Evidence of the (110), (040), and (021) Plane Tuning in the MoO ₃ Crystal Structure via Facile Rapid Vapor Synthesis in Air

High Resolution Image Download MS PowerPoint Slide The (110), (040), and (021) planes of α-MoO 3 are commonly observed in X-ray diffraction (XRD) patterns between 2θ = 20° and 30°, exhibiting varying relative amplitudes under different synthesis techniques. Although prior studies have noted these variations, their specific impact on structural properties remains unexplored. This study investigates how the relative amplitude of the (110), (040), and (021) is modulated via the modified rapid vapor synthesis of α-MoO 3 in air, influencing morphological and structural properties. XRD analysis revealed an 18-fold enhancement in the amplitude of the (040) upon annealing at 750 °C, annihilating the (110) and (021) planes. Therefore, the (110), (040), and (021) amplitude tuning characteristics can be categorized as (i) tensile strain (T ≤ 600 °C) and (ii) compressive strain (T ≥ 650 °C), driven by lattice volume expansion (oxygen loss) and lattice oxygen replenishment, respectively. Overall, elevated temperatures drive systematic exponential decay and growth in the valence band ( E VB = 1.95 to 1.83 eV, 1.82–1.72 eV) and conduction band ( E CB −1.15 to −1.03 eV, −1.02 to −0.92 eV), corroborating the red-shift in both the direct and indirect band gaps. MoO 3 @500 °C exhibited superior optical stability and sensing capability in aqueous acetone and ethanol. Upon exposure to acetone, the optical peak intensity increased and shifted from 295 to 299 nm, while ethanol quenched both absorption peaks. This work provides novel insights into crystallographic control for advanced applications and complements the existing understanding of MoO 3 .