Table 5.

Influence of additives (in oxide form) in metal oxide matrix on structural and gas sensing characteristics of SnO₂- and In₂O₃-based sensors. Influence on the electrophysical characteristics, i.e., acceptor or donor behavior of the additives, is not considered.

Additive	Effect	Nature
Al2O3; SiO2	Increases sensor response; improves thermal stability	Decrease in crystallite size; decrease in the area of intergrain contacts; increase in porosity
Ag (Ag2O); Cu (Cu2O)	Increases response to H2S, SO2	Two-phase system; phase transformations during gas detection
Fe (Fe2O3)	Increases response to alcohols	Change in oxidation state
Ga(Ga2O3); Zn(ZnO)	Increases sensor response	Decrease in crystallite size; increase in porosity
P, B	Improves selectivity	Creation of new phase
Se	Increases sensor response	Increase in porosity
Ca; K; Rb; Mg	Increases sensor response; improves thermal stability	Decrease in crystallite size
La; Ba; Y; Ce	Improves thermal stability; increases sensor response	Stabilization of crystallite size (creation of new phases); decrease in crystallite size
Transition MOXs: Co; Mn; Sr; Ni	Increases sensor response; improves selectivity	Catalytic effect; change in electron concentration; change in A/D parameters; change in crystallite size

Source: Reprinted with permission from [60]. Copyright 2017 Elsevier.