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Metal oxide thermal reduction, enabled by microwave-induced plasma, was used to synthesize high entropy borides (HEBs). This approach capitalized on the ability of a microwave (MW) plasma source to efficiently transfer thermal energy to drive chemical reactions in an argon-rich plasma. A predominantly single-phase hexagonal AlB2-type structural characteristic of HEBs was obtained by boro/carbothermal reduction as well as by borothermal reduction. We compare the microstructural, mechanical, and oxidation resistance properties using the two different thermal reduction approaches (i.e., with and without carbon as a reducing agent). The plasma-annealed HEB (Hf0.2, Zr0.2, Ti0.2, Ta0.2, Mo0.2)B2 made via boro/carbothermal reduction resulted in a higher measured hardness (38 ± 4 GPa) compared to the same HEB made via borothermal reduction (28 ± 3 GPa). These hardness values were consistent with the theoretical value of ~33 GPa obtained by first-principles simulations using special quasi-random structures. Sample cross-sections were evaluated to examine the effects of the plasma on structural, compositional, and mechanical homogeneity throughout the HEB thickness. MW-plasma-produced HEBs synthesized with carbon exhibit a reduced porosity, higher density, and higher average hardness when compared to HEBs made without carbon.

The design of metal nanoparticle-modified polymer surfaces in a green and scalable way is both desirable and highly challenging. Herein, a new green low-temperature plasma-based

We report high-pressure structural studies (52 GPa) at room temperature combined with magnetic [(M(T):1GPa] and electrical resistivity [(ρ(T):0-21GPa)] measurements down to 2 K on Fe0.99Ni0.01Se0.5Te0.5 superconductor using designer diamond anvils (D-DAC) pressure cell. The M(T) data show huge enhancement of superconducting transition temperature (Tc) from 8.62 to 14.8 K (1 GPa) and ρ(T) reveal maximum enhancement of Tc ~ 30.5 K at 3 GPa (dTc/dP = ~ 7.19 K/GPa) followed by moderate decrease of Tc up to 19 K at 7.5 GPa, and further increasing pressure Tc gets vanished at 10.6 GPa. The reduction of Tc due to the occurrence of structural transition that is likely associated with possible reduction of charge carriers in the density of states in Fermi surface. The high-pressure XRD measurement shows tetragonal phase exists up to 7 GPa, followed by mixed phase which is visible between 7.5 GPa and 14.5 GPa. The structural transformation occurs at 15 GPa from tetragonal (P4/nmm) to NiAs -type hexagonal phase (P63/mmc) and it is stable up to 52 GPa, confirmed from the equation of state (EOS) and it can be correlated with variation of Tc under pressure for Fe0.99Ni0.01Se0.5Te0.5 chalcogenide superconductors.

Thermoelastic behavior of transition metal boride Os2B3 was studied under quasi-hydrostatic and isothermal conditions in a Paris-Edinburgh cell to 5.4 GPa and 1273 K. In-situ Energy Dispersive X-ra...

Eu(Fe

We search for new superhard B-N-O compounds with an iterative machine learning (ML) procedure, where ML models are trained using sample crystal structures from evolutionary algorithm. We first use cohesive energy to evaluate the thermodynamic stability of varying B$_x$N$_y$O$_z$ compositions, and then gradually focus on compositional regions with high cohesive energy and high hardness. The results converge quickly after a few iterations. Our resulting ML models show that B$_{x+2}$N$_{x}$O$_{3}$ compounds with $x \geq 3$ (like B$_5$N$_3$O$_3$, B$_6$N$_4$O$_3$, etc.) are potentially superhard and thermodynamically favorable. Our meta-GGA density functional theory calculations indicate that these materials are also wide bandgap ($\ge 4.4$ eV) insulators, with the valence band maximum related to the $p$-orbitals of nitrogen atoms near vacant sites. This study demonstrates that an iterative method combining ML and ab initio simulations provides a powerful tool for discovering novel materials., Comment: 8 pages, 5 figures

The phase transitions and equation of state measurements were carried out on rare earth metal Holmium (Ho) to 282 GPa using toroidal diamond anvils thereby doubling the pressure range to which it h...

