Preparing method for lead-free positive temperature coefficient thermistor ceramic

The invention relates to a preparing method for lead-free positive temperature coefficient thermistor ceramic which is sintered under the air atmosphere and has a high Curie temperature, a high liftdrag ratio and low room-temperature resistivity. The formula x(Bi1/2Na1/2)TiO3-yCaTiO3-(1-x-y) BaTiO3+a Li2CO3+bSb2O3 powder is adopted in the method, wherein x=0.01-0.12, y=0-0.20, a=0-0.5 mol%, b=0-0.20 mol%, one or more of Nb2O5, La2O3, Sm2O3 and Nd2O3 compounds serve as a semi-conductive agent, and Al2O3 and TiO2 serve as a sintering aid. An adopted technology comprises the steps that round sheets pressed with the materials are sintered after heat preservation is carried out for 10-30 min at 1250-1380 DEG C in the air atmosphere, are fully sintered and achieve a solid-phase reaction; the surfaces of the sintered round sheets are polished, electrodes are applied, and the PTCR ceramic material is obtained. According to the ceramic material, the room-temperature resistivity is as low as 30 ohm.cm, the Curie temper