LAUSR

Abstract We investigated the effect of pentavalent donor dopant Ta2O5 on microstructure development, electric and dielectric characteristics of SnO2–CoO based ceramics. Already low additions of Ta2O5 (0.05 mol%) effectively reduce the porosity, improve densification and dielectric permittivity and trigger a 3–fold increase in SnO2 growth rate. Rietveld analysis shows that the amount of Co2SnO4 spinel phase drops with the addition of Ta2O5 due to incorporation of Co2+ and Ta5+ into SnO2 structure. With higher additions, however, Ta2O5 segregates to the grain boundaries and hinders SnO2 grain growth, which in turn improves electrical properties. TEM/EDS analysis shows that above 0.5 mol% of Ta2O5 the Co:Ta ratio in SnO2 grains is constant 1:2, which means that a twice lower amount of Ta5+ is incorporated in the SnO2 structure compared to the Nb2O5-doped SnO2–CoO system. Accordingly, the following charge compensation mechanism is proposed: 3 Sn(IV)S˟n (IV) ⇋ Co(II)Sn (IV) + 2 Ta(V)˙Sn (IV).