Density functional theory predictions have been combined with the microwave-plasma chemical vapor deposition technique to explore metastable synthesis of boron-rich boron-carbide materials. A thin film synthesis of high-hardness (up to 37 GPa) B50C2 via chemical vapor deposition was achieved. Characterization of the experimental crystal structure matches well with a new theoretical model structure, with carbon atoms inserted into the boron icosahedra and 2b sites in a α-tetragonal B52 base structure. Previously reported metallic B50C2 structures with carbons inserted only into the 2b or 4c sites are found to be dynamically unstable. The newly predicted structure is insulating and dynamically stable, with a computed hardness value and electrical properties in excellent agreement with the experiment. The present study thus validates the density functional theory calculations of stable crystal structures in boron-rich boron-carbide system and provides a pathway for large-area synthesis of novel materials by the chemical vapor deposition method.

With ${T}_{c}\ensuremath{\sim}9.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}, {\mathrm{Be}}_{22}\mathrm{Re}$ exhibits one of the highest critical temperatures among Be-rich compounds. We have carried out a series of high-pressure electrical resistivity measurements on this compound to 30 GPa. The data show that the critical temperature ${T}_{c}$ is suppressed gradually at a rate of $d{T}_{c}/dP=\ensuremath{-}0.05\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{GPa}$. Using density functional theory (DFT) calculations of the electronic and phonon density of states (DOS) and the measured critical temperature, we estimate that the rapid increase in lattice stiffening in ${\mathrm{Be}}_{22}\mathrm{Re}$ overwhelms a moderate increase in the electron-ion interaction with pressure, resulting in the decrease in ${T}_{c}$. High-pressure x-ray diffraction measurements show that the ambient pressure crystal structure of ${\mathrm{Be}}_{22}\mathrm{Re}$ persists to at least 154 GPa.

Shallow-water marine invertebrates living near the upper limits of their thermal tolerances are uniquely susceptible to climate warming. This is particularly the case for species that occur in geographic regions where larval dispersal or adult migration to cooler waters is not an option. This scenario aptly describes populations of the seagrass-associated sea urchin Lytechinus variegatus inhabiting the northern Gulf of Mexico where northward movement is restricted by a coastline. In the present study, we exposed juvenile L. variegatus to chronic ambient (26 °C) and predicted near-future (30 °C) temperature treatments for 90 days. X-ray Diffraction (XRD) was employed to determine the Mg/Ca ratios of the spines, test, and Aristotle's lantern of individuals sub-sampled at 30, 60, and 90 days. We found that while individuals grew at similar rates, Mg/Ca ratios in all skeletal components were overall significantly lower in individuals held at 30 °C than at 26 °C.

To establish the microscopic P-T phase diagram of recent 112-type iron-pnictides $\mathrm{Eu}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}){\mathrm{As}}_{2}$ (x = 0, 0.04), high-pressure synchrotron M\"ossbauer spectroscopy experiments in $^{151}\mathrm{Eu}$ and $^{57}\mathrm{Fe}$ have been performed. In ${\mathrm{EuFeAs}}_{2}$ application of pressure completely suppresses the itinerant electron magnetism from the Fe sublattice and the local-moment magnetism in Eu ions at $\ensuremath{\sim}10\phantom{\rule{0.16em}{0ex}}$ and $\ensuremath{\sim}11.6\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, respectively. High-pressure x-ray diffraction experiments in ${\mathrm{EuFeAs}}_{2}$ reveal an anomalous change in the lattice parameters and a discontinuity in volume around 10 GPa, suggesting an isostructural transition at this pressure. With Ni-doping (x = 0.04), a collapse of local magnetic order occurs at $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, a lower critical pressure compared with the parent compound. In both systems, the suppression of local-moment magnetism is associated with a significant increase of mean valence in Eu ions.

Dysprosium (Dy) has been studied using neutron diffraction under high pressures and low temperatures at a spallation neutron source by employing a large-volume diamond anvil cell. Companion measurements at different central wavelengths allow the collection over extended reciprocal space with momentum transfer Q covering the range from 0.5 A-1 to 5.5 A-1. Upon cooling to 15 K, magnetic ordering was observed in the hexagonal close-packed (hcp), alpha-samarium (α-Sm), and double hexagonal close packed (dhcp) phases of Dy to 22 GPa. We report on previously undetected magnetic superlattice reflections signaling antiferromagnetic transition for both the α-Sm and dhcp phases of Dy. Magnetic structure refinements for the α-Sm phase shows a complex phase comprising two magnetic propagation vectors k = (1/2, 1/2, 1/2) and k = (1/2, 0, 0). Magnetic structure refinements for the dhcp phase yield a single magnetic propagation vector k = (1/2, 0, 1/3) and a possible magnetic space group Pbnma. The refined magnetic structures are provided to the highest pressure of 22 GPa.

