Prepapration Of Textured Niobate Based Ceramics

Because strontium barium niobate (Sr_xBa_1-xNb₂O₆ SBN) crystal, with tungsten bronze structures, have large pyroelectric and linear electro-optic coefficients, as well as strong photo refractive effects, it has been widely used in the optical devices. (001) SBN textured ceramics with properties closed to single crystal values would be advantageous due to their ease of fabrication and shaping, thermal and stress resistance, and cost-effectiveness.In this paper, strontium barium niobate (SBN)-based ceramics were selected as the experimental system. Textured SBN ceramics, using SBN crystal as template, were fabricated by Reactive Template Grain Growth (RTGG) and Template Grain Growth (TGG) technique. Meanwhile, the following researches had been done: The sintering behavior and structures evolution of SBN, effects of precursors on structures evolution and the mechanism of abnormal grain growth of SBN ceramics had been investigated; Effects of processing parameters and precursors on the microstructure of SBN crystal and the mechanism of the growth of SBN crystal synthesized by molten salt method were studied. Effects of processing parameters, such as the content of template, the matrix selection, and sintering temp and time, had been investigated. The main results of this thesis are as follows:(1) Through the investigation of the sintering process of SBN ceramics with different content of Sr and pre-sintered at 1200℃, we confirmed that the development of the liquid phase which might be due to the existent of SN is the reason of abnormal grain growth. Pretreatment at or higher than the complete formation temperature of SBN could prevent the abnormal grain growth(2) Sr_0.7Ba_0.3Nb₂O₆ ceramics (SBN70) were prepared by using conventional sintering techniques from nitrate precursor and carbonate precursor. SBN70 from nitrate precursors showed a duplex microstructure. Abnormal grain growth occurs more easily than SBN70 from carbonate precursors.(3) The purely acicular Sr_0.5Ba_0.5Nb₂O₆ (SBN50) particles were prepared by both carbonate precursor and nitrate precursor. The morphology of SBN50 may be attributed to the content and morphology of SrNb₂O₆ particles phase which were different by different precursors at the melting point of KCl. The growth mechanism of SBN50 particles was interpreted as two-dimensional nucleation.(4) Effects of processing parameters, such as the content of template, the matrix selection, and sintering temp and time, had been investigated; Texture fracture of SBN ceramic, sintered at 1325℃ for 10h, was about 72% in (001) direction.