Ca12Al14O33 material was prepared by two new methods with optimized microstructures and improved electrical properties compared to the solid-reaction method.

Mayenite Ca12Al14O33, as an oxide-ion conductor, has the potential of being applied in many fields, such as solid-oxide fuel cells. However, its relatively low oxide-ion conductivity hinders its wide practical applications and thus needs to be further optimized. Herein, a new recently developed glass crystallization route was used to prepare a series of Ga-doped Ca12Al14–x Ga x O33 (0 ≤ x ≤ 14) materials, which is not accessible by the traditional solid-state reaction method. Phase evolution with the content of gallium, the corresponding structures, and their electrical properties were studied in detail. The X-ray diffraction data revealed that a pure mayenite phase can be obtained for 0 ≤ x ≤ 7, whereas when x > 7, the samples crystallize into a melilite-like orthorhombic Ca5Ga6O14-based phase. The electrical conduction studies evidence no apparent enhancement in the total conductivity for compositions 0 ≤ x ≤ 7 with the mayenite phase, and therefore, the rigidity of the framework cations and the width of the windows between cages are not key factors for oxide-ion conductivity in mayenite Ca12Al14O33-based materials, and changing the free oxygen content through aliovalent cation substitution may be the right direction. For compositions with a pure melilite-like orthorhombic phase, the conductivities also mirrored each other and are all slightly higher than those of the mayenite phases. These melilite-like Ca5Ga6O14-based materials show mixed Ca-ion, oxide-ion, and electron conduction. Furthermore, the conduction mechanisms of Ca ions and oxide ions in this composition were studied by a bond-valence-based method. The results suggested that Ca-ion conduction is mainly due to the severely underbonded Ca3 ions and that the oxide ions are most likely transported via oxygen vacancies.

Herein, the phases, defect formation energies, and electrical properties of nominal Sn‐doped LaNb1–xSnxO4–0.5x and A‐site deficient La1–xNbO4–1.5x materials are reported. LaNb1–xSnxO4–0.5x shows a solid‐solution limit close to x = 0.03 with the defect formation energy of ≈4.13 eV. Higher conductivities are observed under wet than dry conditions, suggesting a considerable protonic contribution in the Sn‐doped materials. The calculated defect formation energy of ≈9.18 eV for creating La vacancies in La sublattice in LaNbO4 agrees well with the fact that there are mixed dominating parent LaNbO4 and minor orthorhombic La0.33NbO3 phases in nominal La1–xNbO4–1.5x samples. The electrical property studies reveal no proton conduction but strong n‐type electronic conduction in La1–xNbO4–1.5x from the minor La0.33NbO3 phase.

Apatite‐type rare earth silicate with high oxygen ion conductivity are attractive materials for their wide potential applications, such as being used in solid oxide fuel cells as electrolytes. Herein, a series of new apatite‐type oxide ion conductors Ce9.33+xSi6O26+δ (x = 0.43, 0.67, 1.03) have been prepared, with their phases, stabilities, electrical properties, and conducting mechanisms been thoroughly studied. The results reveal that these materials are stable under inert or reducing atmospheres, but decomposed under an oxidizing environment at elevated temperatures. The combined alternative current and directive current techniques reveal dominating oxide ion conductions and minor electronic conductions in them. The bond‐valence‐based method is applied to investigate the possible oxide ion migration pathways and disclose the main contribution from interstitial oxygens, which locate between two neighboring tetrahedral SiO4 units and enable the oxide ion transporting among them along the c‐axis direction, whereas the intrinsic channel oxygens show an inferior responsibility for the oxide ion conductivities.