Effect of Cr addition on the structure and electrical properties of CaCu3Ti4O12 NTC thermistor.

• Pure and Cr doped CCTO ceramics all have obvious NTC effect. • The addition of Cr 2 O 3 can regulate the resistivity and B values of CCTO ceramic. • The conductive mechanism of CCTO ceramics is the electron hopping. • Both grain and grain boundary contribute to the NTC characteristic of samples. • The relaxation behavior is due to the space charge and dipolar polarization. In the present work, CaCu 3- x Cr x Ti 4 O 12 (CCCTO, 0 ≤ x ≤ 1) ceramics were prepared by a solid-state reaction. The influence of Cr on the structure and electrical properties of the CCCTO ceramics was investigated in detail. X-ray diffractometry (XRD) revealed that all samplesʼ main phases were CaCu 3 Ti 4 O 12 (CCTO), but CuO and CaTiO 3 phases were also found. Cr doping suppressed the abnormal growth of grains, thus the grain size distribution became more uniform with the increase of Cr doping content. The resistance-temperature analysis revealed that all CCCTO ceramics had a noticeable Negative Temperature Coefficient (NTC) effect. The resistivity ρ 30 of the CCCTO ceramics decreased from 1.15 × 106 to 8.73 × 104 Ω cm with an increase in the value of x , along with a decrease in the thermal constant B from 6596 to 3267 K. It was also observed that both the grain and grain-boundary effects contributed to their NTC characteristics. The analysis revealed that the conductivity of the ceramics arose mainly from the electron hopping mechanism. All the samples showed an electrical relaxation behavior. The observations indicated that the structures and electrical properties of CCCTO ceramics could be attuned precisely by adjusting the concentration of the Cr 2 O 3 doping agent. [ABSTRACT FROM AUTHOR]