Synthesis of β‐MoO3 whiskers by the thermal evaporation method with flowing oxygen gas

• Published in: Journal of the American Ceramic Society 2022-03, Vol.105 (3), p.1622-1628
• Main Authors: Ngo, Chu Minh, Nguyen, Hieu Duy, Saito, Nobuo, Do, Thi Mai Dung, Nakayama, Tadachika, Niihara, Koichi, Suematsu, Hisayuki
• Format: Article
• Language: English
• Subjects: chemical vapor deposition; crystal growth; Electrochromism; Image analysis; molybdenum disilicide; Molybdenum trioxide; nanowires; Phase diagrams; Photoelectrons; Temperature distribution; Tube furnaces
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.18192

β‐MoO3 is a monoclinic phase of MoO3; it has been shown to be a promising material that can replace α‐MoO3 in chemical, optical, electronic, and electrochromic applications. However, the difficulty in synthesizing β‐MoO3 with a one‐dimensional (1D) morphology has limited its use in applications requiring a large specific surface area. In the present work, β‐MoO3 whiskers were prepared by thermally evaporating α‐MoO3 powder in a tube furnace at temperatures (Tf) from 750 to 1000°C and under flowing O2 gas. The collected samples were identified as mainly β‐MoO3 by X‐ray diffraction measurements, and the highest purity β‐MoO3 was obtained at Tf = 1000°C. Scanning and transmission electron microscopy observations showed that whiskers with a width of 10 nm were successfully synthesized by this method. The whiskers were confirmed to be β‐MoO3 via lattice image analysis. Measurements of the temperature distribution in the tube furnace and comparisons with the Mo–O phase diagram led to the conclusion that the whiskers formed via a vapor–solid route. Prepared β‐MoO3 whiskers were compared with α‐MoO3 powder via the X‐ray photoelectron spectroscopy characterization method. By elucidating the β‐MoO3 whisker synthesis mechanism, this research provides guidance for the large‐scale production of β‐MoO3 whiskers.