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[en] One of the important challenges to the semiconductor industry today is to enhance the solid solubility of several dopants, boron in particular, in silicon. We calculate the equilibrium solid solubility of boron in Si from first principles and examine the effect of biaxial stress. We find an unexpectedly large enhancement, on the order of 150 percent, for only 1 percent strain primarily due to the charge of the substitutional boron impurity in Si. We point out that this effect is an intrinsic property of Si and is expected to be important for other dopants as well
[en] In order to improve the electrochemical performances of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy, a trace of boron was added in La2Mg(Ni0.85Co0.15)9 and rapid quenching techniques were used. La2Mg(Ni0.85Co0.15)9 B x (x = 0, 0.05, 0.1, 0.15, 0.2) hydrogen storage alloys were prepared by casting and rapid quenching. The microstructures and electrochemical performances of the as-cast and quenched alloys were determined and measured. The effects of the boron content and the quenching rate on the microstructures and electrochemical performances of the alloys were investigated in detail. The obtained results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni3 phase (PuNi3 structure), the LaNi5 phase and the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing boron. The Ni2B phase in the alloys containing boron nearly disappears after rapid quenching and the relative amount of each phase in the alloys changes with the variety of the quenching rate. The addition of boron obviously enhances the cycle stability of the as-cast and quenched alloys. The effects of boron content on the capacities of the as-cast and quenched alloys are different. The capacities of the as-cast alloys monotonously decrease with the increase of boron content, whereas the capacities of the as-quenched alloys have a maximum value with the change of boron content. The as-cast and quenched alloys have an excellent activation performance
[en] The geometrical structures and electronic properties of six fullerene isomers of C100 were studied at the HF/6-31G* and B3LYP/6-31G* levels, respectively. The results of the fully optimized calculations show that three C100 isomers 449:D2, 425:C1 and 442:C2 are near isoenergetic isomers. The energies and properties of C100 hexaanions were calculated. The C1006- (450:D5) isomer is predicted to be the most stable isomer at the B3LYP/6-31G* level, and the C1006- (449:D2) isomer is 44.1 kcal/mol higher in energy. The heterofullerenes C96X4 (X=N, P, B, Si) formed from the initial C100 (449:D2) have also been investigated at the B3LYP/6-31G* level. The HOMO-LUMO gaps and aromaticities show that the replacement of fullerene carbon atoms with four heteroatoms can enhance the electronic stabilization of C100 (449:D2).
[en] In this work, microstructure characteristics of α phase in Ti‐40Al‐8Nb‐0.5B alloys (at%) after deformation in the β and (β+α) phase regions are examined. The experimental results indicate that the microstructure characteristics of the α phase are considerably affected by the deformation temperature. During the deformation in the β phase area, the β phase is not only elongated perpendicular to the compression direction, but also presents a〈100〉‐〈111〉double fiber texture. After the β→α transformation, a part of the α phase exhibits an equiaxed morphology and the others show lath‐like shapes. Due to the microstructural heredity, the α phase of the sample deformed in the β phase field presents a〈11‐20〉‐〈10‐10〉double fiber texture. In contrast, refined α phase with randomly distributed orientation is produced after the deformation in the (β+α) phase field and this is caused by the dynamic recrystallization during the deformation process. (© 2020 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
[en] Multi-element doping of graphene could potentially provide functionalities that are not available in the single-element doping approach, but it has not been actively studied so far. Carrying out first-principles calculations, we study the structural, electronic, and transport properties of B–P edge-co-doped armchair graphene nanoribbons (aGNRs). We find that the B, P-complex edge-doped aGNRs exhibit an n-type transport behavior, which is counterintuitive considering the p-type and bipolar characters of the corresponding B- and P-doped aGNRs, respectively. Moreover, we show that the n-type property of B, P co-doped aGNRs is superior to that of representative N-doped aGNRs in terms of preserving the valence band edge conductance spectrum. Analyzing the mechanisms, we demonstrate that the structural distortion rather than chemical valence induces the anomalous donor character of B, P co-doped aGNRs. We thus propose a systematic modification of GNR atomic structures via co-doping as a novel approach to control charge transport characteristics of GNRs. (letter)
