Search

Pure-phase polycrystalline cadmium tetraphosphide (CdP4) has been successfully synthesized under high pressures in a large volume cubic press, and the pressure-temperature (P-T) formation boundary of CdP4 from the Cd-P binary system has been determined. The equation of state of monoclinic CdP4 has also been evaluated by synchrotron-radiation angle-dispersive X-ray diffraction (ADXRD) under quasihydrostatic compression up to 26.4 GPa in a diamond-anvil cell. The ADXRD data yield a bulk modulus B0 = 94 ± 9 GPa with a pressure derivative B0′ = 8.0. The experimental data are discussed and compared to the results of first-principles calculations. [ABSTRACT FROM AUTHOR]

The compression behavior and stress state of nanocrystalline tungsten boride (WB) were investigated using radial x-ray diffraction (RXRD) in a diamond-anvil cell under non-hydrostatic compression up to 60.4 GPa. The compression properties and stress state are analyzed using lattice strain theory. Experiments were conducted at beamline X17C of the National Synchrotron Light Source. The radial x-ray diffraction data yield a bulk modulus that is qualitatively consistent with density functional theory calculations and demonstrate that WB is a highly incompressible material. A maximum differential stress, t, of about 14 GPa can be supported by nanocrystalline WB at the highest pressure. This corresponds to about 5% of the shear modulus, G, which is smaller than the values of t/G (∼8%-10%) observed for BC2N, B6O, TiB2, and γ-Si3N4 at high pressures. Thus, while WB is highly incompressible, its strength is relatively low at high pressures compared to other hard ceramics. [ABSTRACT FROM AUTHOR]

Diamond and gold powders were compressed nonhydrostatically in a diamond anvil cell and examined by x-ray diffraction using a radial geometry to evaluate the evolution of stresses and strains in these materials to ultrahigh pressure. We found that near isostrain continuity developed across diamond and gold grains under uniaxial compression. The observed mean pressure of diamond powder reached to 360(40) GPa while it was only 31(1) GPa for the polycrystalline gold under the highest load. Polycrystalline diamond can support a microscopic deviatoric stress of 160(18) GPa at about 360 GPa. Due to the deformation of the diamond anvil culet, the macroscopic differential stress of the diamond sample was limited to about 43(8) GPa. There is no evidence that the diamond grains have yielded in our experimental pressure range. [ABSTRACT FROM AUTHOR]

Diamond anvil cell synchrotron X-ray diffraction (XRD) experiments have been carried out on submicron-sized tungsten tetraboride (WB4) at room temperature up to 50.8 GPa with a silicone oil pressure medium. The crystal structure of WB4 remains unchanged up to the highest pressure. The isothermal bulk modulus K0 and its pressure derivative, [image omitted] , have been determined from the present compression by fitting the third-order Birch-Murnaghan equation of state: K0=325±9 GPa and [image omitted] . The high value of the bulk modulus shows that WB4 has high stiffness and/or low-compressibility. Moreover, we also found that the compression behavior of the unit cell axes (a- and c-axes) of WB4 demonstrates an anisotropic nature of compressibility. [ABSTRACT FROM AUTHOR]

The binary tungsten boride, WB, has potential industrial applications as it not only has a high melting point but is generally harder and less compressible than the pure metals. Here, the physical and mechanical properties (phase stability, bulk modulus and compressibility) of WB were investigated by in situ high-pressure x-ray diffraction and theoretical calculations. Its crystal structure still remains stable even at the highest pressure of 63.7 GPa and room temperature for the diamond-anvil cell experiments. The pressure-volume ( P-V ) data were fitted using the Birch-Murnaghan EOS and the Vinet EOS to obtain the isothermal bulk modulus, K 0 = 452 (4) GPa and 451(3) GPa and its pressure derivative, K 0 ′ = 4 (fixed) in the two sets of experiments with two different pressure transmitting mediums (PTMs), respectively. The excellent bulk modulus ( K 0 ) is attributed to the high valence electron density of W atom, the layered and chain-like crystal structure of WB and the strong chemical bonds formed by W and B atoms. Besides, anisotropic compression behavior of the unit-cell axes ( a - and c -axes) of WB is manifested by experimental observations and theoretical calculations. This remarkably elastic property is closely related to the strongly directional bonding between W and B atoms. [ABSTRACT FROM AUTHOR]