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.