Study of electrical conduction mechanisms of CaCu3Ti4O12–MgAl2O4 composite ceramics with NTC effect via in-situ XPS and complex impedance analysis

Abstract

In this study, a series of xMgAl2O4-(1-x) CaCu3Ti4O12 (0.05 ≤ x ≤ 0.20) composite ceramics was fabricated via solid-state method. The X-ray diffraction (XRD) data revealed the coexistence of cubic perovskite and spinel phases, and the scanning electron microscopy (SEM) images highlighted different grain distributions in the produced ceramics. The decrease in resistivity with increasing temperature indicated the NTC (negative temperature coefficient) effect in all samples. As the MgAl2O4 content rose, the values of ρ25, B25/75 and Ea decreased gradually from 3.25 × 108 Ω•cm, 7911 K and 0.6852 eV to 1.46 × 106 Ω•cm, 5669 K and 0.4549 eV, respectively. In situ XPS analysis showed a conduction mechanism based on electron hopping. According to the complex impedance results, both grains and grain boundaries contributed to the NTC effect, and the relaxation behavior of ceramics was mainly due to the oxygen vacancies.