CeB6 Research Articles

Potential plasma facing materials: A case study on CeB6 particulate reinforced W–1Ni matrix composites produced via different sintering techniques

Tungsten (W) is the most promising material for future plasma-facing materials. Its alloys or composites reinforced with various compounds have been studied to improve the irradiation resistance of W. This study aimed to investigate the effect of boron-containing reinforcement in the W matrix against He+ ion irradiation. Cerium hexaboride (CeB6) particulates, which have high neutron shielding properties, were incorporated into the W matrix pre-alloyed by 1 wt% Ni (W1Ni). CeB6 powders were home-made and prepared from CeO2/Mg/B2O3 powder blends via mechanochemical synthesis and purification steps. 1, 5, and 10 wt% CeB6 powders were added to pre-alloyed W1Ni by mechanical alloying, and then they were consolidated by using pressureless sintering (PS, 1400 °C, 1 h) and spark plasma sintering (SPS, 1410 °C, 1 min) techniques. CeB6 particle-reinforced W1Ni composites contained different amounts of reinforcements were prepared by two different sintering methods and were compared with respect to their compositional, microstructural, and microhardness properties and wear and irradiation behaviors. Based on the results, increasing the CeB6 reinforcement amount in the composite triggered the formation of the W2B phase, especially in the W1Ni–10CeB6 composite after both sintering methods. The mechanical and irradiation properties were enhanced more by increasing the CeB6 amount in the case of using the SPS method. When compared to other sintered samples, the SPS'ed W1Ni–10CeB6 composite has the lowest specific wear rate of ∼4 × 10−7 mm3/Nm and the maximum hardness value of ∼21 GPa. According to surface deformation, the W1Ni–5CeB6 composite exhibited comparatively higher resistance to He+ ion irradiation.

Near-ultraviolet photodetector using cerium hexaboride alloy

This article investigates a new type of heterostructure photodetector (PD) made of cerium hexaboride (CeB6) and tungsten (W) alloy deposited on top of a nitrogen-doped silicon carbide substrate. Density function theory (DFT) suggests that the alloy with 67% CeB6 and 33% W provides an optimal photo response for the PD. The optimum alloy thickness is computed numerically using particle swamp optimization (PSO) in lumerical Finite difference time domain (FDTD) software, and the alloy is fabricated using direct current (DC) and radio frequency (RF) sputtering. The performance of the PD is experimentally characterized, and our findings show a maximum photocurrent of 71.86 nA and a maximum responsivity of 94.1 µAW−1 at the near ultraviolet (UV) wavelength of 405 nm.

Enhanced electrical characteristics of Zr/diamond Schottky barrier diode with cerium hexaboride interfacial layer

To fabricate a performance-enhanced Schottky barrier diode (SBD) on a diamond, a cerium hexaboride (CeB6) interfacial layer was introduced between the diamond and the Zr/Au electrode. The inserted CeB6 layer was characterized using X-ray photoelectron spectroscopy. Introducing the CeB6 layer significantly improved the performance of the diamond SBD compared with a sample without the layer. The ideality factor (n)/SBH (ΦB) values of the SBD with and without the CeB6 interlayer were 2.24/1.92 eV and 2.82/1.65 eV, representing an improvement of 20.5% and 16.4% for the ideality factor and Schottky barrier height, respectively. The reverse breakdown voltage increased from −86 to −110.5 V, indicating an improvement of 28.5% for breakdown voltage. Additionally, the reverse current of the SBD with CeB6 was suppressed, making it more reliable and stable than that without CeB6 before the breakdown threshold. The carrier concentration and depletion layer width were increased from 1.135 × 1014 cm−3 and 206.7 nm to 2.646 × 1014 cm−3 and 227.6 nm, respectively, with the introduction of CeB6. These results demonstrate the advantages of inserting of CeB6 in vertical diamond SBDs and show the potential of SBDs for future power rectifiers.

Field emission characterization of nanoFEAs on single crystal CeB6 surface fabricated by focused ion beam milling

The field emission tip arrays with sub-100 nm apices (nanoFEAs) on single crystal cerium hexaboride (CeB6) surface were fabricated by the focused ion beam (FIB) milling microtechnology. The surface morphologies and field emissions of the nanoFEAs are systematically characterized. FIB milling, similar to the physical stripping process, can fabricate the nanoFEAs single crystal CeB6 with uniform morphologies. The nanoFEAs with sharp tips of size about 50 nm demonstrate the lowest turn-on electric fields (2.0 V/[Formula: see text]m), as well as a high current ([Formula: see text]1 mA) at the field of 6.7 V/[Formula: see text]m and a high stable emission current. Such excellent performances make CeB6 nanoFEAs promising candidates for application in field emission electronics.

