Energy-dispersive measurements of diffracted synchrotron radiation as a function of pressure: applications to phase transitions in KCl and KI

Extensive details are presented of an experimental system consisting of a diamond-anvil pressure cell, a Si(Li) detector, a four-axis micropositioning system, and detection electronics assembled for performing energy-dispersive X-ray diffraction measurements with a synchrotron radiation source. Procedures for aligning and calibrating the system at the synchrotron facility are presented and the system is used to examine the first-order structural phase transitions in both KCl and KI. Structural information has been obtained with this system from the high-pressure environment in a fraction of the time normally required. Diffraction peaks could be identified and measured to an accuracy of ±0.1% within 200 s and to an accuracy of ±0.4% within 0.5 s. Optimum ranges for diffraction angles and X-ray photon energies are reported. Volume compressibilities of KCl and KI in the low-pressure (B1 structure) and the high-pressure (B2 structure) phases are given along with information about the hysteresis loop associated with this transition.