Characteristic crystal growth from amorphous WO3 film by vacuum heating

Selective growth of WO₂, W and WO_3?x crystals from amorphous WO₃ film by vacuum heating at 400–900°C was clarified. The grown WO_3?x crystals were incommensurate structure based on crystallographic share structure. The growth process of WO₂ crystal in the amorphous film was directly observed at high temperature in the electron microscope. The growth front of the WO₂ crystal consumes WO₃ microcrystallites with various orientations. The growth speed of the WO₂ depended on WO₃ microcrystallites orientation. The origin of the wavy growth front of WO₂ was due to an orientation dependence of the WO₃ microcrystallites.