Electrical properties of cerium hexaboride gate hydrogen-terminated diamond field effect transistor with normally-off characteristics

Fabrication of hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with low work function cerium hexaboride (CeB6) gate material has been successfully performed. For the 8 μm gate length device, the threshold voltage (VTH) is extracted to be −0.46 V, demonstrating a normally-off characteristics. The maximum drain source current density (IDmax) is −83.8 mA/mm, and the competitive IDmax may be ascribed to the undamaged two-dimensional hole gas channel. The interface state density (Dit) is evaluated to be 1.93 × 1012 cm−2·eV−1, and the relatively low value may be attributed to the uncontaminated interface in gate material. This work provides a promising strategy to realize normally-off H-terminated diamond FET for fail-safety and energy-efficient power electronic devices.

Single-step low-temperature synthesis routes for (Ba, Ce, Gd) hexaborides and their thermionic emission properties

Rare-earth/alkaline-earth hexaborides with high chemical stability and low work function have recently attracted much interest as promising thermionic cathodes. Their synthesis at low temperatures without post-synthesis purification treatments is still a significant challenge. The present work demonstrates a simple synthesis technique to produce pure barium, cerium and gadolinium hexaborides (BaB6, CeB6, and GdB6). For each hexaboride, a batch of samples was created by first milling highly pure precursor powders and then firing at various temperatures in a low-vacuum furnace. The synthesised products were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS). Their thermionic properties were investigated utilising a Schottky device. Pure BaB6, CeB6, and GdB6 were successfully synthesised at lower temperatures (≤1400 °C). Nanocrystalline CeB6 was found to be produced at the lowest temperature of 1200 °C. The mean particle size of pure CeB6 and GdB6 synthesised is seen to be in the sub-micron range, with the exception of large BaB6 particles. The estimated work functions of the BaB6, CeB6, and GdB6 cathodes are 1.61 ± 0.18 eV, 2.50 ± 0.09 eV, and 2.42 ± 0.09 eV, respectively. These findings imply that hexaborides, as promising thermionic emitters, can be easily produced at low temperatures.

Weyl semimetal in the rare-earth hexaboride family supporting a pseudonodal surface and a giant anomalous Hall effect

Rare-earth hexaborides offer a rich tapestry for exploring the interplay of topological orders, magnetism, and electron-correlation effects associated with protected quantum phenomena. Here, using first-principles modeling, we identify in cerium hexaboride ($\mathrm{Ce}{\mathrm{B}}_{6}$) a topological state that harbors a pseudonodal surface (PNS) along with double-Weyl fermions. An analysis of the electronic states in the vicinity of the Fermi level reveals the presence of ${M}_{z}$-mirror-symmetry-protected band crossings that involve itinerant ($d$) and localized ($f$) states of Ce. These band crossings are found to remain nearly gapless as one goes away from the mirror plane, driving the formation of PNS states. We also demonstrate the presence of coexisting double-Weyl fermions with chiral charges of $\ifmmode\pm\else\textpm\fi{}2$ on the ${C}_{4z}$ rotational axis. By analyzing the Berry curvature field associated with the topological states, we predict that $\mathrm{Ce}{\mathrm{B}}_{6}$ supports a giant anomalous Hall conductivity of $\ensuremath{-}1840 {\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}{\text{cm}}^{\ensuremath{-}1}$ in the slightly electron-doped regime, which would be larger than the values reported to date in magnetic Weyl semimetals. Our study thus indicates that $\mathrm{Ce}{\mathrm{B}}_{6}$, which combines ferromagnetic order with topological physics in a heavy-fermion matrix, would provide a promising playground for investigating topological magnetic states with giant anomalous Hall responses.

Novel Approach for the Synthesis of Highly Corrosion Resistant and Electrically Conductive Cerium Hexaboride Coating

Novel Approach for the Synthesis of Highly Corrosion Resistant and Electrically Conductive Cerium Hexaboride Coating

Electrochemical Behaviors and Thermodynamic Properties of Ce on Liquid Bi, Sn, and Zn Electrodes in Molten LiCl-KCl Salt

