12008-21-8Relevant articles and documents
The effect of Sm-doping on optical properties of LaB6 nanoparticles
Chao, Luomeng,Bao, Lihong,Shi, Junjie,Wei, Wei,Tegus,Zhang, Zhidong
, p. 618 - 621 (2015)
Nanocrystalline particles of LaB6, SmB6 and Sm-doped LaB6 have been prepared by a solid-state reaction in order to investigate the optical properties of ternary rare-earth hexaborides. The sizes of prepared nanoparticles range from dozens to more than 200 nm, as confirmed by XRD, SEM and TEM examinations. The optical property concerning the absorption spectra was tested with ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectrum. All samples exhibit high absorbance in NIR range and UV range. The increase of Sm-doping amount shifts the position of minimum absorptance value of LaB6 to the long-wave direction. Density functional theory (DFT) is employed to interpret the optical properties of Sm-doped LaB6, and results indicate that Sm 4f states change the DOS at near Fermi surface of LaB6 after Sm doping and the reduced number of conduction electrons results into the change of absorption spectra.
Unique preparation of hexaboride nanocubes: A first example of boride formation by combustion synthesis
Kanakala, Raghunath,Rojas-George, Gabriel,Graeve, Olivia A.
, p. 3136 - 3141 (2010)
Nanocubes of LaB6 and Sm0.8B6 have been synthesized using low-temperature combustion synthesis, a technique that had only been used previously for the preparation of oxides. The hexaboride nanocubes were prepared using lanthanum nitrate or samarium nitrate, carbohydrazide, and boron powders. The furnace temperature for synthesis was kept at 320°C, lower than the typical temperature values used in combustion processes for the preparation of oxides. After synthesis, the nanocubes were characterized using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The combustion process was analyzed using differential scanning calorimetry, which shows that the formation of the carbohydrazide and nitrate melts as well as the formation of a complex between metal ions and carbohydrazide are crucial steps for the reaction. The technique results in high-purity powders with a unique cubic morphology, in which the corners of the cubes can be used as point sources for efficient electron emission
Peculiarities of electronic, phonon and magnon subsystems of lanthanum and samarium tetraborides
Novikov,Mitroshenkov,Matovnikov
, p. 906 - 911 (2015)
Abstract Experimental research was carried out to study the temperature dependences of heat capacity Cp(T = 2-300 K), lattice parameters a(T), and c(T), (5-300 K) of lanthanum and samarium tetraborides. A comparison with data obtained previously for LuB4 reveals the peculiar influence of lanthanide contraction and the rare-earths mass on the thermodynamic properties of rare earth tetraborides at low and high temperatures. Sharp anomalies were found in the heat capacity and thermal expansion for SmB4 at TN = 25.1 K, conditioned by the phase transition into antiferromagnetic state. The more poorly defined heat capacity anomaly around 7 K is referred to the quadrupole orbital fluctuation of the atomic magnetic moments for Sm3+ ions. The electronic, lattice, and magnetic contributions to the heat capacity and thermal expansion of samarium tetraboride were defined. Our approach makes it possible to adequately approximate the lattice components of heat capacity and thermal expansion by combining the Debye and Einstein contributions, which are based on the joint analysis of calorimetric and X-ray data. The influence of the frustration of the atomic magnetic moment system for Sm3+ ions on the thermodynamic characteristics of the samarium tetraboride magnetic phase transition was revealed.
Low temperature carbothermal and boron carbide reduction synthesis of LaB6
Hasan, Muhammad,Sugo, Heber,Kisi, Erich
, p. 176 - 182 (2013)
Rare-earth hexaborides are widely used as thermionic emitters however their economic production for large scale applications such as solar thermionic electricity generation is hampered by a need to synthesise them at lower temperature without post-synthesis cleaning treatments. Two simple synthesis techniques for producing pure lanthanum hexaboride (LaB6), carbothermal reduction using La2O3-boroncarbon and boron carbide reduction using La2O3-B4C blends respectively were studied. Using fine grained starting materials and a mild pre-milling treatment, the carbothermal method was found to produce high-purity LaB6 at a temperature 1400 °C or below. The B4C method also appeared from XRD and SEM analyses of abraded surfaces to produce high-purity LaB6 at 1400 °C however EDS maps of polished cross-sections revealed the presence of unreacted B4C necessitating a temperature of 1450 °C to complete the reaction. XRD and SEM analyses indicate that the mean particle sizes of LaB6 using the boron carbide method (220 nm) is smaller than that for the carbothermal reduction method (600 nm). The finer grains of samples prepared via the boron carbide method result in a partially sintered powder. LaB6 prepared in this way is shown to have a Richardson work function of 2.64 eV.
A solvothermal approach for the preparation of nanostructured carbide and boride ultra-high-temperature ceramics
Kelly, James P.,Kanakala, Raghunath,Graeve, Olivia A.
