Hydrothermally Synthesized h-MoO3 and α-MoO3 Nanocrystals: New Findings on Crystal-Structure-Dependent Charge Transport

Abstract

The charge transfer characteristics of metastable-phase hexagonal molybdenum oxide (h-MoO3) and stable-phase orthorhombic MoO3 (α-MoO3) nanocrystals have been investigated for the first time using impedance spectroscopy. The results imply that the metastable phase h-MoO3 displays a 550-fold increase (at 150 °C) in the electrical conductivity relative to the stable phase α-MoO3. The conductivity also increases as the temperature increases from 130 to 170 °C, whereby analysis shows a thermal activation energy (Ea) of ∼0.42 eV. The investigation clearly identifies that the presence of intercalated ammonium ions (NH4+) and crystal water molecules (H2O) in the internal structure of h-MoO3 plays a vital role in enhancing the charge transfer characteristics and showing an ionic conductive nature. Before the impedance investigations, the h-MoO3 and α-MoO3 nanocrystals were successfully synthesized through a wet-chemical process. Here, a controlled one-step hydrothermal route was adopted to synthesize stable-phase...