Critical positive temperature coefficient of resistivity of Li/Y co-doped ZnO ceramics modified by Cr-ions

Abstract

ZnO-based ceramics doped with Li/Y and modified by various contents of Cr-ions, (Zn0.9475Y0.0025Li0.05)1-xCrxO (0 ≤ x ≤ 0.025), were prepared by a wet chemical route followed by a traditional ceramic sintering technology. The effect of Cr-ion content on the electronic conductivity and resistance–temperature characteristics of the prepared ceramics was investigated. All the ceramics have hexagonal wurtzite ZnO structure, and exhibit critical positive temperature coefficient of resistivity (C-PTCR) effect. With various contents of Cr-ions, the maximum temperature coefficient of resistivity (TCR) reaches 61.1%·°C−1 or the resistivity jump log(ρmax/ρmin) is up to 4.74. The critical transition temperature of resistivity can be adjusted in the temperature range of 76–147 °C for different various contents of Cr-ions. The complex impedance analysis shows that the C-PTCR effect of the ZnO ceramics resulted from both grain effect and grain boundary effect. According to the analysis of the dielectric temperature spectra, the ZnO-based ceramics have ferroelectricity at room temperature, and the ferroelectric–paraelectric transition around the critical transition temperature of resistivity during the temperature increases.