Structural dielectric and electrical conducting properties of KB´B´´O6 (B´=Nb, Ta; B´´=W, Mo) ceramics

Ga2Se3 and Ga2Se3:Co2+ single crystals were produced via the chemical transport reaction method using Ga, Se, and Co as starting materials and (ZnCl2+I2) as a transport agent. The single crystals then crystallized into cubic structures with a lattice constant of a=5.442? for Ga2Se3 and a=5.672? for Ga2Se3:Co2+. The optical energy gap of the single crystals was found to be 2.070eV for Ga2Se3 and 1.931eV for Ga2Se3:Co2+ at 298K. The temperature dependence of the optical energy gap was fit well with the Varshni equation. Impurity optical absorption appeared in Ga2Se3:Co2+. It was described, by the framework of the crystal field theory, as appearing due to electron transition between the energy levels of the Co2+ ion sited in Td symmetry.