Charge compensation and electrical characteristics of Ta2O5-doped SnO2-CoO ceramics

摘要

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 spinet 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 Ta(2)O(5 )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 Ta2O5-doped SnO2-CoO system. Accordingly, the following charge compensation mechanism is proposed: 3 Sn(IV)(Sn)(center dot)((IV)) reversible arrow Co(II)(sn)('')( (IV)) + 2 Ta(V)(sn)(center dot)((IV)).