This study presents the electrochemical behaviors and thermodynamic properties of Ce on liquid Bi, Sn, and Zn electrodes in molten LiCl-KCl eutectic salt. First, the Ce-metal binary systems on the solid tungsten electrode were investigated to determine the formation of Ce-metal intermetallic compounds during the electrowinning process. In these experiments, the formation of five Ce–Bi intermetallic compounds, eight Ce–Sn intermetallic compounds, and nine Ce–Zn intermetallic compounds was confirmed from the oxidation peaks of cyclic voltammetry. The standard Gibbs free energy of formation of each intermetallic compound was calculated from plateaus of the open-circuit chronopotentiometry. Subsequently, the electrochemical behaviors of Ce were investigated on liquid Bi, Sn, and Zn electrodes using cyclic voltammetry. In particular, while the reduction potentials of Li and Ce were too close to differentiate on the liquid Bi and Sn electrodes, they were not on the liquid Zn electrode. Peak potentials from cyclic voltammetry were utilized to calculate the activity coefficients of Ce in the liquid Bi, Sn, and Zn electrodes, which were 3.16 × 10−14, 1.82 × 10−12, and 9.05 × 10−10, respectively.

Preparations of lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6)

AbstractDue 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.

Local origin of the strong field-space anisotropy in the magnetic phase diagrams of Ce1−xLaxB6 measured in a rotating magnetic field

Cubic f-electron compounds commonly exhibit highly anisotropic magnetic phase diagrams consisting of multiple long-range ordered phases. Field-driven metamagnetic transitions between them may depend not only on the magnitude, but also on the direction of the applied magnetic field. Examples of such behavior are plentiful among rare-earth borides, such as RB$_6$ or RB$_{12}$ ($R$ = rare earth). In this work, for example, we use torque magnetometry to measure anisotropic field-angular phase diagrams of La-doped cerium hexaborides, Ce$_{1-x}$La$_x$B$_6$ ($x$ = 0, 0.18, 0.28, 0.5). One expects that field-directional anisotropy of phase transitions must be impossible to understand without knowing the magnetic structures of the corresponding competing phases and being able to evaluate their precise thermodynamic energy balance. However, this task is usually beyond the reach of available theoretical approaches, because the ordered phases can be noncollinear, possess large magnetic unit cells, involve higher-order multipoles of 4f ions rather than simple dipoles, or just lack sufficient microscopic characterization. Here we demonstrate that the anisotropy under field rotation can be qualitatively understood on a much more basic level of theory, just by considering the crystal-electric-field scheme of a pair of rare-earth ions in the lattice, coupled by a single nearest-neighbor exchange interaction. Transitions between different crystal-field ground states, calculated using this minimal model for the parent compound CeB6, possess field-directional anisotropy that strikingly resembles the experimental phase diagrams. This implies that the anisotropy of phase transitions is of local origin and is easier to describe than the ordered phases themselves.

Stabilization of cold-field-emission current from a CeB6 single-crystal emitter by using a faceted (100) plane

A cerium hexaboride (CeB6) single crystal grown by the floating-zone method has a low work function of about 2.6 eV, and along with lanthanum hexaboride (LaB6), it is one of the most popular cathode materials. It has been widely used as the thermionic emitter of electron microscopes, such as SEMs and TEMs. However, cold-field emitters (CFEs) based on CeB6 and LaB6 have not been put to practical use due to their insufficient emission stability compared to that of conventional tungsten (W)-CFEs. In consideration of that background, in the present study, the stability of the emission current from a CeB6 single-crystal CFE was improved by using the (100) plane at the faceted tip of the single crystal. The CeB6⟨100⟩ single crystal was processed by electrochemical etching and successive high-temperature field evaporation and faceting under an appropriate electric field to make a (100) plane at the apex of the crystal. The improved CeB6(100)-CFE emitted a monochromatic electron beam, which has about three-quarters of the energy width of that of W(310)-CFEs. Emission current from the (100) plane maintained low emission noise, and emission decay in the electron-gun chamber of the SEM was suppressed. The resulting current noise is low enough to produce SEM images without image deterioration, and the relatively small decay makes it possible to use the CeB6(100) emitter for one flashing process per day.

Monochromatic electron emission from CeB6 (310) cold field emitter

Observation at low voltage using scanning electron microscopes (SEMs) enables the characterization of surface details on specimens on a nanometer scale and is widely used in science and industry. However, the energy width of the electron source restricts the spatial resolution of SEMs at low voltage, but it can be narrowed by lowering the work function of the emitter material. Here, we developed a cold field emitter using a cerium hexaboride single crystal (CeB6-CFE) as a monochromatic electron source. The work function of the CeB6 (310) plane was estimated to be as low as 2.25 ± 0.17 eV, and the energy width ranged from 0.17 to 0.26 eV for angular current densities ranging from 0.10 to 80 μA/sr. This energy width was 20% to 30% narrower than that of conventional W(310)-CFEs. Using the CeB6-CFE, the spatial resolution of the SEM at an acceleration voltage of 0.5 kV was improved by 11% compared with that of an SEM using the W(310)-CFE.

