Metastable solid phase at the crystalline-amorphous border: The glacial phase of triphenyl phosphite

The fragile glass-forming liquid triphenyl phosphite (TPP) melts at 298 K, has a glass transition at about 186 K, and can undergo a first order transi tion to a metastable, solid, apparently amorphous phase (denoted the glacia l phase) at about 230 K. Though apparently amorphous (on the basis of preli minary X-ray data), we have shown that the glacial phase is well described as a plastic crystal composed of nanocrystallites; it is thus not a second liquid or glass nor a poor ordinary molecular crystal. This picture of the glacial phase with its close connection to the supercooled liquid from whic h it forms is placed in the context of the frustration-limited-domain theor y of supercooled liquids, and the glacial phase is associated with the defe ct-ordered phase predicted by that theory. In examining the applicability o f this picture, we carried out extensive experimental studies, many of them by means of NMR at both ambient and high pressures, on the glacial phase a nd on the dynamics of the transformations to and from this phase.