Defect Chemistry of the Metal Cation Defects in the p- and n-Doped SnO2 Nanocrystalline Films

Cationic interstitial and substitutional defects, which serve as a key role in shaping the material's performance, are considered as two kinds of important defect structures in the doped SnO2. To give a clear characterization of such metal cation defects, temperature-dependent electrical conduction measurement by the high throughput screening platform of gas-sensing materials is carried out, for the first time, to perform the defect structure studies of the p-type (Li+, Cd2+, Al3+), isovalent (Ti4+), and n-type (Nb5+, W6+) doped SnO2 nanocrystalline films in the oxygen-free atmosphere. The temperature-dependent measurements indicate that subtle induced impurities are capable of evidently modifying the electrical conduction mechanism of the SnO2. In terms of the small-polaron hopping mechanism, an improved defect chemical model is proposed in which the properties of the metal cation defects are explicitly depicted. Values for the ionization energy (ΔED) of the metal cation defects and electron hopping energy (EH) in the doped SnO2 are extracted by fitting the experimental data to the defect model. These data that reflect the nature of the metal cation defects and their effects on the electronic structure of the SnO2 are first introduced here, and the validity of these data are confirmed. What's more, the ΔED calculated here is of critical importance for understanding the defect structure of the metal dopants in the SnO2.