Suppressed Polaronic Conductivity induced Sensor Response Enhancement in Mo doped V2O5 Nanowires

Abstract

In this paper, we show the direct correlation between suppression of polaronic oxygen vacancy defect (Vo) density and gas sensor response of 1 at% Mo doped $V_2O_5$ (MVONW) nanowires. Doping 1 at% $Mo^{5+}$ leads to substitution at the $V^{5+}$ site in $V_2O_5$ nanowires (VONW) and thereby reduction in Vo defects. This in turn affects the charge carrier hopping sites and subsequently enhances the sensor response at lower temperatures ($<320^oC$). The $Mo^{5+}$ dopants lead to the lowering of Fermi energy (EF) towards valence band maxima due to reduced $V_o$ donor density. The polaron suppression is confirmed with activation energy of polaron hopping, increasing from 195 meV to 385 meV in VONW and MVONW respectively. As a result, the response to ethanol gas enhanced as the depletion width is widened for the given cross-section of the nanowires. This may lead to large depletion controlled cross-sectional area and thereby better sensitivity. At about $350^oC$ VONW show change in slope of resistance vs temperature (MIT) which is not observed in case of MVONW. This is attributed to presence of enhanced non-stoichiometry of V ion resulting in metallic behaviour and accompanied with sudden rise in sensor response at this temperature. Moreover, the absence of MIT may be attributed to lack of such sudden rise in response in MVONW.