Regulated microarchitecture, spin polarization state, and observed charge transfers for cerium boride CeB6 under electrical Field

The thermal stabilities, microarchitectures as well as the electronic states of the cubic CeB6 under electrical field have been systematically investigated in detail within the framework of plane wave pseudo-potential density functional theory calculational method. Specifically, theCeB6 under electrical field of 0.0002 V/Å has lower total energy and enthalpy of formation. The cell of theCeB6 under electrical field is slightly expanded and the lattice expansion is isotropic, along with microarchitecture regulations. The distances between B are 2.523 Å, 1.707 Å and 1.784 Å, showing covalent bonds. There are 5 sub-bands for CeB6, the energy widths of bands are regulated with the conduction band and the first valence band moving downwards under electrical field. There are 3 band valleys and 5 band peaks for the CeB6, with metallic transition and decreased band gaps under electrical field. The middle conduction band and the first valence band are formed by f, d and p orbital electrons, respectively. The Ce s and the B orbital electrons tend to polarize under electrical field. The Ce f, Ce s and B orbital electrons are responsible for the ferrimagnetic magnetism under electrical field. There are charge transfers among these orbitals for CeB6 under electrical field.

Heavy Fermion Metal CeB6 in SubTHz and THz Range: The Electron Spin Resonance and Neutron Scattering Studies

Cerium hexaboride attracts attention of solid-state community for almost 50 years. Nowadays, this material is considered as a unique example of a system with orbital ordering resulting in formation of low-temperature magnetic phase with quadrupolar order, the so-called antiferroquadrupole phase. In crystal electric field 4f 1 state of Ce3+ splits into Γ7 doublet and Γ8 quartet, the latter is believed to be the ground state, as long as just Γ8 allows quadrupolar effects. An additional tool for studying rich physics of CeB6 appeared since the discovery in this material the ESR, which is specific to antiferroquadrupole (AFQ) phase and is missing in the paramagnetic phase. In the present review, we have brought together electron spin resonance and inelastic neutron scattering data, which allowed obtaining most detailed structure of the magnetic resonance modes in the AFQ phase in a wide-frequency range up to 0.6 THz. It is shown that apart paramagnetic resonance main mode with homogeneous precession of the magnetization, there are antiferromagnetic resonance modes as well, some of them existing in the AFQ phase. Analysis of the g factors demonstrates that available theories based on Γ8 ground state are facing difficulties with accounting experimental data, thus providing a challenge for developing of a theory correctly describing dynamic magnetic properties of this interesting material.

Effects of pressure on electronic structure and magnetic properties of cerium boride CeB6 cathode crystalline material

The thermal stabilities, electronic structures, magnetic properties and the charge transfers of the rare earth Cerium hexaborides CeB6 under isostatic pressure of 0 GPa and 1 GPa are systematically investigated in detail within the framework of density functional theory method with pseudopotential approximation. The analyzing results show that the Cerium Boride CeB6 under 1 GPa has relatively lower total energy of −1526.1675 eV than that of Cerium Boride CeB6 under 0 GPa. The Cerium Boride CeB6 under 1 GPa has band gap of 1.305 eV, which is 0.152 eV lower than that of the Cerium Boride CeB6 under 0 GPa of 1.457 eV. The work function of electrons is also decreased by 0.465 eV. There are three energy valleys in the bottom conduction band and four energy peaks in the top valance band, the emission efficiency should be high. The quantity of electrons that are readily to be motivated for emission is larger for Cerium hexaborides CeB6 under 1 GPa. The total partial density of states for Cerium Boride CeB6 under different isostatic pressure is mainly formed by B p electrons. The B should play more important role in electron emission for CeB6 under 1 GPa. The CeB6 under different isostatic pressure is ferromagnetic material. The combination bond effect between B is enhanced for Cerium Boride CeB6 under 1 GPa.

High-Efficiency Thermoelectric Single-Photon Detector Based on Lanthanum and Cerium Hexaborides

A design for a high-efficiency single-photon detector based on lanthanum and cerium hexaborides, which operates from the infrared to ultraviolet spectral ranges, is suggested. The results of computer simulations of heat transfer in the sensitive element of the detector upon the absorption of photons with energies of 0.5–4.13 eV are presented. To attain a high efficiency of the system of photon detection in the wavelength range from near infrared to ultraviolet, lanthanum hexaboride is proposed as the absorber and heat-sink material in the sensitive element. It is shown that a sensitive element of both single- and three-layer design made entirely of hexaborides will possess a gigahertz counting rate and a detection efficiency exceeding 90%.

