Probing the correlation between phase evolution and growth kinetics in the oxide layers of tungsten using Raman spectroscopy and EBSD

Abstract

Tungsten, a plasma-facing material for future fusion reactors, may be exposed to air during abnormal operation or accidents. Only limited information is available on the evolution of related oxide phases. This work addresses the effect of substrate orientation on structural variations of tungsten oxides. Annealing experiments in an argon-oxygen atmosphere have been conducted at T = 400°C under varying oxygen partial pressure and oxidation time. A combination of EBSD, Raman spectroscopy and confocal microscopy shows preferential oxidation initially on {1 1 1} base material planes. The oxide scale changes its phase composition dynamically, influencing the kinetics of its growth.

Phase Variation of Ultrathin WO3 Electron‐Transport Layer Prepared by Scalable Langmuir–Blodgett Technique to Boost Efficiency of Dye Sensitized Solar Cells

“…It is to be noted here that the band at lower wavenumber 640–700 cm −1 has been found to be sensitive to the crystal structure, though many WO 3 polymorphs exhibit a dominant band at 805–820 cm −1 . [ 34 ] In addition, bands at 140, 270, and 301 cm −1 appeared, which were assigned to the monoclinic phase of the WO 3 and confirm the XRD data for m ‐WO 3 . Therefore, a phase transformation from hexagonal phase to monoclinic phase occurs when thermal decomposition duration of WO 3,TD‐300 films is increased from 2 to 5 h. The phase transition is in line with the estimated value of refractive index, 1.4–1.5, and is in agreement with the reported values for hexagonal and sub‐stoichiometric monoclinic WO 3 films.…”

Hierarchical WO3–x Ultrabroadband Absorbers and Photothermal Converters Grown from Femtosecond Laser-Induced Periodic Surface Structures

“…44 The flattened bands in the range of 703−727 and 794− 827 cm −1 are attributed to the formation of tungsten oxide crystals in multiple polymorphous states such as the γmonoclinic phase of WO 3 , 45 tri-WO 3 , WO 2 , and o-WO 3 . 43 The broadened band at 635 cm −1 is discovered from all samples, indicating the formation of WO 3−x . 46 Oxygen vacancies can render LSPR property to the tungsten oxide structures, which, in turn, enhance the Raman signals.…”

“…Upon annealing, the deposited particles can easily transit into thermodynamically stable stoichiometric orthorhombic α-WO 3 crystals, so the Raman peaks mainly come from α-WO 3 rather than its underlying structures. Raman peak intensities of 800/1000 °C-annealed W and fs-5W-W samples are significantly enlarged than those of the 600 °C-annealed sample, which allow us to identify more tungsten oxide phases besides α-WO 3 Raman peaks, including 243, 612, and 185/219/377/640 cm –1 originating from tri-WO 3 , WO 2 , and o-WO 3 , respectively . The peaks at 400, 418, and 446 cm –1 belong to other phases of WO 3 .…”

“…Raman peak intensities of 800/1000 °C-annealed W and fs-5W-W samples are significantly enlarged than those of the 600 °C-annealed sample, which allow us to identify more tungsten oxide phases besides α-WO 3 Raman peaks, including 243, 612, and 185/219/377/640 cm −1 originating from tri-WO 3 , WO 2 , and o-WO 3 , respectively. 43 The peaks at 400, 418, and 446 cm −1 belong to other phases of WO 3 . 44 The flattened bands in the range of 703−727 and 794− 827 cm −1 are attributed to the formation of tungsten oxide crystals in multiple polymorphous states such as the γmonoclinic phase of WO 3 , 45 tri-WO 3 , WO 2 , and o-WO 3 .…”

Laser Powder Bed Fusion of Pure Tungsten: Effects of Process Parameters on Morphology, Densification, Microstructure

“…Tungsten (W), the metal with the highest melting point (3695 K), has been widely used in many fields including aerospace, electronics, and medical devices due to its excellent properties such as high melting point, high density, good thermal conductivity, and low thermal expansion coefficient [ 1 , 2 , 3 ]. W is also considered to be a promising candidate plasma-facing material for the divertor devices in the nuclear industry because of its characteristics of sputtering resistance and low tritium retention [ 4 , 5 ].…”