Hydrothermal Synthesis Of Na_0.5 Bi_0.5TiO₃-based Nanometer Powders And Studies On Dielectric Properties

Single-crystalline Na_0.5Bi_0.5TiO₃ (NBT) nanowires, with diameters of 100 nm and lengths of about 4μm, were synthesized by using a simple hydrothermal method. Phase composition, morphology and microstructure of the as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The effects of reaction temperature and reaction time on precipitation of the NBT nanowires were investigated. It was found that reaction time significantly influenced the growth behavior of the powders in the hydrothermal system. Based on the experimental results, the one-dimensional (1D) growth mechanism of the NBT was governed by a dissolution-recrystallization mechanism. NBT ceramics derived from the nanowires showed typical characteristics of relaxor ferroelectrics, with diffuseness exponentγof as high as 1.73.K_0.5Bi_0.5TiO₃ (KBT) nanowires have been successfully synthesized by a simple hydrothermal method in KOH solution, which acts as a mineralizer in the hydrothermal process. The KBT nanowires were characterized by XRD and TEM. The results show that KBT nanowires with tetragonal phase have width of 5 nm and length of 200 nm. The as-prepared nanowires were employed to fabricate KBT ceramic by sintering at 1060°C. The specimen exhibits relative dielectric constantεr of 710 and tanδof 0.043 under room temperature at 1 kHz. It was found that the KBT ceramics present typical characteristics of relaxor ferroelectrics.Changing the Ti source, KBT nano-powders have been fabricated by a hydrothermal method. The as-prepared KBT powders were characterized by XRD, IR, SEM and TEM. The effects of KOH concentration and reaction time were investigated. The results show that increasing KOH concentration (4-12M) or extending reaction time would in faver of the formation KBT nano powders. The TEM observation reveals that KBT nano-powders possess a feature of cubic shape and a nano-scale of about 100 nm. The KBT ceramics sintered at 1060℃from hydrothermal powders show compact structure with a small dielectric loss (0.05).(Na_0.82K_0.18)0.5Bi_0.5TiO₃ (NKBT) powders were successfully prepared by the hydrothermal method using NaNO₃, KNO₃, Bi(NO₃)₃·5H₂O and Ti(OC₄H₉)₄ as raw materials and NaOH as mineralizer. The effects of reaction temperature, reaction time and NaOH concentration on precipitation of the NKBT powders were investigated. The prepared NKBT powders were characterized by XRD and SEM. The results show that morphology of the NKBT powders can be controlled by adjusting hydrothermal reaction conditions. The NKBT ceramics with high density can be fabricated from the NKBT powders even by a conventional sintering process.