Cation-driven electrical conductivity in Ta-doped orthorhombic zirconia ceramics

This paper is devoted to the study of the electrical conductivity of tantalum-doped zirconia ceramics prepared by spark plasma sintering. In this study, the temperature dependence of conductivity in as-prepared specimens and in those previously annealed in air is determined and compared. A semi-empirical model, which is based on the oxidation states of the cations, has been developed and successfully assessed. According to this, the conductivity is basically controlled by the diffusion of tetravalent zirconium cations in both cases, although the concentration of these species varies drastically with the amount of induced oxygen vacancies. This is a quite unexpected fact, since conductivity is normally controlled by anionic diffusion in zirconia ceramics. This option is forbidden here due to the presence of substitutional pentavalent cations. Therefore, conductivity values are much lower than those reported in trivalent or divalent substitutional cation doped zirconia ceramics.The authors would like to acknowledge provided by several institutions: BMM wants to acknowledge the Spanish Ministry of Science and Innovation through the grant PID2019-103847RJ-I00, as well as the financial support awarded by the Regional government of the ‘Junta de Andalucía’ through the project P18-RTJ-1972. BMM and JIP gratefully acknowledge the financial support provided the Ministry of Science in Spain through the projects MAT2016-77769-R and Gobierno de Aragón, Spain (Grupo Reconocido DGA T02_17R) and the associated EU Regional Development Funds. MLB acknowledges the funding support provided by the projects MAT2015-68078-R and PID2019-107106RB-C32 funded by the Spanish Ministry of Science and Innovation. Finally, DGG and ADR are grateful to the Spanish Ministry of Science for the research funding through the project MAT2015-71411-R.Peer reviewe