Dramatic impact of the TiO 2 polymorph on the electrical properties of ‘stoichiometric’ Na 0.5 Bi 0.5 TiO 3 ceramics prepared by solid-state reaction

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2022-01, Vol.10 (2), p.891-901
• Main Authors: Yang, Fan, Hu, Yidong, Hu, Qiaodan, Steiner, Sebastian, Frömling, Till, Li, Linhao, Wu, Patrick, Pradal-Velázquez, Emilio, Sinclair, Derek C.
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/D1TA09668K

Bulk conductivity ( σ b ) values of nominally stoichiometric Na 0.5 Bi 0.5 TiO 3 (NBT) prepared by solid-state reaction collated from literature show random variation between 10 −6 to 10 −3 S cm −1 (at 600 °C). This makes it challenging to obtain reliable and reproducible performances of NBT-based devices, especially as the underlying reason(s) for this variance are not fully understood. Here we report the dramatic impact of the TiO 2 reagent, in particular, the polymorphic form of TiO 2 on the electrical conductivity and conduction mechanism of NBT. Based on our solid-state processing route, NBT ceramics prepared by rutile TiO 2 are ionically conductive, and those prepared by anatase TiO 2 are insulating. The dramatic difference in electrical properties of NBT prepared using rutile and anatase TiO 2 is related to the NBT formation process: the intermediate phase Bi 12 TiO 20 is more stable during formation of NBT in the case of anatase TiO 2 , which reduces the volatility of Bi 2 O 3 during solid-state reaction. These results give plausible explanations for the large variation of σ b reported in the literature and highlight the importance of selecting an appropriate TiO 2 reagent when targeting controllable σ b in NBT-based ceramics. For ion-conducting applications (such as in intermediate-temperature solid oxide fuel cells, IT-SOFCs), rutile TiO 2 should be used, and for dielectric applications (such as in multilayer ceramic capacitors, MLCC) anatase TiO 2 should be used.