Effect of calcination temperature on the structural, microstructure, and electrical properties of CeO2 nanoparticles as a solid electrolyte for IT-SOFC application

Abstract

This article comprehensively discusses the effect of calcination temperatures such as 400 °C, 600 °C, and 700 °C of the single-phase ceria oxide (CeO2) nanoparticles synthesized via sol–gel chemical root. The first principle calculation performed on the cubic fluorite structure of ceria oxide shows Ce(5d) and O(2p) contributed to the indirect band gap n-type semiconducting response. The structural studies also show the crystallization of CeO2 in the cubic structure with a gradual change in crystallite size, dislocation density, and micro-strain with temperature. The stretching vibration of Ce–O at 437 and 541 cm−1 in the Fourier-transform infrared (FTIR) spectrum reconfirms the monophasic nature of the obtained samples. The morphology of the sintered pellets is strongly affected by varying calcination temperatures, such as lower-temperature calcined materials containing larger grains and vice versa. The X-ray photoelectron spectroscopy (XPS) studies show oxygen vacancies and Ce's mixed states in Ce3+/Ce4+. Arrhenius-type transport behavior was reflected through DC conductivity analysis that reveals the two conduction regions: electrons through Ce's degenerate sites in the region-1 (90–280°C) and oxygen ions in the region-2 (280–410°C). The spectroscopic plots extracted the grain and grain boundary contribution, affecting the electrical properties. The grain boundary has a higher activation energy than the grains due to voids and disordered structures at the interface, similar to DC conduction studies. The sample Ce-4′s blocking factor supports the highest DC conductivity of almost 10−2 S/cm, close to IT-SOFC solid electrolyte conductivity. Therefore, the present study may open the window to commercialize ceria oxide-based solid electrolytes through grain/grain-boundary engineering in IT-SOFCs. © 2024 The Society of Powder Technology Japan