12008-05-8

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Chemical Properties

cub; -60 mesh with-99.9%-purity [LID94] [CER91]

InChI:InChI=1/6B.Eu/rB6Eu/c1-7(2,3,4,5)6

Upstream product

• 16940-66-2 sodium tetrahydroborate 

Relevant academic research and scientific papers

NMR studies of EuB6 at low temperatures

We report results of 153Eu and 11B nuclear magnetic resonance (NMR) measurements on EuB6 at temperatures between 0.1 and 150 K and in external magnetic fields between H=0 and 7 T. The evolution of the 153Eu NMR spectra at low temperatures and low fields provides evidence for an unexpected and complex electronic ground state of EuB6, involving the coexistence of two magnetically very similar phases. The temperature and magnetic-field dependences of the 11B spin-lattice relaxation rate T1-1(T,H) are very well accounted for by magnon-driven relaxation. A spin-wave theoretical interpretation of the 153Eu-NMR spectra and the 11B T1-1 measurements indicate that a gap of the order of 1 K exists in the magnon excitation spectrum. 1999 The American Physical Society.

The peculiarities of the structure formation in directionally crystallized eutectics EuB6-MeB2

The possibility of producing fiber-strengthened eutectic composites in situ in the quasibinary EuB6-MeB2 (Me-Zr, Hf, Sc) alloys is shown. By directional crystallization of the eutectic composition perfect real structures on the base

Mg-assisted autoclave synthesis of RB6 (R = Sm, Eu, Gd, and Tb) submicron cubes and SmB6 submicron rods

Submicron crystalline rare-earth hexaborides (RB6; R = Sm, Eu, Gd, and Tb) have been successfully prepared by a facile one-step solid-state reaction of RCl3·OH2O, B2O3, and Mg powder in an autoclave at the relatively low temperature of 500°C. By controlling the reaction, conditions, submicronsized cubes (RB6) and rod- and needlelike SmB6 are obtained. The possible growth mechanism of the 1D SmB6 structures has also been discussed. The XRD patterns of the products show that all of the hexaborides can be indexed to a cubic phase with high crystallinity and high purity. The field-emission scanning electron microscopy (FESEM) and TEM images display their cube-, rod-, and needlelike morphologies. The selected-area electron diffraction (SAED) patterns reveal the single-crystalline nature of the products.

Densification, characterization and oxidation studies of novel TiB2+EuB6compounds

TiB2+EuB6ceramic samples with different EuB6contents were fabricated using hot -pressing technique. The introduction of EuB6promoted the sinterability, fracture toughness and oxidation resistance of TiB2. 98.7% TD achieved by adding 2.5% EuB6to TiB2by hot pressing at a relatively low temperature of 1750?°C, 35?MPa, 1h. Formation of complete solid solution of TiB2+EuB6observed for all the samples by XRD, EDS and EBSD. Hardness of all samples is measured in the range of 24–27?GPa ～50% higher fracture toughness value of 5.2?MPa?m1/2was obtained in the 2.5% EuB6contained sample compared to monolithic TiB2. Enhancement of oxidation resistance of TiB2was observed by EuB6addition due to the formation of EuBO3and Eu2O3. Oxidized cross section of TiB2+EuB6sample was measured as 340?μm, which is ～35% less than that of monolithic TiB2(520?μm), after oxidation at 1400?°C for 8h.

Chemical synthesis and microstructure of nanocrystalline RB6(R = Ce, Eu)

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.

Electrical transport properties and small polarons in Eu1-xCaxB6

Temperature- and field-dependent resistivity ρ(T,H) and Hall effect measurements have been carried out for the Eu1-xCaxB6 (x=0.2, 0.4, 0.6, and 0.9) compounds. The replacement of Eu with Ca invoked drastic changes in the ρ(T) although Ca and Eu are isoelectronic. While Eu0.8Ca0.2B6 showed a phase transition similar to that of pure EuB6, the ρ(T) of Eu1-xCaxB6 with x = 0.4 and 0.6 showed a rapid increase at low temperatures (T ≤ 10 K). The upturn of the ρ(T) was suppressed as the magnetic field increased, resulting in negative magnetoresistance (MR). For Eu0.1Ca0.9B6, the MR changed from positive at 10 K ≤ T ≤ 50 K to negative at T~2 K. It was found that the observed exotic ρ(T) is due to the change of the effective carrier density neff and Hall mobility μH determined from the Hall measurements. Analysis of the Hall mobility based on a small polaronic model showed that the carrier transport is dominated by hopping between the polaron sites in a nonadiabatic regime with four-site hopping for the Eu-rich side and three-site hopping for the Eu-poor side of the compounds. This polaronic scenario of the transport is consistent with the observed ρ(T,H), MR(T), neff(T,H), and μH(T) variation.

