Preparation and characterization of textured bismuth ferrite based ceramics

• Main Author: Palizdar, Meghdad
• Published: University of Leeds 2013
• Subjects: 661.0718
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590464

There are many reports in the literature describing the effect of texture on the magnetic and electric properties of materials. Texture is used to provide an enhancement in various properties, compared to random orientation, for example an increase in piezoelectric coefficient, or remnant magnetization. In this work, molten salt and tape casting techniques were employed to synthesis textured bismuth ferrite based ceramics. The fabrication of highly-oriented polycrystalJine ceramics of Bi5Feo.SCOo.5 Ti JOl5 (BFCT), prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets is reported. Electron backscatter images show a secondary phase within the ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from scanning electron microscopy was estimated at < 2 % by volume, below the detection limit of X-ray diffraction. By fabricating textured BFCf, it can be shown that the observed ferromagnetic response is dominated by the secondary phase; although the material is textured, the magnetic response is anisotropic, proving that the BFCT matrix is not ferromagnetic. The templated grain growth techniq ue was used to synthesis textured 60BiFeO-40PbTiO or 60:40BFPT. Both Aurivillius templates (Bi4 Ti30 12 and PbBi4Ti40) and perovskite templates (BaTiO), SrTi03 and 0.4(NaI2BiIl2)Ti03-0.6PbTi03) were used to prepare 60:40BFPT. Only BaTiO) templates were successful in imparting texture on the BFPT matrix. In the case of SrTiO, a reduction in Curie temperature was observed (Tc = 350°C) due to the substitution of Sr+. Aurivillius templates resulted in high Curie temperatures (610 °C). However, the resulting ceramics show low remanent polarization, while SrTi03 and BaTi03 templated ceramics show higher remanent polarizations of36 and 30 llc/cm2 , respectively. There are many repolts in the literature describing the effect of texture on the magnetic and electric properties of materials. Texture is used to provide an enhancement in various properties, compared to random orientation, for example an increase in piezoelectric coefficien t, or remnant magnetization. In this work, molten salt and tape casting techniques were employed to synthesis textured bismuth ferrite based ceramics. The fabrication of highly-oriented polycrystalJine ceramics of Bi5Feo.SCOo.5 Ti JOl5 (BFCT), prepared via molten salt synthesis and uniax ial pressing of high aspect ratio pl atelets is reported. Electron backscatter images show a secondary phase within the ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from scanning electron microscopy was estimated at < 2 % by volume, below the detection limit of X-ray diffraction. By fabricating textured BFCf, it can be shown that the observed ferromagnetic response is dominated by the secondary phase; although the material is textured, the magnetic response is anisotropic, proving that the BFCT matrix is not ferromagnetic. The templated grain growth techniq ue was used to synthesis textured 60BiFeOJ-40PbTiOJ or 60:40BFPT. Both Aurivillius templates (Bi4 Ti30 12 and PbBi4 Ti40 IS) and perovskite templates (BaTiO), SrTi03 and 0.4(NaII2BiIl2)Ti03-0.6PbTi03) were used to prepare 60:40BFPT. Only BaTiO) templates were successful in imparting texture on the BFPT matrix. In the case of SrTiOJ, a reduction in Curie temperature was observed (Tc = 350°C) due to the substitution of Sr+. Aurivillius templates resulted in high Curie temperatures (610 °C). However, the resulting ceramics show low remanent polarization, while SrTi03 and BaTi03 templated ceramics show higher remanent polarizations of36 and 30 llc/cm2 , respectively. Synchrorron measurements clearly show textured 6O:40BFPT using BaTi03 templates. Polari sation and strain field measurements were used to show that the resulting material wa<; ferroelectric, with a Ec of 6 kV/mm, a Pr of 30 llClcm2 and a total strain of 0.09%. Vibrating sample magnetometry was used, and showed magnetic anisotropy in the material fabricated using BaTiOJ templates. The coercive field of 177 Oe and maximum magnetization of 1.43 emu/g was obtained when magnetic field applied nonna] to the cast direction. By applying the magnetic field along (0 the cast direction, a far higher coercive field of 908 Oe, and lower maximum magnetization of 0.29 emu/g was reali zed. The reaction of Ba with the BFPT matrix leads to the generation of ferromagnetic ordering, as opposed to the anti ferromagnetic ordering observed in BFPT prepared using conventional processing. In summary, the template grain growth technique has been used to generate textured Ba-doped BFPT. The resulting materia] is both ferrom agnetic and ferroelectric at room temperature.