The Study of Batio3 Based Lead-free Piezoelectric Ceramics
|Course||Microelectronics and Solid State Electronics|
|Keywords||barium titanate （BaTiO3） Curie temperature phase transition internal stress|
Temperature stable barium titanate BaTiO3 based dielectric materials have been intensively investigated owing to their high dielectric constant, stable permittivity temperature characteristic. BaTiO3 was also the first developed piezoelectric ceramic and is still widely used now.In the modern industrial system, lead-based piezoelectric ceramics accounted for most of the market, this is because barium titanate has some shortcoming, while lead-based piezoelectric ceramics have higher piezoelectric properties, higher Curie temperature and so on. So the lead-based piezoelectric ceramics are widely used in various types of electronic devices. However, piezoelectric materials containing lead have human health and environmental harm. So the development of lead-free piezoelectric ceramics research is an urgent and significant task, what has attracted wide attention of the scholars. From this point of view, this paper will ascertain the study of the lead-free piezoelectric ceramics. For xBiFeO3–（1-x）BaTiO3 system, X-ray diffraction data showed that 2–8mol%BiFeO3 can dissolve into the lattice of BaTiO3 and form single phase. The crystal structure changes from tetragonal to cubic phase. Scanning electron microscope images indicated that the ceramics have compact and uniform microstructures, and the grain size of the ceramics decreases with the increase of BiFeO3 content. Dielectric constants were measured as functions of temperatures （25 to 200℃）. With rising addition of BiFeO3, the Curie temperature decreases. For the sample with x = 0.08, the phase transition occurred below room temperature. The diffusivity parameterγfor compositions x = 0.02 and x = 0.07 is 1.21 and 1.29, respectively. The relaxor-like behaviour is enhanced by the BiFeO3 addition.This paper use the way of increasing the internal stress to enhance the Curie temperature of BaTiO3. Both of cordierite and glass were added to barium titanate. The cordierite was used for producing the internal stress between barium titanate grains, and glass for reducing the sintering temperature to prevent other materials reaction under high temperature. The cordierite and glass powders were prepared by the sol–gel method. We designed three different formulations. They are 5wt%G-5v%C-95v% BT, 5wt% G-10v% C-90v% BT and 5wt% G-15v% C-85v%BT, respectively. The dielectric constants were measured in a temperature range between 30℃and 200℃. By the results, when 5% glass by weight and 10% cordierite by volume were doped, the highest Curie temperature of barium titanate was obtained, increased 5.2℃than pure BaTiO3.