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

Abstract

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.