Microstructure development in (Co,Ta)-doped SnO2-based ceramics with promising varistor and dielectric properties

• Published in: Journal of the European Ceramic Society Vol. 40; no. 15; pp. 5518 - 5522
• Main Authors: Tominc, Sara, Rečnik, Aleksander, Bernik, Slavko, Mazaj, Matjaž, Spreitzer, Matjaž, Daneu, Nina
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2020
• Subjects: Dielectric properties; Dopants; Microstructures; SnO2 ceramic; Varistors; Varistors; Dopants; Microstructures; SnO2 ceramic; Dielectric properties
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2020.03.062

Following the 3 Sn(IV)Sn(IV)×⇋Co(II)Sn(IV)″+2 Ta(V)Sn(IV)⋅ charge compensation mechanism we optimized densification and electrical properties of Ta2O5-doped SnO2–CoO ceramics. We show that incorporation of acceptor dopant Co2+ in SnO2 is promoted after the addition of donor dopant like Ta5+, whereas any surplus of Co would form secondary Co2SnO4 phase. A balanced addition of both dopants is needed to promote densification, and any surplus of donor dopants that remain present at the grain boundaries retard the grain growth and deteriorate electrical properties. Varistor and dielectric properties are then strongly influenced by donor doping. Optimum varistor properties (α = 40, UT = 272 V/mm, IL = 1.2 μA) were measured for the sample with 1 mol% Ta2O5 and the best dielectric properties (ε = 6525; tan(δ) = 0.057@1kHz) were measured for the sample with 0.10 mol% Ta2O5 with the largest SnO2 grain sizes.