PARAMAGNETIC POINT-DEFECTS IN SNO2 AND THEIR REACTIVITY WITH THE SURROUNDING GASES .1. INTERACTION OF OXYGEN LATTICE CENTERS WITH VAPOR-PHASE H2O, AIR, INERT AND COMBUSTIBLE GASES, AS REVEALED BY ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY

The formation of oxygen vacancies in powdered SnO2 has been investigated by electron paramagnetic resonance (EPR) spectroscopy. It is suggested that strong resonances at g = 1.89 are responsible for the paramagnetic singly ionized form of the V(O) neutral vacancies. These defects were formed under dry inert atmosphere at temperatures above 673 K, while both under inert wet gas or wet air they become stable at lower temperature (473 K). The maximum amounts of V(O) were observed under dry H-2 (0.5%)-air and moist CO (0.5%)-air mixed gases, again at 473 K. A rationale is given for the role of the vapour-phase H2O in promoting the formation of donor centres and in improving the conductance of SnO2 at relatively low temperatures.