ABSTRACT
The NaCl-to-Cmcm phase transition and the Cmcm structure of InAs under high pressure are studied by x-ray diffraction. The lattice parameters and fractional coordinates are given as a function of pressure. We propose a mechanism responsible for this type of symmetry breaking under pressure. We show that the ppσ interactions do not play a major role in the stabilization of the NaCl structure. Consequently the NaCl-to-Cmcm transition occurs only in compounds with a large charge transfer. General conclusions on the behavior of III-V semiconductors under pressure are drawn.
ABSTRACT
Solid bromine has been studied by x-ray absorption spectroscopy experiments up to a maximum pressure of 75 GPa. The data analysis of the extended fine structure reveals that the intramolecular distance first increases, reaching its maximum value at 25+/-5 GPa. From this value the intramolecular distance abruptly begins to decrease evidencing a nonpreviously observed phase transformation taking place at 25+/-5 GPa. A maximum variation of 0.08 A is observed at 65+/-5 GPa where again a phase transition occurs. This last transformation could correspond with the recently observed change to an incommensurate modulated phase. We discuss the possible generalization of the observed new phase transition at 25+/-5 GPa to the case of the other halogens.
ABSTRACT
Americium occupies a pivotal position in the actinide series with regard to the behavior of 5f electrons. High-pressure techniques together with synchrotron radiation have been used to determine the structural behavior up to 100 GPa. We have resolved earlier controversial findings regarding americium and find that our experimental results are in discord with recent theoretical predictions. We have two new findings: (1) that there exists a critical, new structural link between americium under pressure and its near neighbor, plutonium; and (2) that the 5f electron delocalization in americium occurs in two rather than one step.
