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 investigat ed by electron paramagnetic resonance (EPR) spectroscopy. It is sugges ted that strong resonances at g = 1.89 are responsible for the paramag netic singly ionized form of the V(O) neutral vacancies. These defects were formed under dry inert atmosphere at temperatures above 673 K, w hile both under inert wet gas or wet air they become stable at lower t emperature (473 K). The maximum amounts of V(O) were observed under dr y 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 Sn O2 at relatively low temperatures.