Under certain conditions the six-phase tungsten oxide（h-WO₃）can exist in stable form. When annealing temperature exceeds 400℃, it can turns into monoclinic system（γ-WO₃）. 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-WO₃）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, W⁶⁺  exists in the center part of it. O₂ as anion distribute in the other eight edges. Actually, W⁶⁺  often deviates from the center part, the whole structure turns into tetragonal crystal（α-WO₃）, 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 graphs of tungsten oxide, testing equipments are: ICP-AES Spectrograph, X-ray Powder Diffractometer, TSM-6360 LV scanning electron microscope, MICROPLUS laser diffraction particle size analyzer.

In a word, tungsten oxide has various crystalline forms, its transition can affect its property, tungsten oxide crystalline form can largely affects tungsten carbide property. Due to this factor, tungsten oxide can be applied in many fields because of its multi-properties.

With the continuous development and progress of the welding industry, the reliability and stability of the electrode material is proposed more stringent requirements. Rare earth doped tungsten electrode with its high melting point, low electron work function, excellent thermal electron emission property, as the main material in place of thorium tungsten electrode. Besides, it successful replaces thoriated tungsten electrodes used in the small-scale welding. But in AC it has poor arcing property, short service life and other problems. In general, the arcing performance of the tungsten electrode doped with three rare earth oxides is superior to tungsten electrodes doped with single rare earth oxides. In rare earth doped tungsten electrode, ternary complex is better than binary complex.

In the late 1980s, a group of Japanese scholars have made some progress in the development of new tungsten electrode material, particularly in rare earth doped tungsten electrode material. They have operated a lot of work on electrode component design, performance comparison and mechanism study found tungsten electrode doped with two rare earth oxides can improve the performance of the tungsten electrode. For the binary rare earth tungsten electrodes, CeO₂: Y₂O₃ = 1: 3 (CeO₂ 0.5%, Y₂O₃ 1.5%), Ce₂O₃: La₂O₃ = 1: 1, La₂O₃: Y₂O₃ = 1: 3, has better performance and durability property. 1: 3 (La₂O₃ + Y₂O₃) tungsten electrode after 4h (180A) arcing still has good performance and arcing 10h durability remains better condition than single rare earth doped electrode.

For the ternary tungsten electrodes, the best rare earth oxide ratio is CeO₂: La₂O₃: Y₂O₃ = 1: 1: 3. This electrode having good operating performance can sustain 10h (180A) operating. In rare earth doped tungsten electrodes, this electrode having low operating temperature, high electron emissivity, lowest electron work function and other properties, the overall performance is more prominent.

Thoriated tungsten electrodes exists radioactive and long-term using will harm to humans and the environment, therefore developed rare earth doped tungsten electrodes having a similar performance with thorium tungsten electrodes use in welding field. Rare earth doped tungsten electrode having high melting point, low work function and good welding performance and gradually become the new favorite material in welding, cutting, thermal spraying and vacuum electric field.

Tungsten electrode doped with single rare earth oxides
Tungsten electrode doped with single rare earth oxides was first invented in the 1980s. It doped rare earth oxide La2O3, Y2O3, CeO3 into tungsten oxide after reduction, sintering and machining to produce a variety of tungsten electrodes. In practice, we found that this electrode have good arcing and welding property. Tungsten electrode doped with single rare earth oxide is suitable for small current welding. But in high current it service life is not long and the electron emission stability is poor.

Tungsten electrode doped with two rare earth oxides
Tungsten electrodes doped with two rare earth oxides were developed in the 1990s, primarily in order to improve the limitations of the single rare earth doped electrodes. Tungsten electrode doped with two rare earth oxides can carry large current and has large applications range. It has better overall performance than single rare earth doped tungsten electrodes. However, it has poor processing property.

Tungsten electrode doped with three rare earth oxides
Tungsten electrode doped with three rare earth oxides arcing performance, static characteristics and anti-burning property is superior to thoriated tungsten electrode. However, it has poor processing property.