Raman and photoelectron spectroscopic investigation of high-purity niobium materials: Oxides, hydrides, and hydrocarbons

Abstract

We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (residual resistivity ratio, ∼300) niobium (Nb) materials used in fabrication of superconducting radio frequency (SRF) cavities for particle accelerators. Raman spectroscopy of Nb materials (as-received from the vendor as well as after surface chemical- and thermal processing) revealed numerous peaks, which evidently show the presence of oxides (550 cm−1), hydrides (1277 and 1385 cm−1: ∼80 K temperature), and groups of hydrocarbons (1096, 2330, 2710, 2830, 2868, and 3080 cm−1). The present work provides direct spectroscopic evidence of hydrides in the electropolished Nb materials typically used in SRF cavities. Raman spectroscopy thus can provide vital information about the near-surface chemical species in niobium materials and will help in identifying the cause for the performance degradation of SRF cavities. Furthermore, photoelectron spectroscopy was performed on the Nb samples to complement the Raman spectroscopy study. This study reveals the presence of C and O in the Nb samples. Core level spectra of Nb (doublet 3d5/2 and 3d3/2) show peaks near 206.6 and 209.4 eV, which can be attributed to the Nb5+ oxidation state. The core level spectra of C 1 s of the samples are dominated by graphitic carbon (binding energy, 284.6 eV), while the spectra of O 1 s are asymmetrically peaked near binding energy of ∼529 eV, and that indicates the presence of metal-oxide Nb2O5. The valence-band spectra of the Nb samples are dominated by a broad peak similar to O 2p states, but after sputtering (for 10 min) a peak appears at ∼1 eV, which is a feature of the elemental Nb atom.

NbOx overlayers protecting a NiMo alloy electrode realizing high-efficiency and durable intermittent water electrolysis

“…2e indicated that no MO stretching vibration signal at 900 cm −1 was detected on the NiMo/Nb surface before the reaction, indicating that the NbO x coating can effectively inhibit the transition process from Mo to MoO 4 2− . In addition, Nb–O–Nb vibration signals belonging to Nb 2 O 5 were detected at 285 cm −1 , 25,26 and vibration signals attributed to Ni–O(H) in the range of 400–500 cm −1 were also observed. Despite some fluctuations in signal strength, likely due to the bubbles generated during the test, no changes in the position of these signals were detected, suggesting that there had been no significant changes in the surface structure.…”

Carbon Formation during Methane Dry Reforming over Ni-Containing Ceria-Zirconia Catalysts

“…The binding energy of Nb 3d 5/2 varies in the range of 206.8–206.9 eV, which corresponds to niobium in the Nb 5+ state. For stoichiometric oxide Nb 2 O 5 , the binding energy of Nb 3d 5/2 lies in the range of 206.2–207.9 eV [ 47 , 48 ].…”

Properties of Nb3Sn films fabricated by magnetron sputtering from a single target

“…2. The peaks were compared to previously reported Raman spectra of Nb 3 Sn, Nb, Nb 2 O 5 , and NbO 2 [29][30][31][32][33][34][35]. The asdeposited film shows a wide Raman peak with its maximum at 189 cm − 1 .…”

“…2(d) becomes hardly visible from the background, due to the decomposition of the Nb 3 Sn and the peak of NbO 2 at 215 cm − 1 becomes the strongest peak. Two more peaks at 160 and 268 cm − 1 appeared as the film is annealed at 1000 • C for 24 h. These two peaks correspond to Nb 3 Sn [30] and Nb [32] respectively. This result of the presence of Nb 3 Sn and Nb after annealing at 1000 • C for 24 h agrees with the XRD data as both Nb and Nb 3 Sn diffraction peaks are seen.…”