Takayuki Watanabe

Amorphous metal oxide interlayers are widely used to stabilize Li+ transport at battery interfaces, yet the underlying transport mechanisms remain unclear. Here, Li+ transport in amorphous TiOx (a-TiOx) thin films prepared by mist chemical vapor deposition was investigated by comparing electrochemical lithiation with concentration-driven Li+ insertion induced by LiPF6 exposure. Electrochemical lithiation enables redox-assisted, dynamically activated Li+ diffusion accompanied by partial Ti4+ reduction, whereas LiPF6 exposure results in diffusion-limited Li+ transport without significant electronic reduction. Depth-resolved glow discharge optical emission spectroscopy and spectroscopic ellipsometry clearly distinguish these two regimes. In addition, dielectric contrast between the electrolyte, a-TiOx, and graphite is proposed to generate internal electric fields that directionally bias Li+ transport. A Drude-like sub-gap optical response originates from field-induced polarization and localized electronic states rather than metallic conduction. These results highlight the importance of dielectric-field effects in amorphous oxide interlayers for improving interfacial stability and rate performance in lithium-based batteries.

This study presents the successful synthesis of titanium-based transition metal nitride nanoparticles (Ti-Me-N, Me = Ta, Nb, Zr, Cr) using the radio frequency induction thermal plasma method. The mixture of microsized powders of Ti and Ta, Nb, Cr, or ZrN was vaporized in an Ar-NH₃ plasma environment to form Ti-Me-N nanoparticles. The synthesized nanoparticles were crystallized in a cubic rock salt structure, exhibiting a uniform cubic shape and significant agglomeration. Particle sizes were averaged 8-17 nm across the different systems, with Ti and Me elements distributed evenly. The Ti/Me-N bonds in the XPS results also confirmed the successful synthesis of the Ti-Me-N nanoparticles. The formation mechanisms were proposed as a hypothetical model based on thermodynamic analysis and experimental observations. Nanoparticles form rapidly through nucleation, condensation, and coagulation within a high-temperature field characterized by a steep gradient. Nitridation occurs as metal vapors interact with ammonia decomposition products. Model results suggest a possible trend in nucleation behavior, where Ta, Nb, and Zr may supersaturate before Ti, while Ti may nucleate before Cr. This controlled synthesis approach demonstrates the feasibility of the radio frequency induction thermal plasma method for scalable production of high-melting-point Ti-Me-N nanoparticles.

Tantalum nitride nanoparticles were successfully synthesized by induction thermal plasma. The nitrogen sources were controlled to investigate the impacts on nitridation process in thermal plasma. The chemical composition and morphology of the final product were detected by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The formation mechanism was clarified based on the calculation of nucleation temperature and Gibbs free energy change. Tantalum first nucleates at about 3700 K due to the highest nucleation temperature. The nitridation of Ta nuclei is promoted when nitrogen sources change from N₂ molecules to NH radicals. Products transition from oxides and nitrogen-deficient compound Ta₂N mixture to TaN_x with a Ta to N stoichiometric ratio close to 1:1, based on the analysis and calculation result. The amount of nitrogen vacancies in the product can also be effectively controlled by adjusting the injected NH radical concentration. Induction thermal plasma provides a progressive mean to industrial produce nanomaterials applied in the field of advanced coating materials.

This study introduces a method for highly accurate temperature measurement of thermal plasmas with a high-speed camera. Previously reported method enabled precision measurement of temperatures between 17 000 and 30 000 K using only monochromatic intensity at the wavelengths of ionic line spectra. The new approach employs a relative intensity with consideration of line and continuum emissions. This paper achieves two improvements: visualization of a wide temperature range between 10 000 and 30 000 K, and high accuracy of Abel inversion. The wide temperature range can be visualized more accurately by combining wavelengths of atomic and ionic line spectra. Temperature is calculated mainly by the ratio of the line spectra to the continuum emissions. Regularization was applied to Abel inversion to improve the reliability of temperature measurements. Abel inversion with regularization reduces noise by one order of magnitude compared to Abel inversion with smoothing.