Crystal Structures and Phase Transformations of Sodium Pyrophosphate and Sodium Diarsenate

Abstract

<p> An X-ray study of the various phases of anhydrous sodium pyrophosphate has been carried out. The system began with an ordered structure in orthorhombic space group P212121 and ended with a completely disordered structure in hexagonal space group P63/mmc, All the intermediate phases were partially disordered.</p> <p> The crystal structure of the first two phases of the system were determined while the rest were only partially solved due to the complexity of the disorder involved. A discussion on the symmetry aspects of the phase transformations was given and a model for the disorder of the hexagonal phase was proposed.</p> <p> As an integral part of the study the room-temperature phase of sodium diarsenate was also investigated.</p>