Investigations of the bulk defect chemistry of polycrystalline Tin(IV) oxide

Abstract

The bulk defect chemistry of polycrystalline SnO 2 has been investigated systematically by impedance spectroscopy. Nominally pure and In- and Sb-doped materials were shown to be stable in the rutile structure over the entire temperature range (500–900°C). Lattice constants were determined as a function of temperature. Defect chemistry can be described consistently by assuming fully ionized oxygen vacancies and conduction electrons as native defects. In the O 2 partial pressure range between 0.02 and 1 bar, intrinsic behavior was observed with a characteristic exponent of − 1 6 for T > 800°C in nominally pure oxides, whereas at lower temperatures acceptor impurities dominate the conductivity with a characteristic exponent of − 1 4 . In agreement with the defect model proposed, the extrinsic conductivity behavior changes toward intrinsic conductivity behavior with decreasing partial pressure at constant temperature. Heavy In doping (In ′ Sn) increases the acceptor influence, i.e., lowers the (electronic n-) conductivity and extends the extrinsic regime. Weak Sb doping (Sb · Sn) has a donor influence and causes an increase in the conductivity. Since in this case foreign acceptor defects still form the majority of carriers, the transition between extrinsic and intrinsic behavior occurs at lower temperatures but at the same conductivity value. The temperature dependence also reflects this transition and yields enthalpy values for oxygen incorporation of about 1.1 eV per electron.