ИСТИНА

The work addresses the problem of the gas sensor response drift and long-term stability of SnO2-based resistive type gas sensors. Combination of n-type donor and acceptor dopants (Nb(V) and Cr(III) cations respectively) in trace amounts is shown to restrain the degradation of gas sensor response towards 5 ppm of methanol during the 30-day continuous sensors operation at 390 oC working temperature and 60% relative humidity (Fig.1). Materials were synthesized by flame spray pyrolysis technique from 0.2M solution of precursors in toluene [1]. Sn (II), Cr (III) and Nb (V) 2-ethylhexanoates were taken as precursors. In total 5 samples were studied – pure SnO2 and SnO2 doped with Cr(III) and Nb(V) 1% mol each, 1% mol Cr(III) with 1, 0.5 and 0.25 % mol Nb(V). The ex-situ characterization of materials aged in the conditions similar to gas sensor experiment by X-ray diffraction (XRD) and BET analysis did not show significant grain growth and effective surface area diminishing. However, the comparison of electron paramagnetic resonance (EPR) spectra of materials revealed important redistribution of defects in the crystal structure of SnO2 grain: Nb (IV) substitutional defects, which were present in the as-prepared materials completely transformed to Nb(V), the concentration of Cr(III) substitutional defects remained almost the same, while the concentration of Cr(VI) surface defects substantially increased. This process of cationic sublattice charge increase appears to be balanced by formation of additional oxygen vacancies, the annealing of which has been reported to contribute significantly to metal oxide gas sensing materials electrical properties drift [2]. [1] V. Krivetskiy et al., Nanomaterials-Basel, 9(5), 728, (2019); doi: 10.3390/nano9050728 [2] Müller, G.; Sberveglieri, G. Chemosensors, 10(5), 171, (2022); doi: 10.3390/chemosensors10050171 The work has been supported by RSCF grant № 22-19-00703.