Native extracellular matrix (ECM) possesses the biochemical cues to promote cell survival. However, decellularized, the ECM loses its cell supporting mechanical integrity. We report, here, a novel biohybrid vascular graft of polycaprolactone (PCL), poliglecaprone (PGC) incorporated with human biomatrix as functional materials for vascular tissue interfacing by electrospinning, thus harnessing the biochemical cues from the ECM and the mechanical integrity of the polymer blends. The fabricated fibro-porous tubular small diameter graft (i.d. = 4 mm) from polymer blend was coated with a cocktail of collagenous matrix derived from human placenta called HuBiogel™. The compositional, morphological, and mechanical properties of graft were measured and compared with a non-coated tubular PCL/PGC graft using Fourier Transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). BCA assay was used to calculate the protein content and coating-uniformity throughout the hybrid graft. Mechanical properties such as tensile strength (1.6 MPa), Young's modulus (2.4 MPa), burst pressure (>1900 mmHg), and suture retention strength (2.3 N) of hybrid graft were found to be comparable to native blood vessels. Protein coating has improved the hydrophilicity and the biocompatibility (cell viability and cell-attachment) enhanced with human umbilical vein endothelial cells (HUVECs) seeded in vitro onto the lumen layer of the graft over two weeks. The overall results promise this new biohybrid graft to be a potential candidate for vascular tissue interface and regeneration.

The correlated electron material CePd$_2$P$_2$ crystallizes in the ThCr$_2$Si$_2$ structure and orders ferromagnetically at 29 K. Lai et al. [Phys. Rev. B 97, 224406 (2018)] found evidence for a ferromagnetic quantum critical point induced by chemical compression via substitution of Ni for Pd. However, disorder effects due to the chemical substitution interfere with a simple analysis of the possible critical behavior. In the present work, we examine the temperature - pressure - magnetic field phase diagram of single crystalline CePd$_2$P$_2$ to 25 GPa using a combination of resistivity, magnetic susceptibility, and x-ray diffraction measurements. We find that the ferromagnetism appears to be destroyed near 12 GPa, without any change in the crystal structure., Comment: 7 pages, 9 figures

High pressure study on ultra-hard transition-metal boride Os

We report a novel and facile organosilane plasma polymerization method designed to improve the surface characteristics of poly(tetrafluoroethylene) (PTFE). We hypothesized that the polymerized silane coating would provide an adhesive surface for endothelial cell proliferation due to a large number of surface hydroxyl groups, while the large polymer networks on the surface of PTFE would hinder platelet attachment. The plasma polymerized PTFE surfaces were then systematically characterized via different analytical techniques such as FTIR, XPS, XRD, Contact angle, and SEM. The key finding of the characterization is the time-dependent deposition of an organosilane layer on the surface of PTFE. This layer was found to provide favorable surface properties to PTFE such as a very high surface oxygen content, high hydrophilicity and improved surface mechanics. Additionally, in vitro cellular studies were conducted to determine the bio-interface properties of the plasma-treated and untreated PTFE. The important results of these experiments were rapid endothelial cell growth and decreased platelet attachment on the plasma-treated PTFE compared to untreated PTFE. Thus, this new surface modification technique could potentially address the current challenges associated with PTFE for blood contact applications, specifically poor endothelial cell growth and risk of thrombosis.

An emerging class of superhard materials for extreme environment applications are compounds formed by heavy transition metals with light elements. In this work, ultrahigh pressure experiments on transition metal rhenium diboride (ReB2) were carried out in a diamond anvil cell under isothermal and non-hydrostatic compression. Two independent high-pressure experiments were carried out on ReB2 for the first time up to a pressure of 241 GPa (volume compression V/V0 = 0.731 &plusmn, 0.004), with platinum as an internal pressure standard in X-ray diffraction studies. The hexagonal phase of ReB2 was stable under highest pressure, and the anisotropy between the a-axis and c-axis compression increases with pressure to 241 GPa. The measured equation of state (EOS) above the yield stress of ReB2 is well represented by the bulk modulus K0 = 364 GPa and its first pressure derivative K0&acute, = 3.53. Corresponding density-functional-theory (DFT) simulations of the EOS and elastic constants agreed well with the experimental data. DFT results indicated that ReB2 becomes more ductile with enhanced tendency towards metallic bonding under compression. The DFT results also showed strong crystal anisotropy up to the maximum pressure under study. The pressure-enhanced electron density distribution along the Re and B bond direction renders the material highly incompressible along the c-axis. Our study helps to establish the fundamental basis for anisotropic compression of ReB2 under ultrahigh pressures.

