Dopant-induced cationic bivalency in hierarchical antimony-doped tin oxide nano-particles for room-temperature SO2 sensing

Abstract

The modification of simultaneously existing multiple oxidation states in host lattice cations via the introduction of dopants has been reported for NiO- and Co₃O₄-based gas-sensing materials. However, SnO₂, a widely used material for chemiresistive gas sensing has never been reported with simultaneous presence of Sn²⁺ and Sn⁴⁺ states, in both the absence and presence of dopants. In this work, we demonstrated how antimony doping in a 3+ state triggers the generation of cationic bivalency in tin oxide-based gas sensors, and it is the quantitative presence of unstable Sn²⁺ species that determines the fate of SO₂-sensing responses by antimony-doped tin oxide gas sensors. While the Sn²⁺ content in Sn_0.856Sb_0.144O₂ is 1.2 times less than that of Sn_0.957Sb_0.043O₂, the SO₂ sensing response in the former is 1.2 times more than that in the latter. Greater antimony content in Sn_0.856Sb_0.144O₂ also leads to the generation of additional trap states that result in sequential return of electrons back into the valence band. The reversibility of Sn²⁺ ↔ Sn⁴⁺ during SO₂ adsorption and desorption brings out a new dimension of SnO₂-based chemiresistors besides those already existing.