Tin dioxide (SnO₂) is the most-used semiconductor for gas sensing applications. However, lack of selectivity and humidity influence limit its potential usage. Antimony (Sb) doped SnO₂ showed unique electrical and chemical properties, since the introduction of Sb ions leads to the creation of a new shallow band level and of oxygen vacancies acting as donors in SnO₂. Although low-doped SnO₂:Sb demonstrated an improvement of the sensing performance compared to pure SnO₂, there is a lack of investigation on this material. To fill this gap, we focused this work on the study of gas sensing properties of highly doped SnO₂:Sb. Morphology, crystal structure and elemental composition were characterized, highlighting that Sb doping hinders SnO₂ grain growth and decreases crystallinity slightly, while lattice parameters expand after the introduction of Sb ions into the SnO₂ crystal. XRF and EDS confirmed the high purity of the SnO₂:Sb powders, and XPS highlighted a higher Sb concentration compared to XRF and EDS results, due to a partial Sb segregation on superficial layers of Sb/SnO₂. Then, the samples were exposed to different gases, highlighting a high selectivity to NO₂ with a good sensitivity and a limited influence of humidity. Lastly, an interpretation of the sensing mechanism vs. NO₂ was proposed.

Among the various chemoresistive gas sensing properties studied so far, the sensing response reproducibility, i.e., the capability to reproduce a device with the same sensing performance, has been poorly investigated. However, the reproducibility of the gas sensing performance is of fundamental importance for the employment of these devices in on-field applications, and to demonstrate the reliability of the process development. This sensor property became crucial for the preparation of medical diagnostic tools, in which the use of specific chemoresistive gas sensors along with a dedicated algorithm can be used for screening diseases. In this work, the reproducibility of SmFeO₃ perovskite-based gas sensors has been investigated. A set of four SmFeO₃ devices, obtained from the same screen-printing deposition, have been tested in laboratory with both controlled concentrations of CO and biological fecal samples. The fecal samples tested were employed in the clinical validation protocol of a prototype for non-invasive colorectal cancer prescreening. Sensors showed a high reproducibility degree, with an error lower than 2% of the response value for the test with CO and lower than 6% for fecal samples. Finally, the reproducibility of the SmFeO₃ sensor response and recovery times for fecal samples was also evaluated.