Research On The Preparation Method Of SrTiO₃ Voltage-sensitive Ceramic

SrTiO₃-series capacitor-varistor ceramics, a kind of important voltage-sensitive ceramic materials with double functions, have low breakdown voltage, excellent nonlinear coefficient, high dielectric constant and low dielectric loss. They belong to multifunctional ceramics (MFC) and have characteristics of high frequency noise absorption, burst pulse absorption, surge absorption and self-recovery. SrTiO₃ varistors have been widely used as transient high-voltage protector and surge arrestor in the field of low voltage, such as restraining the noise of micro direct-current machine or source input, protecting the switch of inductive load or silicon controlled rectifier transwitch, and by-pass capacitors.The experiment contains SrTiO₃ power's production method, adulteration, formation, and technology of fire method. And the concrete content consists of following parts:(1) Synthesizing SrTiO₃ powder in hydro thermally. In the high pressure responds container, Sr(NO₃)₂ and Ti(OC₄H₉)₄ as raw material, NaOH as mineralizer, ethanol and aquoion as medium, SrTiO₃ powder with the grain size about 100nm can be synthesized. SEM of samples indicates that the powder 'grain size is even, but still exists some reunion.(2) Powder's adulteration. Except the tradition physical mixture adulteration, the hydro thermally synthesize method has been attempt in the experiment. The XRD indicates that La³⁺and Cu²⁺ succeed in being added to the SrTiO₃ powder.(3) Powder's formation. The result of the ceramics' density indicates that the cold isostatic pressing method is much better than the dry pressing method.(4) Technology of fire method. At the present, SrTiO₃ ceramic varistor is often prepared by the single-fired method. During the production, reducing atmosphere is created by H₂. But H₂ can bring about big danger. To avoid this sequent, N₂ and graphite are adopted to create reducing atmosphere in the experiment. (5) SrTiO₃ ceramic varistor with La₂O₃ and Nb₂O₅ as donor element has the properties that varistor voltage is 18V, nonlinear coefficient is 4.6, relative dielectric constant is 2.7×10⁴, dielectric loss 0.078.