Synthesis, Growth Mechanism And Properties Of Sodium Bismuth Titanate Crystallization Through Hydrothermal Method

Sodium bismuth titanate (Na0.5Bi0.5TiO3,NBT) is a typical A-site complex perovskite (ABO3) ferroelectric, with a relatively high Cuire temperature (Tc=320 ℃), large remanent polarization (Pr=38μC/cm2), and strong ferroelectrics at room temperature, which is considered to be a promising candidate of lead-free piezoelectric ceramics to substitute for lead piezoelectric ceramics. The main research content is comprised of three parts as follow:Nao.sBio.sTiO3powders were successfully prepared by the hydrothermal method using Ti(OC4Hg)4 and Bi(NO3)3·5H2O as raw materials, NaOH as mineralizer. The phase composition and particle morphology of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The reaction temperature, reaction time and the concentration of NaOH were the key points to synthesize NBT powders. The growth kinetics of NBT was evaluated by the JMA equation. When the temperature was in the range of 120℃ to 180℃, the Avrami exponent n decreased. The activation energy of NBT was 50.14KJ·-mol-1.Sodium titanate (Na2Ti3O7) were synthesized by hydrothermal method using Ti(OC4H9)4 and NaOH as raw materials. Then using Na2Ti3O7 and Bi(NO3)3-5H2O as raw materials, NaOH as mineralizer with two-step hydrothermal successfully prepared Na0.5Bi0.5TiO3 powders. Analysis measure resulted that the particles size of Nao.sBio sTiO3 were more uniform, and the crystallinity of Na0.5Bi0.5TiO3 was higher by two-step hydrothermal than one-step hydrothermal. The optimum reaction conditions are as follows:the reaction temperature is 200℃, reaction time 72h and the concentration of NaOH is 14 mol/L.Sodium titanate (Na2Ti3O7) crystal fibers were synthesized by hydrothermal method using TiO2 and NaOH as raw materials. Then using Na2Ti3O7 and Bi(NO3)3·5H2O as raw materials, NaOH as mineralizer with two-step hydrothermal prepared Na0.5Bi0.5TiO3 powders. Analysis measure resulted that the uniformity spherical agglomerates of Na0.5Bi0.5TiO3 were successfully prepared by two-step hydrothermal. The reaction temperature, reaction time and the concentration of NaOH were the key points in this experiment. There are two growth mechanisms in NBT crystalline morphology, one is in situ transformation process, and the other is dissolution and recrystallization mechanism. The prepared powders were compacted at 14MPa and sintered at 1060℃, then the homogenous and compact microstructure of Na0.5Bi0.5TiO3 piezoelectric ceramics was obtained.