Effect of oxygen vacancy engineering on hybrid conduction mechanism in Ce doped La1-xCexBaCo2O5 ceramics

The La 1-x Ce x BaCo 2 O 5 (x = 0.05, 0.1, 0.15, 0.2) thermosensitive ceramics with negative temperature coefficient (NTC) were synthesized using a conventional solid-phase method. X-ray diffraction analysis (XRD) revealed that La 1-x Ce x BaCo 2 O 5 possesses an orthorhombic perovskite structure. Scanning electron microscopy (SEM) showed a uniform and dense ceramic microstructure, with grain size initially increasing and then decreasing as the Ce content rises. X-ray photoelectron spectroscopy (XPS) data reveal the presence of oxygen vacancies and Co 3+ /Co 2+ ion pairs within the material, showing concentrations that increase with Ce content. The resistance temperature profiles indicate the presence of a hybrid conductive mechanism in the material. In the temperature range of 2–20 K, the conductive mechanism of the material conforms to Mott's 3D VRH conduction model. When the temperature is 20–77 K, the conductive mechanism of the material is consistent with the small polariton conduction model. In addition, the mechanism of the mixed effect of oxygen vacancy concentration on the conductivity of the material is explained to elucidate the electron hopping transport conductivity mechanism of NTC thermal ceramics. First-principle calculations demonstrate that oxygen vacancies introduce new impurity energy levels and pathways for electron transport, enhancing the ceramics' electrical conductivity. These findings highlight the ceramic samples' favorable NTC characteristics and electrical conductivity across the temperature range 2–77 K, offering new possibilities for applications in extremely low-temperature NTC thermistors.