Optimization and coupled absorption effects in diamond anvil energy‐dispersive X‐ray diffraction measurements

Abstract

Optimization of EDXRD measurements using the diamond anvil high-pressure cell vanes with the particular experimental objectives. In the case of P-V-T equation of state studies, the controllable factors are adjusted to optimize the precision and accuracy of the interplanar spacing measurements. The identification of new phases requires the optimization of lattice parameter determinations and the minimization of the effects of thickness on the relative intensities, whereas for reaction rate studies the various factors are adjusted to maximize the absolute intensities of the peaks of interest. I n each of these cases there are trade-offs in the effects of the individual factors that must be made in order to optimize the measurements. Of these factors, the sample absorption is often the most important. For example, profound changes in the relative intensities of diffraction peaks during normal compression studies are caused by the coupled effects of normal sample absorption as the sample thins and the energy dependence of the absorption coefficient. Such changes in relative intensities could be incorrectly attributed to uniaxial stress, residual stress, order-disorder phenomena or element partitioning. Coupled absorption effects in the presence of a powdered, internal standard also have an important bearing on optimizing the relative proportions of admixed standard and sample.