Research on the phase transition of (Ba_(0.07)K_(0.93))NbO_3-based PTCR ceramic material

摘要

The phase transition performance and positive temperature coefficient of resistivity (PTCR) effect in Mn-doped (Ba_(0.07)K_(0.93))NbO_3-based ceramic material were investigated. The results showed that an excellent PTCR effect with a resistance anomaly (Rmax/Rmin) up to 5 × 10~3 and a switch temperature (Ts) of approximately 60 ℃ was obtained in the ceramic sample. In contrast to the phase transition of orthorhombic-to-tetrahedral and tetrahedral-to-cubic with an exothermic effect, endother-mic effects were observed near the temperature of the rhombohedral-to-orthorhombic (R-O) phase transition. The XRD results at elevated temperature showed significant cell shrinkage when the lattice structure transferred from the rhombohedral state to an orthorhombic state, accompanied by remarkable internal stress inside the ceramic sample. The XRD results also showed that both the rhombohedral and orthorhombic phase co-existed near the temperature of the R-O phase transition. At this temperature, we observed a considerable dielectric anomaly from the measurement of the temperature dependency of the dielectric constant, which was believed to be from the unique R-O phase transition. The PTCR effect observed in this material was mainly contributed by the anomalous dielectric constant.