PERFORMANCE OF DIFFERENT TYPES OF DETECTORS IN A HIGH-PRESSURE X-RAY STUDY OF PHASE-TRANSITION

Phase transitions in praseodymium and lanthanum under pressure have be en studied using a synchrotron powder X-ray diffraction technique. A s tructure refinement of the distorted fee phase of Pr using diffraction data collected with an imaging plate (IP) detector demonstrate that a mong some possible structures the rhombohedral structure with space gr oup R(3) over barm$ best reproduces the observed diffraction pattern. The distorted fcc-fcc phase transition in La was observed as a functio n of the temperature at 23 GPa using a CCD-based detector. A five-minu te exposure sufficiently long to measure the intensities of very weak superlattice reflections from the distorted fee phase, which has been found to transform to the fee phase at 550 K. The performance of the I P and a CCD-based detector are compared and their future developments discussed.