ABSTRACT
We have designed a new diamond-anvil cell capable of radial x-ray diffraction to pressures of a few hundred GPa. The diffraction geometry allows access to multiple angles of Ψ, which is the angle between each reciprocal lattice vector g(hkl) and the compression axis of the cell. At the 'magic angle', Ψ≈54.7°, the effects of deviatoric stresses on the interplanar spacings, d(hkl), are significantly reduced. Because the systematic errors, which are different for each d(hkl), are significantly reduced, the crystal structures and the derived equations of state can be determined reliably. At other values of Ψ, the effects of deviatoric stresses on the diffraction pattern could eventually be used to determine elastic constants.
ABSTRACT
A gasketed diamond-anvil high-pressure cell is described which can be used on a four-circle automatic diffractometer to collect x-ray intensity data from single-crystal samples subjected to truly hydrostatic pressures of over 90 kilobars. The force generating system exerts only forces normal to the diamond faces to obtain maximum reliability. A unique design allows exceptionally large open areas for maximum x-ray access and is particularly well suited for highly absorbing materials, as the x rays are not transmitted through the sample. Studies on ruby show that high-pressure crystal structure determinations may be done rapidly, reliably, and routinely with this system.