fig4

Figure 4. (A) Schematic representation of large grain and grain boundary area, along with routes for ionic conduction. Reproduced with permission^[63] Copyright 2007 Elsevier, (B) ionic conductivity comparison of various compositions [Ln₂O₃ (Ln = lanthanide)-doped ZrO₂] at 1,000 °C. Reprinted with permission^[64] Copyright 2000 Elsevier, (C) HAADF image of grain boundary of CeO_2-δ@CeO₂ core-shell, (D) mapping of Ce at the interface (E) ration of Ce⁴⁺/Ce³⁺ at the interface. Reprinted under the terms of the CC BY 4.0 License Copyright 2019, Published by Springer Nature^[67]. (F) Voltage-current density-power density plot SrTiO₃ at different temperatures (450, 500, 550 °C). Reprinted from Ref.^[68] with permission from the Royal Society of Chemistry, 2019.