PREMELTING IN ORIENTATIONALLY DISORDERED MOLECULAR-CRYSTALS - A REAPPRAISAL

Premelting in polycrystalline samples of some orientationally disordered crystals has been reexamined using the wide-line proton NMR technique and a high resolution-high field Fourier transform spectrometer. It is shown that, as long as the absorption line is not fully dominated by lattice self diffusion, a composite line is observed close to melting. This can be interpreted in terms of an extended defects (such as grain boundaries) premelting model. Direct evidence of internal premelting cannot be provided for three of the most plastic solids, presumably because of the technique used here rather than a fundamentally different behaviour of these particular materials.