[en] Boron addition to Ni53.5Mn26.0Ga20.5 alloy is found to modify the microstructure and mechanical properties substantially. Studies on (Ni53.5Mn26.0Ga20.5)Bx alloys reveal that boron addition causes grain refinement which led to an increase in compressive strength in x=0.5 alloy which also retained multimode twinning. Substantial second phase segregation rich in Ni was seen at grain boundaries, the extent of which increased with boron content. This led to a compositional shift in the matrix phase which resulted in a reduction in the martensitic transformation temperature and which in turn caused an easy deformation at low stresses and suppression of multimode twinning in x=1.0 alloy
[en] Intense terahertz (THz) stimulated emission from boron-doped SiGe/Si quantum well structures with internal strain has been observed recently. We present a theoretical calculation which shows the formation of resonant states, and explains the origin of the observed temperature dependence of the dc conductivity under low bias voltage. Thus, the mechanism of THz lasing is population inversion of the resonant state with respect to the localized impurity states. This is the same mechanism of lasing as in uniaxially stressed p-Ge THz lasers. Copyright 2001 American Institute of Physics
[en] Inoculation has been studied in the semi-solid-metal (SSM) casting by sole boron addition. By boron addition, the structure is not only refined but also the sphericity of the primary α-Al particles increased. Higher globularity coupled with smaller primary particles leads to superior flow of the billet in the compression test. It is also shown that the dissolved boron in the matrix of the master alloy and AlB2 particles are the key parameters in this evolution
[en] Melt spun ribbons of a series of SmFe_1_2B_x (x=0.0, 0.5, 0.75, 1.0, 1.25, and 1.5) have been prepared by the melt spinning technique. Sm–Fe–B melt spun ribbons with single phase TbCu_7-type structure were prepared from the SmFe_1_2B_x (x=0.5, 0.75, and 1.0) alloys at the surface velocity around 40 m/s. The addition of boron not only inhibits the appearance of soft magnetic phase α-Fe, but also enhances the ability of amorphous formation for melt spun Sm–Fe ribbons. The concentration of boron atoms, however, exceeds the limit of the solubility (x>1.0) of Sm–Fe alloys, which does not impede the appearance of α-Fe but accelerates the formation of metastable phase Sm_2Fe_2_3B_3 that is unfavorable to their magnetic properties. Moreover, it is found that the addition of boron whose concentration is 0.0≤x≤0.75 can stabilize the metastable TbCu_7-type structure because of the increase of the lattice parameter ratio c/a. The magnetic properties of as-annealed SmFe_1_2B_1_._0 melt spun ribbons with an energy product of 2.19MGOe, a coercivity of 2.36 kOe and a remanence of 4.8 kGs have been achieved. The microstructural characteristics of as-annealed melt spun SmFe_1_2 and SmFe_1_2B_1_._0 ribbons have been discussed as well. The following sequence of the hyperfine field H(6l)< H(3g)< H(2e) and the isomer shift δ(3g)<δ(6l)<δ(2e) is obtained by the analysis of "5"7Fe Mossbauer spectra. As the boron content is added gradually, the hyperfine fields of 3g and 6l sites increase slightly due to the competition of the positive electron polarization and the negative polarization. However, the value of H(2e) is almost constant. - Highlights: • A certain amount of boron additions can inhibit the emergence of the soft magnetic phase α-Fe and improve the ability of amorphous formation. • There is a solubility limit of boron atom within melt spun Sm–Fe alloys with TbCu_7-type structure, and the metastable phase Sm_2Fe_2_3B_3 will appear when the content of boron exceeds the limit. • The boron additions greatly refine the grain size of SmFe_1_2B_1_._0ribbons at the surface velocity about 40 m/s, the mean grain size of about 22 nm. • The following sequence of the hyperfine field H(6l)< H(3g)< H(2e) and the isomer shift δ(3g)<δ(6l)<δ(2e) is obtained by the analysis of "5"7Fe Mossbauer spectra.