Phase transition and domain structure in iodoform crystals

Phase transition in an iodoform crystal has been established from the temperature dependence of the Raman spectra of “external” crystal vibrations at 260 K. The transformation mechanism is interpreted under the assumption on the existence in the crystal of domains where dipole moments of the molecules have parallel or antiparallel orientations. Below the phase-transition temperature, the structure is more ordered, and the crystal consists mainly of domains with the parallel orientation of dipole moments of the molecules, whereas above this point, the domains with the antiparallel orientation of dipole moments prevail. The crystal as a whole is not a pyroelectric.