Oxygen vacancies in oxidized and reduced vertically aligned α-MoO₃ nanoblades

Abstract

Functionalized materials are highly desired for technological advancements spanning physics, chemistry, materials science, and biology due to their unique electronic properties. One such example is molybdenum trioxide (MoO3), a metal oxide with multiple oxidation states. Manipulating these oxidation states can alter the electronic properties, for instance, defects and electrical conductivity, by several orders of magnitude. In this work, oxygen vacancy-mediated intrinsic defects in vertically aligned a-MoO3 crystals are systematically tuned via thermal treatment under different reducing and oxidizing atmospheres. The positions and the concentration of the oxygen vacancies and restitution of the oxygen ions have been experimentally demonstrated via a range of techniques including electron paramagnetic resonance, X-ray diffraction, and high-resolution electron microscopy. The calculated concentration of the oxygen vacancies in the a-MoO3-x via EPR measurements is in the range of x = 0.004–0.049. The mechanism of the formation of oxygen vacancies in the a-MoO3-x crystal is understood via color center formation and polaron migration models. These oxygen vacancies show no influence on the optical band gap. However, they significantly impact the electrical conductivity on the order of 102 Sm-1 by altering the MoO3 properties from semi-insulating to conducting.