, p. 3035 - 3038 (2010)
The use of a solvothermal process for the synthesis of tantalum carbide (TaC) and lanthanum hexaboride (LaB6) powders in fused-quartz test tubes is reported in order to demonstrate the synthesis of these powders using thermal and chemical ignition techniques and to prove that the process is of a self-propagating high-temperature synthesis type, obviating the need for an autoclave. X-ray powder diffraction showed phase pure powders with crystallite sizes of 25 and 80 nm, while dynamic light scattering showed average particle sizes of 97 and 130 nm, for TaC and LaB6, respectively. The data demonstrates that the powders have a very low level of agglomeration. Scanning electron microscopy shows that the TaC powders have a spherical morphology, while the LaB6 powders have a mixture of cubic and spherical morphologies.
Phonon structure of LaB6 by point-contact spectroscopy
Kunii, Satoru
, p. 361 - 366 (1988)
The differential resistance dV/dI versus voltage characteristics is studied for point-contacts between a LaB6-needle on one side and a LaB 6 (100)-cleavage surface on the other. A technique of automatic in situ cleaning is used to clean the sample surface. The spectra of pure metal point-contacts are contrary to that of the tunneling contacts interposed by the oxide layer, that is, the former is for the barrierless junction of enough clean surface and the latter is for the barrier-type junction of intentionally oxidized surface. The measurements of the second derivative d 2K/dI2 give the information on the phonon density of states of LaB6, adding new experimental results on the current neutron scattering experiment. The peaks of the phonon density of states of LaB6 are situated at 12, 24, 38 and 50 meV.
A low-temperature route for the synthesis of nanocrystalline LaB6
Zhang, Maofeng,Yuan, Liang,Wang, Xiaoqing,Fan, Hai,Wang, Xuyang,Wu, Xueying,Wang, Haizhen,Qian, Yitai
, p. 294 - 297 (2008)
Nanocrystalline lanthanum hexaboride (LaB6) with mean particle size of 30 nm has been successfully synthesized at 400 °C in an autoclave starting from metallic magnesium powder, NaBH4 and LaCl3. In this case, by using B2O3 instead of NaBH4, LaB6 nanocubes with mean size of ～200 nm were formed at 500 °C. The X-ray diffraction (XRD) pattern can be indexed as cubic LaB6 with the lattice constant of a=4.151 A for LaB6 nanoparticles and 4.154 A for LaB6 nanocubes. An atomic ratio of La and B as 1:5.94 was determined from EDS for LaB6 nanoparticles. XPS data of LaB6 nanocubes indicate the atomic ratio of La to B as 1:5.95. Raman spectra indicate the formation of LaB6.
Low-temperature synthesis of nanosized metal borides through reaction of lithium borohydride with metal hydroxides or oxides
Pan, Wei Yuan,Bao, Qian Wen,Mao, Yang Jun,Liu, Bin Hong,Li, Zhou Peng
, p. 666 - 672 (2015)
In this study, we report a novel and facile synthesis approach of boron-rich transition metal borides such as LaB6 and TiB2 through reaction of lithium borohydride (LiBH4) with corresponding metal hydroxide or oxide at temperatures below 600 °C. A fast endothermic reaction occurred at around 350 °C in the ball milled mixture of 6LiBH4 + La(OH)3 or 12LiBH4 + La2O3, efficiently producing crystalline LaB6 nanoparticles of a size smaller than 100 nm. In comparison, the reaction of LiBH4 with TiO2 proceeded within a wide temperature range from 120 °C to 500 °C, resulting in the formation of nanocrystalline TiB2 of only a few nanometers. This synthesis method proved to be a facile and general route to fabricate nanosized transition metal borides.
Development of chemically synthesized spherical plasmonic LaB6 nanoparticles for biomedical applications
Wang, Yu,Fang, Chao,Li, Xiang,Li, Zhou Peng,Liu, Bin Hong
, p. 757 - 767 (2019)
LaB6 is a unique plasmonic material, for which the localized surface plasmon resonance (LSPR) absorption band intrinsically lies in the near infrared (NIR) region. In this work, we synthesized spherical LaB6 nanoparticles with a tunable size within 50–200 nm. The optical properties of these LaB6 nanospheres were found to be sensitive to the thickness of surface oxide layer that was formed during the synthesis, purification and dispersion processes. In order to enhance the stability of LaB6 nanoparticles in aqueous environment, LaB6@SiO2 with a core-shell structure was successfully prepared. Both LaB6 and LaB6@SiO2 demonstrated low cytotoxity in biomedical tests when their concentrations were limited to 0.2 mg mL?1. The in vitro photothermal therapy experiment showed that 4T1 cancer cells were eventually apoptotic after being exposed to a 980 nm laser for 5 min at a considerably low power density of 0.82 W cm?2 and a low dose of 0.1 mg mL?1 for LaB6@SiO2. The results suggest that these LaB6 nanospheres are viable photothermal agents for biomedical applications.
Single-crystalline LaB6 nanowires
Zhang, Han,Zhang, Qi,Tang, Jie,Qin, Lu-Chang
, p. 2862 - 2863 (2005)
Lanthanum hexaboride nanowires produced by chemical vapor deposition are single-crystalline and grown along the [111] direction. Streaks appearing in the electron diffraction spots indicate the lateral direction perpendicular to the nanowire growth axis.