Magnetic properties in Ca-doped Eu hexaborides

Temperature- and field-dependent magnetization M(T,H) measurements were carried out for the series of Eu1-xCaxB6 compounds (x = 0.0, 0.13, 0.35, 0.54, 0.74, and 0.87). The small Ca doping in Eu1-xCaxB6 induced a suppression of a ferromagnetic transition temperature from Tc ' 12 K for EuB6 to Tc ' 5.5 K for Eu0.87Ca0.13B6. Interestingly, antiferromagnetic transition, rather than ferromagnetic transition, was observed in M(T) with H = 100 Oe at TN ' 4.5 K for Eu0.65Ca0.35B6 and at TN ' 3 K for Eu0.46Ca0.54B6. Temperature-dependent resistivity and specific heat data at low temperatures were presented and discussed in terms of the antiferromagnetic transition. With further increase of Ca doping, paramagnetic state was observed down to T = 2 K.

Electron doping dependence of ferromagnetism in Eu1-xLaxB6

The temperature dependent magnetization M(T) and electrical resistivity p(T) were measured to study the electron doping effect in Eu1-xLaxB6 (x=0, 0.005, 0.03, 0.05, and 0.1). At room temperature, p(T) decreases systematically with an increasing amount of electron doping. For a small doping with x=0, 0.005, and 0.03, M(T) exhibits ferromagnetic transitions and ρ(T) reduces drastically below the transition, which also reveals characteristics of double transition. It is clearly found from both M(T) and ρ(T) that the doped carriers in the region of x6. While M(T) shows a ferromagneticlike behavior at low temperature, an increase of p(T) around the ferromagneticlike region, rather than a reduction, is observed. This ρ(T) behavior looks similar to the one in SmB6, which shows the opening of a Kondo insulating gap.

Local and average crystal structure and displacements of La11B6 and EuB6 as a function of temperature

Measurements of both the average crystal structure from Rietveld refinement of neutron powder diffraction data and the local structure from La LIII-edge x-ray-absorption fine structure (XAFS) are presented for a La11B6 sample as a function of temperature (～10-320 K). These data are compared to XAFS results on a EuB6 sample. The single-site La and B positional distribution widths and the La-B and La-La bond length distribution widths and their temperature dependence are compared. This comparison allows an estimate of the La and B site displacements, and we find that these sublattices are only slightly correlated with each other. Moreover, while the temperature dependence of the displacement parameters of the average sites obtained from diffraction fit an Einstein model well, the temperature dependence of the La-B bond length distribution width requires at least two vibrational frequencies, corresponding to the La and B frequencies of the individual sites. XAFS data on EuB6 indicate that the situation is the same in the Eu compound. In addition, comparisons between data taken below and above the ferromagnetic transition temperature for EuB6 place stringent limits on the lattice involvement in the associated metal-insulator transition and the ensuing large magnetoresistance effect. This lack of lattice involvement in the magnetoresistance transition is in sharp contrast to the strong lattice involvement observed in the colossal magnetoresistance lanthanum manganese perovskites.

Electronic transport in Eu1-xCaxB6

We have measured the electrical resistivity, the magnetoresistance, the Hall effect, and the magnetization in varying temperature ranges between 0.3 and 300 K on single crystals of EuB6, CaB6, and Eu0.8Ca0.2B6. The ferromagnetic phase transition of EuB6, marked by a sharp peak in the temperature dependence of the electrical resistivity ρ(T) just below 16 K, is shown to be accompanied by a considerable increase of the effective charge carrier concentration neff. The overall features of the transport properties of Eu0.8Ca0.2B6 are similar to those of EuB6. A phase transition at 5.3 K has been established. However, the increase of neff across this phase transition by two orders of magnitude is much more pronounced than in pure EuB6. 2000 The American Physical Society.