Metastable Phase Formation of Indium Monochloride from an Amorphous Feedstock

We have studied the structural evolution of crystalline InCl starting from an amorphous deposit, generated by PVD on a sapphire substrate kept at 196 and 228 degrees C. The first crystalline modification occurred at heating up to 100 degrees C and was identified as -InCl, the high temperature modification. Formation of metastable -InCl at the conditions given can only be rationalized by assuming control of phase formation by more efficient nucleation of the metastable, low density polymorph in accordance with the Ostwald-Vollmer rule. At 70 degrees C the system becomes sufficiently activated that the equilibrium polymorph -InCl occurs, which in a reversible process finally transforms to -InCl. During subsequent cooling to room temperature the -InCl is recovered.