Investigation of Annealing Process Effects on the Response and Stability of Sprayed Co2SnO4 Film under Ethanol Vapor

Abstract

The ethanol (C2H5OH) vapor detection properties of a layer of cubic spinel cobalt stannate as-prepared Co2SnO4 (denoted as CTOas), elaborated by a low-cost spray pyrolysis method, were investigated before and after an annealing process. The response of layers under ethanol vapors of different concentrations exhibited a stable behavior in a dry atmosphere at the optimum working temperatures. The elaborated nanomaterials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), direct current measurement (DC) and impedance spectroscopy techniques (AC). After the annealing process of pure CTOas, an n-type to p-type conductivity switch was observed and attributed to Co3O4 apparition in the Co2SnO4 structure. The layer’s ethanol response increased and became more stable after annealing. The stability was measured over a period of three months. DC and AC investigations allowed us to propose a detection mechanism involving grain boundary regions in a Co2SnO4/Co3O4 composite obtained after annealing (denoted as CTOann). According to its stable and receivable sensing response, the Co2SnO4/Co3O4 composite could be considered as a promising novel sensitive layer for ethanol gas sensors.