This study investigates the changes of magnetic ordering temperature via nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to such local lattice variations. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Neel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a 122 parent of iron arsenide superconductors, is found through synthesis to have ordering below TN = 195 K (for the disordered crystal) or TN = 175 K (for the ordered crystal). In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) A vs. 2.7745(3) A], a randomized in-plane defect structure, and diffuse scattering along the [00L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower TN crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger TN and a higher superconducting temperature (Tc) upon the application of pressure. First principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122., 4 main figures

Cerium-12at%Praseodymium(Ce0.88Pr0.12) and Ce-50at%Praseodymium(Ce0.50Pr0.50) alloy samples that contain a random solid-solution of Ce (4f1 (J = 5/2)) and Pr (4f2 (J = 4)) localized f-states have b...

We report a method to increase the efficiency of radio-frequency (RF) generated plasma for surface modification of electrospun biomaterials by introducing magnetization. The x-ray photoelectron spectroscopy (XPS) reveals the oxygen/carbon ratio is consistently higher for various exposure times for magnetized plasma than non-magnetized plasma. The principle demonstrated here supports the use of magnetic fields as an additional controllable parameter in plasma processing of biomaterials and is extendable to other plasma sources. The surface activation and functionalization of biomaterials has impact in the broader arena of tissue engineering applications in that magneto-plasma processing (MPP) enables us to tune the shape of plasma plume for selective enhanced functionalization of surface of scaffolds, which in turn has wide applications for basic cell-patterning science and in applied regenerative medicine.

The compression behavior of osmium metal was investigated up to 280 GPa (volume compression V/Vo = 0.725) under nonhydrostatic conditions at ambient temperature using angle dispersive axial x-ray diffraction (A-XRD) with a diamond anvil cell (DAC). In addition, shear strength of osmium was measured to 170 GPa using radial x-ray diffraction (R-XRD) technique in DAC. Both diffraction techniques in DAC employed platinum as an internal pressure standard. Density functional theory (DFT) calculations were also performed, and the computed lattice parameters and volumes under compression are in good agreement with the experiments. DFT predicts a monotonous increase in axial ratio (c/a) with pressure and the structural anomalies of less than 1% in (c/a) ratio reported below 150 GPa were not reproduced in theoretical calculations and hydrostatic measurements. The measured value of shear strength of osmium ( τ ) approaches a limiting value of 6 GPa above a pressure of 50 GPa in contrast to theoretical predictions of 24 GPa and is likely due to imperfections in polycrystalline samples. DFT calculations also enable the studies of shear and tensile deformations. The theoretical ideal shear stress is found along the (001)[1–10] shear direction with the maximal shear stress ∼24 GPa at critical strain ∼0.13.

Multi-angle energy-dispersive X-ray diffraction studies and white-beam X-ray radiography were conducted with a cylindrically shaped (1 mm diameter and 0.7 mm high) high-boron-content borosilicate glass sample (17.6% B2O3) to a pressure of 13.7 GPa using a Paris-Edinburgh (PE) press at Beamline 16-BM-B, HPCAT of the Advanced Photon Source. The measured structure factor S(q) to large q = 19 A−1 is used to determine information about the internuclear bond distances between various species of atoms within the glass sample. Sample pressure was determined with gold as a pressure standard. The sample height as measured by radiography showed an overall uniaxial compression of 22.5% at 13.7 GPa with 10.6% permanent compaction after decompression to ambient conditions. The reduced pair distribution function G(r) was extracted and Si–O, O–O and Si–Si bond distances were measured as a function of pressure. Raman spectroscopy of the pressure recovered sample as compared to starting material showed blue-shift a...

We report the observation of the pressure-induced, fully collapsed tetragonal phase of $\mathrm{CaRbF}{\mathrm{e}}_{4}\mathrm{A}{\mathrm{s}}_{4}$ for $P\ensuremath{\sim}22\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ via high-pressure x-ray diffraction and magnetotransport measurements. The x-ray measurements, along with resistivity measurements, show that there is an initial half-collapsed tetragonal phase for $6lPl22\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, in which superconductivity is continuously suppressed from ${T}_{\mathrm{c}}=35\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at $P=3.1\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ to ${T}_{\mathrm{c}}l2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for $P\ensuremath{\ge}17.2\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, as well as signs of the fully collapsed tetragonal phase near $P=22\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. Density functional calculations suggest that both of these transitions are driven by increased As-As bonding, first across the Ca layer, and then at the second transition, across the Rb layer. Although electrical resistivity measurements in the fully collapsed tetragonal phase do not show superconductivity, there is a change in the slope of both the Hall coefficient and the longitudinal resistance near 22 GPa, suggesting a strong correlation between the electronic and lattice degrees of freedom in this new iron-based superconductor.

