an atom of a group VI element or with a vacancy. As a result, these substitutions do not produce effective n-type dopants. Moreover, partial substitution of boron atoms for atoms of group V elements generally renders these materials p-type semiconductors. 相似文献
12.
Xiaopeng Jiao 《Journal of solid state chemistry》2010,183(7):1697-1703
Boron reacted with ball milled boron oxide under pressures between 1 and 5 GPa and at temperatures between 1300 and 1700 °C to afford boron suboxide (B6O). Icosahedral B6O grains with diameters ranging from 100 nm to 1.3 μm were prepared. The factors that affect the synthesis of B6O are investigated. The best sample with crystal size up to 1.3 μm is obtained at 2 GPa and 1400 °C for 6 h. The indentation experiment gave an average Vickers hardness of 32.3 GPa for bulk B6O sample, which is consistent with previous reports. Bulk B6O sample exhibits oxidation resistance in air up to 1000 °C and mild oxidation in the temperatures of 1000-1200 °C, which is more oxidation resistant than diamond. It is possible that B6O could be used as a substitute for diamond in industry because of its relatively mild synthesis conditions, high thermal stability and high hardness. 相似文献
13.
G. A. Bukatova S. A. Kuznetsov M. Gaune-Escard 《Russian Journal of Electrochemistry》2007,43(8):929-935
Rare-earth metal borides are widely used in different fields of modern techniques. Electrochemical synthesis at moderate temperatures
(973–1023 K) is a cost-effective alternative to direct reaction techniques. The present work reports the mechanism and kinetics
of boron and europium, boron and neodymium joint electrodischarge in chloride-fluoride molten systems. The optimum regimes
of europium and neodymium borides electrodeposition are worked out on the base of voltammetric experiments. Europium compound
is synthesized as a single-phase EuB6 product, while neodymium compounds is co-deposited as NdB4 and NdB6.
Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 8, pp. 978–984.
The article was translated by the authors. 相似文献
14.
The chitosan was prepared and mixed with some metal salts (FeCl3, Co(OAc)2 and NiCl2) by different concentrations to form chitosan-metal complexes. The metal ions which strongly complexed to the amino groups
of chitosan like Fe showed a smooth surface product, amorphous phase, thermally more stable and high electrical conductivity
than other complexes, while the Co ions which the weakly complexed with chitosan showed a rough surface product, crystalline
phase, thermally less stable and low electrical conductivity. The chitosan-metal complexes have a higher electrical conductivity
than chitosan pure at room temperature. 相似文献
15.
Masatoshi Takeda Manabu Terui Norihito Takahashi Noriyoshi Ueda 《Journal of solid state chemistry》2006,179(9):2823-2826
Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of the Seebeck coefficient decreased monotonically, while carrier mobility was almost unchanged. These results suggest that the electrical properties of the hexaboride depend largely on carrier concentration. Thermal conductivity of the hexaboride was higher than 10 W/m K even at 1073 K, which is relatively high among TE materials. Alloys of CaB6 and SrB6 were prepared in order to reduce lattice thermal conductivity. Whereas the Seebeck coefficient and electrical conductivity of the alloys were intermediate between those of CaB6 and SrB6 single phases, the thermal conductivities of the alloys were lower than those of both single phases. The highest TE performance was obtained in the vicinity of Ca0.5Sr0.5B6, indicating that alloying is effective in improving the performance. 相似文献
16.
17.
The mechanical and electrical properties of solution-processed [or gel-spun] blends of poly(3-octylthiophene) and ultrahigh molecular weight polyethylene are discussed. Tensile drawing at elevated temperatures of the phase-separated blends resulted in significant improvements of the mechanical properties, in comparison with those of the neat conducting polymer, with values of the Young's modulus reaching > 40 GPa and tensile strengths in excess of 2 GPa. Doping of the undrawn polyblend fibers with iodine vapor or FeCl3 resulted in materials of useful levels of electrical conductivity covering the full range of 10?15 to 10 S/cm. A distinct percolation threshold for electrical conductivity was not observed, even at poly(3-octylthiophene) concentrations as low as 0.5 w/w %; the electrical conductivity of the latter blend, after doping with iodine vapor, was 8 × 10?8 S/cm. 相似文献
18.
Thomas D. Bennett Dr. Jin‐Chong Tan Dr. Stephen A. Moggach Raimondas Galvelis Dr. Caroline Mellot‐Draznieks Prof. Barbara A. Reisner Dr. A. Thirumurugan Dr. David. R. Allan Prof. Anthony K. Cheetham 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(35):10684-10690
The dense, anhydrous zeolitic imidazolate frameworks (ZIFs), Zn(Im)2 ( 1 ) and LiB(Im)4 ( 2 ), adopt the same zni topology and differ only in terms of the inorganic species present in their structures. Their mechanical properties (specifically the Young’s and bulk moduli, along with the hardness) have been elucidated by using high pressure, synchrotron X‐ray diffraction, density functional calculations and nanoindentation studies. Under hydrostatic pressure, framework 2 undergoes a phase transition at 1.69 GPa, which is somewhat higher than the transition previously reported in 1 . The Young’s modulus (E) and hardness (H) of 1 (E≈8.5, H≈1 GPa) is substantially higher than that of 2 (E≈3, H≈0.1 GPa), whilst its bulk modulus is relatively lower (≈14 GPa cf. ≈16.6 GPa). The heavier, zinc‐containing material was also found to be significantly harder than its light analogue. The differential behaviour of the two materials is discussed in terms of the smaller pore volume of 2 and the greater flexibility of the LiN4 tetrathedron compared with the ZnN4 and BN4 units. 相似文献
19.
M. S. Hegde 《Journal of Chemical Sciences》2001,113(5-6):445-458
Pulsed laser deposition (PLD) is a unique method to obtain epitaxial multi-component oxide films. Highly stoichiometric, nearly
single crystal-like materials in the form of films can be made by PLD. Oxides which are synthesized at high oxygen pressure
can be made into films at low oxygen partial pressure. Epitaxial thin films of highT
c
cuprates, metallic, ferroelectric, ferromagnetic, dielectric oxides, superconductor-metal-superconductor Josephson junctions
and oxide superlattices have been made by PLD. In this article, an overview of preparation, characterization and properties
of epitaxial oxide films and their applications are presented. Future prospects of the method for fabricating epitaxial films
of transition metal nitrides, chalcogenides, carbides and borides are discussed. 相似文献
20.