Development of Lead-Free PTC Thermistor Materials

The electric properties of bismuth- and sodium-modified barium titanate, Ba1-x(Bi1/2Na1/2)x TiO3 (BBNT) were studied as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C. Two semiconductorization processes and their electric properties are described. Lanthanum(La)-doped BBNT ceramics sintered in air still show dielectric behaviors, but Nb-doped ones have a low resistivity ¿RT on the order of 10³Â¿cm at room temperature and show a PTC behaviors. Sintering under low O2 atmosphere produces BBNT ceramics with less than 10² ¿cm compared to those prepared in air. A trial PTC heater constructed using the BBNT semiconducting ceramics demonstrates a comparable performance of those made of the Pb-contained PTC ones. Our current research shows the BBNT ceramics with a switching temperature Ts around 210°C by increasing the (Bi1/2Na1/2) content x of the ceramics.