The high-pressure magnetic properties of the heavy lanthanide elements Gd, Tb, Dy, Ho, Er, and Tm have been investigated using ac-magnetic susceptibility with a diamond anvil cell. It is found that the magnetic transition temperatures monotonically decrease with increasing pressure. In addition, the amplitudes of the magnetic transition signals decrease with increasing pressure, with the signals all eventually disappearing at pressures of $20\mathrm{GPa}$. In contrast to previous studies, we see no evidence of any pressure-induced transitions from one magnetically ordered phase to another in Gd, Tb, Dy, or Ho. The transition temperatures $T_{\mathit{crit}}$ are all found to drop at a rate proportional to their de Gennes factor, and the values of $T_{\mathit{crit}}∕T_{\mathit{crit}}(P=0)$ vs $P∕P_{\mathit{crit}}$, where $P_{\mathit{crit}}$ is the pressure at which the magnetic transition disappears, all sit on a single phase diagram.

High-pressure electrical conductivity experiments have been performed on the Mott insulator $\mathrm{MnO}$ to a maximum pressure of $106\mathrm{GPa}$. We observe a steady decrease in resistivity to $90\mathrm{GPa}$, followed by a large, rapid decrease by a factor of ${10}^5$ between 90 and $106\mathrm{GPa}$. Temperature cycling the sample at 87 and $106\mathrm{GPa}$ shows insulating and metallic behavior at these pressures, respectively. Our observations provide strong evidence for a pressure-induced insulator-to-metal transition beginning at $90\mathrm{GPa}$.

Superhard boron-rich boron carbide coatings were deposited on silicon substrates by microwave plasma chemical vapor deposition (MPCVD) under controlled conditions, which led to either a disordered or crystalline structure, as measured by X-ray diffraction. The control of either disordered or crystalline structures was achieved solely by the choice of the sample being placed either directly on top of the sample holder or within an inset of the sample holder, respectively. The carbon content in the B-C bonded disordered and crystalline coatings was 6.1 at.% and 4.5 at.%, respectively, as measured by X-ray photoelectron spectroscopy. X-ray diffraction analysis of the crystalline coating provided a good match with a B₅₀C₂-type structure in which two carbon atoms replaced boron in the α-tetragonal B₅₂ structure, or in which the carbon atoms occupied different interstitial sites. Density functional theory predictions were used to evaluate the dynamical stability of the potential B₅₀C₂ structural forms and were consistent with the measurements. The measured nanoindentation hardness of the coatings was as high as 64 GPa, well above the 40 GPa threshold for superhardness.

A novel approach is demonstrated for the synthesis of the high entropy transition metal boride (Ta, Mo, Hf, Zr, Ti)B₂ using a single heating step enabled by microwave-induced plasma. The argon-rich plasma allows rapid boro-carbothermal reduction of a consolidated powder mixture containing the five metal oxides, blended with graphite and boron carbide (B₄C) as reducing agents. For plasma exposure as low as 1800 °C for 1 h, a single-phase hexagonal AlB₂-type structure forms, with an average particle size of 165 nm and with uniform distribution of the five metal cations in the microstructure. In contrast to primarily convection-based (e.g., vacuum furnace) methods that typically require a thermal reduction step followed by conversion to the single high-entropy phase at elevated temperature, the microwave approach enables rapid heating rates and reduced processing time in a single heating step. The high-entropy phase purity improves significantly with the increasing of the ball milling time of the oxide precursors from two to eight hours. However, further improvement in phase purity was not observed as a result of increasing the microwave processing temperature from 1800 to 2000 °C (for fixed ball milling time). The benefits of microwave plasma heating, in terms of allowing the combination of boro-carbothermal reduction and high entropy single-phase formation in a single heating step, are expected to accelerate progress in the field of high entropy ceramic materials.

Atmospheric pressure plasma jet (APPJ) based modification as a facile method to modify the intimal surface of small caliber nanofibrous tubular tissue scaffolds for potential use as vascular-graft or spinal-cord conduit is reported here. Polycaprolactone, a biomaterial used in the US Food and Drug Administration approved scaffolds for various tissue regeneration and bioabsorbable suture applications, was electrospun into thin nano/microfibers to form seamless three-dimensional (3D) conduits of 4 mm intimal diameter. The 3D conduits were subjected to treatment with an APPJ produced by dielectric barrier discharge using controlled gas flow into ambient atmosphere. He/air or He/air/NH3 gas mixtures combined with 8.5 kV pulsed direct current signal proved effective in creating a sustained and reactive cold plasma jet to modify the intimal surface of tubular scaffolds without affecting its biomechanical properties. The treatment resulted in surface chemistry modification as indicated by enrichment of oxygenated functional groups. Surface chemistry was determined via x-ray photoelectron spectroscopy. Scanning electron microscopy and glycerol contact angle measurements were used to determine the surface morphology and surface wettability. The data support the conclusion that APPJ is as an effective, facile, and robust approach to modify the intimal surface of small-caliber (<4 mm) tubular conduits (successfully accomplished and initially reported here) for potential applications in vascular and neural tissue engineering.