Influence of Sb, In and Bi dopants on the response of ZnO thick films to VOCs

Pure ZnO nanoparticle and doped-ZnO nanoparticles with Sb, In, Bi, In–Sb and In–Bi, were prepared by the renovated hybrid induction and laser heating (HILH). The morphological characteristics, phase structure and chemical state of nanoparticles were characterized by TEM, XRD and XPS, respectively. The microstructure, electrical properties and gas-sensing characteristic of the thick film based on nanoparticles were investigated. It was found that the morphology of nanoparticles was influenced by the doping elements Sb, In and Bi. The doping of In, Sb and In–Sb markedly increased the conductivity of ZnO film and its sensitivity to benzene, toluene and xylene. The former was attributed to the substitution of Zn ions by In ions or/and Sb ions, which resulted in generating more free electrons; the latter was closely related to doped samples accommodating a higher density of chemisorbed oxygen. Bi- and In–Bi codoped ZnO films contained Bi2O3 phase, which resulted in their lower conductivities than that of undoped ZnO, but their optimum sensitivity temperature decreased. The response-recovery time of the films to benzene, toluene and xylene was less than 20 s, except the films containing Sb displaying a longer recovery time.