The wide-bandgap and highly-resistive lead iodide (PbI2) crystalline semiconductor has been considered as a promising room-temperature nuclear radiation detector in environmental applications. The PbI2 single crystals yet grown, however, suffer from problems of phase transformation among its diverse polytypic modifications and formation of polytypes admixture during growth or under post-growth working conditions and from the presence of structural defects and native impurities that normally cause notable deterioration in the performance of devices integrating them. The behaviour of experimental dielectric constant ε1 of undoped melt-grown 2H-polyttype PbI2 single crystals with isothermal annealing temperature Ta (≤94°C) may be taken as a sign for the occurrence of a reversible 2HX12R phase transition in them. However, the effect of reducing the amount of structural native defects and imperfections in such undoped PbI2 crystals by thermal annealing cannot be entirely excluded. The measured room temperature value of ε1 at 1 kHz (~6.5 for Ta = 94°C) of these PbI2 single crystals is compatible with the findings of theoretical dielectric functions model and is consistent with experimental values of ε1 reported by other workers for melt- and gel-grown PbI2 single crystals.
Mahmoud A. Hassan, Mousa M. Jafar, Marie Matuchova and Basim N. Bulos, 2010. An Experimental Evidence of some Lead Iodide Polytypes Compatible with the Dielectric Functions Model. Journal of Applied Sciences, 10: 3367-3373.