Superhydrophobic surfaces have gained increased attention due to the high water-repellency and self-cleaning capabilities of these surfaces. In the present study, we explored a novel hybrid method of fabricating superhydrophobic poly(tetrafluoroethylene) (PTFE) surfaces by combining the physical etching capability of oxygen plasma with the plasma-induced polymerization of a organic monomer methyl methacrylate (MMA). This novel hybrid combination of oxygen-MMA plasma has resulted in the generation of superhydrophobic PTFE surfaces with contact angle of 154°. We hypothesized that the generation of superhydrophobicity may be attributed to the generation of fluorinated poly(methyl methacrylate) (PMMA) moieties formed by the combined effects of physical etching causing de-fluorination of PTFE and the subsequent plasma polymerization of MMA. The plasma treated PTFE surfaces were then systematically characterized via XPS, FTIR, XRD, DSC and SEM analyses. The results have clearly shown a synergistic effect of the oxygen/MMA combination in comparison with either the oxygen plasma alone or MMA vapors alone. Furthermore, the reported new hybrid combination of Oxygen-MMA plasma has been demonstrated to achieve superhydrophobicity at lower power and short time scales than previously reported methods in the literature. Hence the reported novel hybrid strategy of fabricating superhydrophobic PTFE surfaces could have futuristic potential towards biointerface applications.

ZrSiS has recently gained attention due to its unusual electronic properties: nearly perfect electron-hole compensation, large, anisotropic magneto-resistance, multiple Dirac nodes near the Fermi level, and an extremely large range of linear dispersion of up to 2 eV. We have carried out a series of high pressure electrical resistivity measurements on single crystals of ZrSiS. Shubnikov-de Haas measurements show two distinct oscillation frequencies. For the smaller orbit, we observe a change in the phase of 0.5, which occurs between 0.16 - 0.5 GPa. This change in phase is accompanied by an abrupt decrease of the cross-sectional area of this Fermi surface. We attribute this change in phase to a possible topological quantum phase transition. The phase of the larger orbit exhibits a Berry phase of pi and remains roughly constant up to 2.3 GPa. Resistivity measurements to higher pressures show no evidence for pressure-induced superconductivity to at least 20 GPa., Comment: 5 pages, 3 figures

For several decades, plasma processing has been employed in the areas of food processing, manufacturing, and agriculture. Plasma processing has also been recognized as greatly beneficial in the field of tissue engineering for the modification of biomaterials. Polyethylene terephthalate (PET) has been employed as a vascular graft material but fails in small diameter applications. In this work, a multifaceted approach combining electrospinning to produce nano- and microscale fibers from PET blended with polybutylene terephthalate (PBT) added for flexibility and plasma modification for enhancing the surface chemistry is demonstrated to be an efficient approach to increase the biocompatibility as evidenced by enhanced fibroblast growth. The analysis of the surface chemistry shows an increase in oxygenated surface functionality, while the bulk analysis shows no significant changes. Thus, an efficient methodology for producing PET/PBT-based grafts that are easily modified with low-temperature plasma and show enhanced biocompatibility for vascular tissue engineering applications is reported.

Shear strength measurements have been carried out on rhenium diboride, ReB2, to a pressure of 74 GPa using a Radial X-ray Diffraction (R-XRD) technique in a diamond anvil cell using platinum as an internal x-ray pressure standard. The R-XRD result has provided a unique insight into the deformation of hexagonal crystal lattice under non-hydrostatic compression and variation of shear strength with increasing pressure. From R-XRD data, we have estimated hydrostatic component of compression to determine an equation of state of rhenium diboride yielding a bulk modulus of K0 = 366 ± 25 GPa with a pressure derivative K 0 ′ = 4.3 ± 0.5 in good agreement with hydrostatic density functional theory calculations. The average lower bound of shear strength (τ) from various diffraction planes was then calculated using the measured interplanar d-spacing (dm) and hydrostatic component of d-spacing (dp) to be shown to approach 6.7 ± 0.4 GPa at 70 GPa. Our results show that the anisotropic compression effects observed in ReB2 under hydrostatic compression are correlated to electronic structure changes under compression as predicted by theoretical calculations.