Mechanical properties and microstructure evolution of pressureless-sintered B4C–SiC ceramic composite with CeO2 additive

Abstract Boron carbide ceramic composites (B 4 C)-silicon carbide (SiC) with the cerium oxide (CeO 2 ) additive, which was varied from 0 wt% to 9 wt%, were prepared by pressureless sintering at 2150 °C for 60 min. The effect of CeO 2 additive content on the microstructure and mechanical properties of the B 4 C–SiC ceramic composites was investigated in detail. In-situ synthesised cerium hexaboride (CeB 6 ) was identified in the B 4 C–SiC ceramic composites. B-rich transition zones (such as B 38.22 C 6 , B 51.02 C 1.82 ) were formed between the B 4 C and CeB 6 grains, which introduced local lattice distortion to increase the sintering driving force. The thermal conductivity coefficient of CeB 6 was higher than that of B 4 C, which benefited the delivery of heat quantity and helped achieve a highly dense and uniform sintered body. When the CeO 2 additive was excessively increased (more than 5 wt%), the CeB 6 grains had a large grain size and exhibited an increase in the amount of generated carbon monoxide (CO) gas, which led to an increase in the porosity of the B 4 C–SiC ceramic composites and decrease in the mechanical properties. The optimum values of the relative density, Vickers hardness, flexural strength, and fracture toughness of the B 4 C–SiC ceramic composite with 5 wt% CeO 2 additive were 96.42%, 32.21 GPa, 380 MPa, and 4.32 MPa m 1/2 , respectively.

Geochemical and pathfinder elements assessment in some mineralised regolith profiles in Bole-Nangodi gold belt in north-eastern Ghana

This study presents gold mineralisation and pathfinder elements characteristics in five surficial regolith profiles, with the aim of enhancing exploration strategies in the north-eastern Bole-Nangodi Gold Belt in Ghana. Samples were collected from mature soils and bedrocks in exploration pits and prepared for chemical and soil particle size analysis. 13 major elements, mineral forms and fifty-one trace elements were analysed using XRF, XRD and ICP-MS devices, respectively. SiO2, Fe2O3–MnO and Al2O3 are elevated in the A, B and C horizons, respectively, while Na2O–K2O–MgO–CaO–P2O5 systems dominate the bedrocks. Gold pathfinder element suites of As–Mo–Ag–Sn–Sb–Te–W–Hg–Bi are above Primitive Mantle values by a factor of > 5, while the mean chemical index of alteration (CIA) values are above 80%. Profiles contain > 70% quartz with stable mineral concentrations of 53, 18 and 29% in the A, B and C, horizons, respectively. The B horizon is the most altered horizon based on CIA, loss on ignition and Fe/Al ratios; the horizon accounts for 52% of the material and 76% of elements in the > 2 mm particle size. Mass balance and principal component analysis shows that Au exploration targets and the associated pathfinder element suites are the following: (1) horizon A with Sr–Ca–Ge–Sn–Th in the amphibolite and biotite gneiss profiles (2) horizons A and B with S–K–Zr–Tl–Ge in the volcaniclastic and (3) the bedrocks with Cu–Pb–Sb–Ag–Mo and Mn–Cr–Ba–V–Ce–Bi–Fe–Co–Sb–As–Se of the metavolcanic and phyllite profiles, respectively. The regolith models summarise the mineralogical and structural framework of the profiles and may largely influence exploration designs.

Identification of the impurity phase in high-purity CeB6 by convergent-beam electron diffraction.

The rare earth hexaborides are known for their tendency towards very high crystal perfection. They can be grown into large single crystals of very high purity by inert gas arc floating zone refinement. The authors have found that single-crystal cerium hexaboride grown in this manner contains a significant number of inclusions of an impurity phase that interrupts the otherwise single crystallinity of this prominent cathode material. An iterative approach is used to unequivocally determine the space group and the lattice parameters of the impurity phase based on geometries of convergent-beam electron diffraction (CBED) patterns and the symmetry elements that they possess in their intensity distributions. It is found that the impurity phase has a tetragonal unit cell with space group P4/mbm and lattice parameters a = b = 7.23±0.03 and c = 4.09±0.02 Å. These agree very well with those of a known material, CeB4. Confirmation that this is indeed the identity of the impurity phase is provided by quantitative CBED (QCBED) where the very close match between experimental and calculated CBED patterns has confirmed the atomic structure. Further confirmation is provided by a density functional theory calculation and also by high-angle annular dark-field scanning transmission electron microscopy.