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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 KC1 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 ?/0 within 200 s and to an accuracy of +_0"4?/o within 0-5 s. Optimum ranges for diffraction angles and X-ray photon energies are reported. Volume compress/b/l/ties of KCI 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.

A number of improvements in a facility developed over the past three years at the Stanford Synchrotron Radiation Laboratory for the study of pressure and/or temperature effects on materials are described. These include improved beam collimation to both reduce background and eliminate gasket scatter, a remote, pneumatically operated pressurizer, and introduction of a variety of electronics hardware to allow both computer control of experiments and on-line data analyses. Considerations are given to the possible effects of heating of the pressure cavity by the incident beam and to possible fluctuations of the incident beam intensity/energy profile. In both cases, there was no evidence to indicate that these phenomena warranted any further consideration, i.e., they are not considered to be problems in terms of analyzing the data. Extended measurements of a well-defined diffraction peak indicated that a considerable improvement over our earlier work has been realized in terms of the precision in the determination of the energy of the peak, viz., a precision of better than 0.04% for measurement periods as short as 10 s; the estimated precision in the net peak area is less than 3%. The system was used to examine the kinetics of the B1-to-B2 pressure-induced phase transition in KBr. The volume change in the two-phase region is measured to be 10.41%±0.10%, in excellent agreement with most of the previous measurements. A plot of the time dependence of the growth rate of the high-pressure phase indicates that the phase transformation can be described by the Avrami equation. Constants for the phase transition kinetics are given.