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Non-hydrostatic high pressure X-ray diffraction is used to study the hardness of superhard ReB ₂ nanocrystals. All nanocrystals show less plastic deformation under load than bulk ReB ₂ , with the smallest nanocrystals showing the most enhancement.

Rhenium diboride (ReB₂) exhibits high differential strain due to its puckered boron sheets that impede shear deformation. Here, we demonstrate the use of solid solution formation to enhance the Vickers hardness and differential strain of ReB₂. ReB₂-structured solid solutions (Re_0.98Os_0.02B₂ and Re_0.98Ru_0.02B₂, noted as “ReOsB₂” and “ReRuB₂”) were synthesized via arc-melting from the pure elements. In-situ high-pressure radial x-ray diffraction was performed in the diamond anvil cell to study the incompressibility and lattice strain of ReOsB₂ and ReRuB₂ up to ~56 GPa. Both solid solutions exhibit higher incompressibility and differential strain than pure ReB₂. However, while all lattice planes aremore » strengthened by doping osmium (Os) into the ReB₂ structure, only the weakest ReB₂ lattice plane is enhanced with ruthenium (Ru). These results are in agreement with the Vickers hardness measurements of the two systems, where higher hardness was observed in ReOsB₂. The combination of high-pressure studies with experimentally observed hardness data provides lattice specific information about the strengthening mechanisms behind the intrinsic hardness enhancement of the ReB₂ system.« less

High pressure represents extreme environments and provides opportunities for materials discovery. Thermal transport under high hydrostatic pressure has been investigated for more than 100 years and all measurements of crystals so far have indicated a monotonically increasing lattice thermal conductivity. Here we report in situ thermal transport measurements in the newly discovered semiconductor crystal boron arsenide, and observe an anomalous pressure dependence of the thermal conductivity. We use ultrafast optics, Raman spectroscopy and inelastic X-ray scattering measurements to examine the phonon bandstructure evolution of the optical and acoustic branches, as well as thermal conductivity under varied temperatures and pressures upmore » to 32 gigapascals. Using atomistic theory, we attribute the anomalous high-pressure behaviour to competitive heat conduction channels from interactive high-order anharmonicity physics inherent to the unique phonon bandstructure. Our study verifies ab initio theory calculations and we show that the phonon dynamics—resulting from competing three-phonon and four-phonon scattering processes—are beyond those expected from classical models and seen in common materials. In conclusion, this work uses high-pressure spectroscopy combined with atomistic theory as a powerful approach to probe complex phonon physics and provide fundamental insights for understanding microscopic energy transport in materials of extreme properties.« less

We report the formation of an ultrahigh CO₂-loaded pure-SiO₂ silicalite-1 structure at high pressure (0.7 GPa) from the interaction of empty zeolite and fluid CO₂ medium. The CO₂-filled structure was characterized in situ by means of synchrotron powder X-ray diffraction. Rietveld refinements and Fourier recycling allowed the location of 16 guest carbon dioxide molecules per unit cell within the straight and sinusoidal channels of the porous framework to be analyzed. The complete filling of pores by CO₂ molecules favors structural stability under compression, avoiding pressure-induced amorphization below 20 GPa, and significantly reduces the compressibility of the system compared to thatmore » of the parental empty one. Additionally, the structure of CO₂-loaded silicalite-1 was monitored at high pressures and temperatures, and its thermal expansivity was estimated.« less

The crystal structure of CO₂-filled pure-SiO₂ LTA zeolite has been studied at high pressures and temperatures using synchrotron-based X-ray powder diffraction. Its structure consists of 13 CO₂ guest molecules, 12 of them accommodated in the large α-cages and one in the β-cages, giving a SiO₂/CO₂ stoichiometric ratio smaller than 2. The structure remains stable under pressure up to 20 GPa with a slight pressure-dependent rhombohedral distortion, indicating that pressure-induced amorphization is prevented by the insertion of guest species in this open framework. The ambient-temperature lattice compressibility has been determined. In situ high-pressure resistive-heating experiments up to 750 K allow usmore » to estimate the thermal expansivity at P ≈ 5 GPa. Our data confirm that the insertion of CO₂ reverses the negative thermal expansion of the empty zeolite structure. No evidence of any chemical reaction was observed. Finally, the possibility of synthesizing a silicon carbonate at high temperatures and higher pressures is discussed in terms of the evolution of C–O and Si–O distances between molecular and framework atoms.« less

In this paper, we explore the hardening mechanisms in WB4-based solid solutions upon addition of Ta, Mn, and Cr using in situ radial X-ray diffraction techniques under nonhydrostatic pressure. By examining the lattice-supported differential strain, we provide insights into the mechanism for hardness increase in binary solid solutions at low dopant concentrations. Speculations on the combined effects of electronic structure and atomic size in ternary WB₄ solid solutions containing Ta with Mn or Cr are also included to understand the extremely high hardness of these materials.