Defect
Chemistry of the Metal Cation Defects in the p- and n‑Doped SnO<sub>2</sub> Nanocrystalline Films
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Abstract
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 SnO<sub>2</sub>. 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<sup>+</sup>, Cd<sup>2+</sup>, Al<sup>3+</sup>), isovalent
(Ti<sup>4+</sup>), and n-type (Nb<sup>5+</sup>, W<sup>6+</sup>) doped
SnO<sub>2</sub> 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 SnO<sub>2</sub>. 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 (Δ<i>E<sub>D</sub></i>) of the metal cation defects and electron hopping energy (<i>E<sub>H</sub></i>) in the doped SnO<sub>2</sub> 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 SnO<sub>2</sub> are first introduced
here, and the validity of these data are confirmed. What’s
more, the Δ<i>E<sub>D</sub></i> calculated here is
of critical importance for understanding the defect structure of the
metal dopants in the SnO<sub>2</sub>