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We report the crystallite-size-dependency of the compressibility of nanoceria under hydrostatic pressure for a wide variety of crystallite diameters and comment on the size-based trends indicating an extremum near 33 nm. Uniform nano-crystals of ceria were synthesized by basic precipitation from cerium (III) nitrate. Size-control was achieved by adjusting mixing time and, for larger particles, a subsequent annealing temperature. The nano-crystals were characterized by transmission electron microscopy and standard ambient x-ray diffraction (XRD). Compressibility, or its reciprocal, bulk modulus, was measured with high-pressure XRD at LBL-ALS, using helium, neon, or argon as the pressure-transmitting medium for all samples. As crystallite size decreased below 100 nm, the bulk modulus first increased, and then decreased, achieving a maximum near a crystallite diameter of 33 nm. We review earlier work and examine several possible explanations for the peaking of bulk modulus at an intermediate crystallite size. [ABSTRACT FROM AUTHOR]

Abstract: A high pressure diffraction study, from ambient to 50GPa, has been carried out on nanocrystalline TiN/amorphous BN nanocomposite materials prepared by plasma chemical vapor deposition. The compressibilities of these materials were found not to be significantly different from TiN. A large amount of biaxial and isotropic strain was found to build up on pressurization which continued to exist after depressurization and annealing indicating a permanent deformation under high pressure. This permanent deformation is located in the grain boundaries and is reduced by the presence of amorphous BN. [Copyright &y& Elsevier]

Abstract: Earlier measurements of elastic moduli of nc-TiN/a-Si3N4 nanocomposites of different composition and hardness by means of vibrating reed and surface Brillouing scattering, that yield Young’s and shear modulus, as well as the Poisson’s ratio, have been confirmed by high-pressure X-ray diffraction measurements, that yield bulk modulus. It is found that elastic moduli of all measured samples are essentially the same within relatively small error of measurements, and only slightly lower than that of pure TiN. The nanocomposites are superhard thanks to their unique nanostructure with strengthened SiN x interface. [Copyright &y& Elsevier]

Abstract: Synchrotron X-ray diffraction data was collected from a sample of monocarboaluminate 3CaO·Al2O3·CaCO3·11H2O from ambient pressure to 4.3GPa. The refined crystal structure at ambient pressure is triclinic with parameters a=5.77(2) Å, b=8.47(5) Å, c=9.93(4) Å, α=64.6(2)°, β=82.8(3)°, γ=81.4(4)°, and space group of P1 or P . It showed some degree of perfectly reversible pressure-induced dehydration with a non-hygroscopic pressure-transmitting medium. However the dehydration effect does not critically affect a bulk modulus due to its strong framework. The isothermal bulk modulus of monocarboaluminate was found to be 53(5)GPa and 54(4)GPa with 3rd order and 2nd order Birch-Murnaghan Equation of state, respectively. That value is higher than for any other reported AFm or AFt phase. The pressure–volume behavior of the monocarboaluminate was compared with that of previous studied hemicarboaluminate. [Copyright &y& Elsevier]

Abstract: The compressibilities of two AFm phases (strätlingite and calcium hemicarboaluminate hydrate) and hydrogarnet were obtained up to 5GPa by using synchrotron high-pressure X-ray powder diffraction with a diamond anvil cell. The AFm phases show abrupt volume contraction regardless of the molecular size of the pressure-transmitting media. This volume discontinuity could be associated to a structural transition or to the movement of the weakly bound interlayer water molecules in the AFm structure. The experimental results seem to indicate that the pressure-induced dehydration is the dominant mechanism especially with hygroscopic pressure medium. The Birch–Murnaghan equation of state was used to compute the bulk modulus of the minerals. Due to the discontinuity in the pressure–volume diagram, a two stage bulk modulus of each AFm phase was calculated. The abnormal volume compressibility for the AFm phases caused a significant change to their bulk modulus. The reliability of this experiment is verified by comparing the bulk modulus of hydrogarnet with previous studies. [Copyright &y& Elsevier]

Abstract: Tantalum nitrides were formed by reaction of the elements at pressures between 9(1) and 12.7(5)GPa and temperatures >1600–2000K in the laser-heated diamond anvil cell. The incorporation of small amount of nitrogen in the tantalum structure was identified as the first reaction product on weak laser irradiation. Subsequent laser heating led to the formation of hexagonal -Ta2N and orthorhombic -Ta2N3, which was the stable phase at pressures up to 27GPa and high temperatures. No evidence was found for the presence of -TaN, -TaN, -TaN, Ta3N5-I or Ta3N5-II, which was predicted to be the stable phase at GPa and K, at the -conditions of this experiment. The bulk modulus of -Ta2N3 was determined to be GPa from a 2nd order Birch–Murnaghan equation of state fit to the experimental data, while quantum mechanical calculations using the density functional theory gave a bulk modulus of GPa for a 2nd-order fit or GPa and for a 3rd-order fit. The values show the large incompressibility of this high-pressure phase. From the DFT data the structural compression mechanism could be determined. [Copyright &y& Elsevier]

Abstract: The formation of a hexagonal rhenium carbide phase, Re2C, from the elements has been studied in a laser heated diamond anvil cell in a P, V range of 20–40GPa and 1000–2000K. No indication for the existence of cubic rhenium carbide, as suggested in the literature, or any other phase was found and Re2C is the only phase formed in the Re–C system up to around 70GPa and 4000K. A fit of a 3rd-order Birch–Murnaghan equation of state to the Re2C P, V-data results in a bulk modulus of GPa (). The linear compressibility of Re2C along [001] ( GPa) is significantly larger than the compressibility in the (001) plane ( GPa ). Based on the observations for Re2C, we predict the structure and elastic properties of an analogous Os2C phase, which is, at least in the athermal limit, more stable than any other osmium carbide studied previously by density functional theory based calculations. [Copyright &y& Elsevier]