Diamond Anvil cell

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 K 0 and its pressure derivative, , have been determined from the present compression by fitting the third-order Birch–Murnaghan equation of state: K 0=325±9 GPa and . 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.

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes

The reactivity induced in acetylene, benzene and phenylacetylene crystals by the application of high external pressure is discussed. Acetylene, the simplest model system involving the CC triple bond, reacts above 3.0 GPa in the orthorhombic crystal phase. The molecular arrangement in this phase determines the final conformation of the recovered polymer. The role of laser irradiation in branching the polyenic chains, through the dissociation of the double bonds, is revealed. Benzene, the model aromatic molecule, starts to react in the solid state above 23 GPa. A progressive distortion of the rings is observed on increasing pressure up to 50 GPa but the transformation becomes complete, close to ambient pressure, only during the decompression run. An amorphous hydrogenated carbon compound (a-C:H) is formed in this reaction. Laser irradiation with suitable wavelengths reduces the reaction pressure threshold revealing the role of the S1 excited state in driving the high-pressure reaction. Finally, phenylacetylene was taken into account since it is the simplest molecule involving both the triple bond and the aromatic ring and its reactivity could be possibly interpreted according to the previous model systems. Phenylacetylene starts to react in the solid state above 8 GPa. The reaction mainly involves the triple bond of the ethynyl fragment forming polyphenylacetylenic chains. On the basis of the infrared spectra a possible polymer structure is proposed. Copyright © 2003 John Wiley & Sons, Ltd.

The pressure- and anion-dependent electronic structure of EuX (X=Te, Se, S, O) monochalcogenides is probed with element- and orbital-specific X-ray absorption spectroscopy in a diamond anvil cell. An isotropic lattice contraction enhances the ferromagnetic ordering temperature by inducing mixing of Eu 4{\it f} and 5{\it d} electronic orbitals. Anion substitution (Te $\to$ O) enhances competing exchange pathways through spin-polarized anion {\it p} states, counteracting the effect of the concomitant lattice contraction. The results have strong implications for efforts aimed at enhancing FM exchange interactions in thin films through interfacial strain or chemical substitutions.

An easily assembled setup employing diamond anvil cell, stainless steel gasket and leads, and mylar embedded Al2O3 (alumina) pressure medium for the measurement of electrical resistance of materials under pressure is described. The use of a mylar sheet prevents the alumina layer from sticking to the anvil in the precompacting stage of Al2O3 and also reduces the pressure gradients in the final assembly. The technique is used to reproduce the known transition in Si, Ge, and Fe. The results of measurements of electrical resistance of ytterbium up to 40 GPa are reported. In the hcp phase of ytterbium the electrical resistance increases with pressure. Efforts are made to explain the variation of resistance with pressure from known band structure calculations.