Tungsten Oxide Crystalline Form Affects Tungsten Carbide Property
Under certain conditions the six-phase tungsten oxide （h-WO 3 ）can exist in stable form. When annealing temperature exceeds 400℃, it can turns into monoclinic system（γ-WO 3 ）. Nano tungsten oxide applied in electric and optical field is different from tungsten oxide bulk. The main differences are phase transition temperature drops evidently, so sometimes orthorhombic tungsten oxide（β-WO 3 ）appears and is stable under room temperature. Chemical stoichiometric number of tungsten oxide seems simple, its phase transition and structure change is complex. The ideal tungsten oxide is octahedron, W 6+ exists in the center part of it. O 2 as anion distribute in the other eight edges. Actually, W 6+ often deviates from the center part, the whole structure turns into tetragonal crystal（α-WO 3 ）, temperature range is T>740℃. For orthorhombic system, 740℃>T>330℃; monoclinic system: 330℃>T>17℃ and triclinic system: 17℃>T>-43℃. Below are SEM gr...