Supercooled plastic crystals as frustrated elastic domains: Phenomenological theory for cyanoadamantane-family crystals

A cubic crystal with orientationally disordered molecules, which mimics a p lastic crystal of the cyanoadamantane family, under conditions of supercool ing has been assumed to evolve into the metastable tetragonal phase as sugg ested by Ostwald's ''law of stages.'' Representing small domains of local t etragonal structures by elastic dipoles, we have analyzed orientational rel axation of the grains embedded in an isotropic elastic medium. The elastic dipole density-density correlation function has been used to discuss a poss ible ordering of the domains. Implications of the model for elastic propert ies, duffuse scattering, and kinetics of the transformation of the supercoo led plastic crystal have been discussed. The paper offers a contribution to the discussion on how glassy are the molecular crystals with orientational disorder.