W2O3I4 and WO2I2: metallic phases in the chemical transport reaction of tungsten

摘要

The crystal structures of the hitherto unknown phase W2O3I4 and of WO2I2, a compound that is known to play an important role in the chemical vapor transport of elemental tungsten are reported. We demonstrate that WO2I2 transforms into W2O3I4, and then into WO2 with increasing temperature. Crystals of WO2I2 appear as thin platelets, showing metallic luster; crystals of W2O3I4 appear as black colored needle-shaped platelets. Both compounds adopt layered structures; electronic band structure calculations reveal metallic conductivity for W2O3I4 and surprisingly also for WO2I2.