GROWTH AND CHARACTERIZATION OF GEL-GROWN LEAD(II)CHLORIDE AND LEAD(II)BROMIDE SINGLE-CRYSTALS

Single crystals of pure and doped lead(II)chloride and lead(II)bromide were grown by gel technique employing a modified two-stage chemical r eaction. Methods to minimise the predomination of needle morphology du ring the growth of these crystals have been investigated and the resul ts are discussed. The grown crystals were characterised by optical tra nsmission spectrum. Undoped and monovalent cation (K+, Na+, Cu+, Ag+ a nd Hg+) doped crystals of PbCl2 and PbBr2 were subjected to d.c. elect rical conductivity studies. Using the log sigma T versus T-1 plot, the activation energies for the migration of anion vacancies in lead(II)h alides are calculated. They are found to be less for the doped crystal s than those of undoped ones.