Synthesis of β‐MoO ₃ whiskers by the thermal evaporation method with flowing oxygen gas

Abstract

Abstract β‐MoO 3 is a monoclinic phase of MoO 3 ; it has been shown to be a promising material that can replace α‐MoO 3 in chemical, optical, electronic, and electrochromic applications. However, the difficulty in synthesizing β‐MoO 3 with a one‐dimensional (1D) morphology has limited its use in applications requiring a large specific surface area. In the present work, β‐MoO 3 whiskers were prepared by thermally evaporating α‐MoO 3 powder in a tube furnace at temperatures ( T f ) from 750 to 1000°C and under flowing O 2 gas. The collected samples were identified as mainly β‐MoO 3 by X‐ray diffraction measurements, and the highest purity β‐MoO 3 was obtained at T f = 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‐MoO 3 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‐MoO 3 whiskers were compared with α‐MoO 3 powder via the X‐ray photoelectron spectroscopy characterization method. By elucidating the β‐MoO 3 whisker synthesis mechanism, this research provides guidance for the large‐scale production of β‐MoO 3 whiskers.