The well-documented formation of amorphous bands in boron carbide (B 4 C) under contact loading has been identified in the literature as one of the possible mechanisms for its catastrophic failure. To mitigate amorphization, Si-doping was suggested by an earlier computational work, which was further substantiated by an experimental study. However, there have been discrepancies between theoretical and experimental studies, about Si replacing atom/s in B 12 icosahedra or the C-B-C chain. Dense single phase Si-doped boron carbide is produced through a conventional scalable route. A powder mixture of SiB 6 , B 4 C, and amorphous boron is reactively sintered, yielding a dense Si-doped boron carbide material.A combined analysis of Rietveld refinement on XRD pattern coupled with electron density difference Fourier maps and DFT simulations were performed in order to investigate the location of Si atoms in boron carbide lattice. Si atoms occupy an interstitial position, between the icosahedra and the chain. These Si atoms are bonded to the chain end C atoms and result in a kinked chain. Additionally, these Si atoms are also bonded to the neighboring equatorial M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT2 B atom of the icosahedra, which is already bonded to the C atom of the chain, forming a bridge like geometry. Si atoms are found to reside around the chain, resulting in a kinked chain. These Si atoms lie close to boron atom of the neighboring icosahedra. Owing to this bonding, distance suggests weak bonding and Si is anticipated to stabilize the icosahedra through electron donation, which is expected to help in mitigating stress-induced amorphization. Possible supercell structures are suggested along with the most plausible structure for Si-doped boron carbide.

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We have studied the effect that structural defects and chemical impurities have on the electron mobility in GaN films grown in a production scale metalorganic chemical vapor depositon system. Structural defects such as dislocations, stacking faults, twins, and amorphous regions in the buffer layer have been examined. In general, we have found that the structural defects are not the primary contributor to low mobility. However, there is one type of defect Cnanopipe") that may be an important indirect contributor to mobility degradation by acting as a conduit into the film interior for impurities such as carbon and oxygen. We have also investigated the role that the principal impurities play in determining the electrical performance. Of particular concern was the presence of carbon resulting from an incomplete dissociation of trimethylgallium precursor gas. Also present in the films were traces of oxygen, hydrogen, and aluminum, while heavy metals such as iron, chromium, and molybdenum were detected at or near the resolution limit of secondary ion mass spectrometry analysis. We present evidence for compensation by carbon at low carrier concentrations, which would help to explain the anomalous mobility behavior in GaN.

The density, surface tension, and viscosity of the melts from the PbO‐B2O3‐SiO2 system have been measured at temperatures in the range 1073–1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ∼60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30–60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction.

Boron carbide suffers from a loss of strength and toughness when subjected to high shear stresses due to amorphization. Here, we report that a small amount of Si doping (~1 atomic %) leads to a substantial decrease in stress-induced amorphization due to a noticeable change of the deformation mechanisms in boron carbide. In the undoped boron carbide, the Berkovich indentation–induced quasi-plasticity is dominated by amorphization and microcracking along the amorphous shear bands. This mechanism resulted in long, distinct, and single-variant shear faults. In contrast, substantial fragmentation with limited amorphization was activated in the Si-doped boron carbide, manifested by the short, diffuse, and multivariant shear faults. Microcracking via fragmentation competed with and subsequently mitigated amorphization. This work highlights the important roles that solute atoms play on the structural stability of boron carbide and opens up new avenues to tune deformation mechanisms of ceramics via doping.