Abstract
Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on BaTiO3–(Bi1/2Na1/2)TiO3 (BT–BNT) solid solution were prepared by a conventional solid state reaction method using high purity reagents. BaTiO3 based positive temperature coefficient thermistors doped with BNT showed typical positive temperature coefficient effect. As the elements for achieving semiconducting grains, at a low dopant concentration the grain size is influenced significantly by the donor concentration because of a significant dopant drag on the boundary mobility. Temperature dependence of electrical resistivity was measured and a typical PTCR effect was confirmed in the solid solutions up to 3·0 mol.-% addition of BNT. Especially 1·0 mol.-% BNT added sample indicated superior PTCR properties by optimising the preparation conditions. At high BNT content (≥0·01), the room temperature resistivity increased again with increasing BNT content. A maximum of ρmax/ρmin ratio was obtained at the sintering temperature equal to 1280°C at a given content of BNT. Electrical properties and crystal structure were investigated in order to elucidate the origin of the PTCR effect in this system. The differential scanning calorimetry spectra of this system indicated the transition to cubic from tetragonal crystal structure and the transition temperature increased up to ∼ 170°C with the addition of BNT. Also, the microstructure was observed by SEM technique. In the present study, it was found that the lead free PTCR ceramics in BT–BNT system has extremely similar properties to the conventional lead contained one. Research and development in the field of electroceramics is driven by technology and device applications.
Published Version
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