Gas sensor properties of CuGa2O4-based nanocomposites: role of phase composition and microstructure

Practical implementation of machine olfaction and electronic nose systems requires gas-sensing materials with excellent long-term stability for reliable operation in sensor arrays. Promising in this regard nanocrystalline CuGa 2 O 4 -based materials were synthesized by flame spray pyrolysis technique (FSP) and systematically investigated as sensing materials. The effect of post-synthetic annealing temperature on their phase composition, morphology, microstructure and surface chemistry was studied by X-ray diffraction (XRD), total reflection X-ray fluorescence analysis (TXRF), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) with energy dispersive X-ray analysis (EDX). A partially inverted CuGa 2 O 4 spinel structure was identified and confirmed by complementary XPS and Raman analyses, while the formation of an amorphous CuO x phase was revealed depending on the annealing conditions. For the first time, the gas-sensing performance and long-term stability of CuGa 2 O 4 -based materials were evaluated under nearly three months of continuous sensor operation. The sensors were tested against a broad range of inorganic gases (CO, CH 4 and H 2 S) and volatile organic compounds (formaldehyde, methanol, acetaldehyde and acetone) at concentrations relevant to practical gas sensing applications. Gas sensor behavior was found to depend on the phase composition of nanocomposites: the observed inversion from n-type to p-type sensor response with an increase in working temperature is attributed to the presence of an amorphous CuO x phase. Among the investigated materials, the CuGa 2 O 4 -based material annealed at 650 °C exhibited excellent long-term stability, which highlights its potential for reliable electronic nose applications.