Multiferroic Properties Of Sol-gel Derived(Bi_0.5Na_0.5)TiO3Based Ceramics And Thin Films

(Bi0.5Na0.5)TiO3(abbreviated as BNT) is a complex ferroelectric perovskite-structure compounds with two different ions at the A site of the ABO3structure first discovered by Smolensky et al. As a kind of extremely important basic material, functional ceramics have been found its application throughout every field of human lives. Traditional PZT-based ceramics have been widely used for the sake of excellent properties and mature manufacturing process. BaTiO3(abbreviated as BT) and BNT have gotten much attention because of their excellent electrical properties.The (1-x)(Bi0.5Na0.5)TiO3-xBaTiO3(x=0.06, abbreviated as BNT-6BT) powder and ceramic was synthesized by sol-gel process. The phase structure and dielectric properties of the ceramics were investigated. The ceramic was sintering at1000-1100℃for2-4h in air atmosphere, and the X-ray diffraction (XRD) results revealed that the samples was pure perovskite-type phase. The Curite temperature of BNT-6BT ceramics was high up to348℃. The temperature dependence of dielectric permittivity and loss revealed there were two phase transitions, which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic) in BNT-6BT ceramics. Diffuse phase transitions were observed in BNT and BNT-6BT ceramics and the Curie-Weiss Exponent (CWE) were nearly2. BNT-6BT after annealing at1050℃were reheated in vacuum at1050℃for120min measured at room-temperature. Ferromagnetism at room-temperature was observed in these samples. The ferroelectric was stronger than BNT-6BT ceramics after annealing at1050℃were reheated in vacuum. The temperature dependence of εr of poled BNT-6BT ceramics after annealing at1050℃were reheated in vacuum under various measuring frequencies (1,2,3,5,10,20,30,50, and100kHz).The BNT-6BT ceramic was synthesized by sol-gel process. The dielectric properties, ferromagnetism properties and ferroelectric properties of the ceramics were investigated. Sintering was made at1050℃for2h in air atmosphere, then reheated in vacuum at1050℃for120min. The Curite temperature of BNT-6BT ceramics was high up to373℃. The temperature dependence of dielectric permittivity revealed there were two phase transitions, which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic) in BNT-6BT ceramics. The vacuum annealing enhances ferromagnetism (FM), while the subsequent air-annealing lowers FM again, indicating that the observed FM may be connected with the oxygen vacancies. It is the first time to discover the ferromagnetism properties in BNT-6BT ceramics. Good coexistence of ferromagnetic and ferroelectric behaviors at room temperature for BNT-6BT ceramics after annealing at1050℃were reheated in vacuum at1050℃for120min. It can be expected that for the multiferroics with ferromagnetic and ferroelectric ordering simultaneously, the coupling between the magnetic and electric properties will lead to the magnetoelectric (ME) effect.The Bi4Ti3O12film was synthesized by sol-gel process, and annealed at650℃for10min in air atmosphere. The dielectric properties, ferromagnetism properties and ferroelectric properties of the films were investigated. The results shown that Bi4Ti3O12thin film could exhibit weak room-temperature ferromagnetism (FM). It is the first time to discover the ferromagnetism properties in Bi4Ti3O12thin film. The coexistence of ferromagnetism (FM) and ferroelectricity (FE) at room temperature was observed in Bi4Ti3O12films with an annealing temperature of650℃for10min in air atmosphere. The typical small signal dielectric constant and dissipation factor of the film at a frequency of100Hz were about100and0.05, respectively. It can be expected that for the multiferroics with ferromagnetic and ferroelectric ordering simultaneously, the coupling between the magnetic and electric properties will lead to the magnetoelectric (ME) effect.