直流偏置电场下BaTiO_3基陶瓷介电常数非线性机理的研究

Mechanism of nonlinear dielectric constant of BaTiO_3-based ceramics under high DC electric field

采用传统固相法制备了Ba0·6Sr0·4TiO3(BST)和BaZrxTi1-xO3(x=0·25,0·3,0·35,0·4)(BZT)陶瓷,并对其在直流偏置电场下的介电常数非线性行为进行了系统、详细的研究.结果表明,基于Devonshire的宏观相变理论(phenomenologicaltheory)提出的公式εεr(r(ap0p))=[1+αε13r(0)E2]1/3和ε(E)=ε1-ε2E2+ε3E4,均可定量地解释BST体系顺电相的介电常数非线性行为,其中εr(app)表示材料在电场下的介电常数,εr(0)表示不加电场即静态下材料的介电常数,α是非谐性因子,E表示电场强度,ε(E)表示材料在电场下的介电常数,ε1,ε2,ε3分别表示线性、非线性和高阶介电常数.而对于处于铁电相和居里温度附近的BST体系,则需要考虑铁电畴对介电常数非线性的贡献,这种贡献随着外加直流偏置电场强度的增大逐步减小.对于弛豫铁电体BZT体系,即使处于顺电相,也必须考虑由极性微区的冻结与合并引起的介电常数的下降,极性微区对介电常数非线性的贡献随着电场强度和温度的上升而有所下降.

Ba0.6 Sr0.4 TiO3 （BST） and Ba （ Zrx Ti1-x） O3 （BZT） （ x = 0.25,0.3,0.35,0.4 ） ceramics were prepared by traditional ceramic processing and their structural, dielectric properties as well as the mechanism of its nonlinear dielectric constant under de electric field were systemically examined. The results show that the phenomenological theory of Devonshire can be applied to BSTsystem when the material is in the paraelectric state, and the equations εr（app）/εr（0）=1/[1＋αεr（0）E^2]^1/3和ε（E）=ε1-ε2E^2＋ε3E^4 can give a quantitative explaination of its nonlinear dielectric behavior under high DC electric field, where εr（0） and εr（app） are the dielectric constants under zero DC field and under the applied field respectively, α is the anharmonie eoefficeient, E is the strength of electric field, ε （F） is the dielectric constant under the applied field and ε1 , ε2, ε3 is linear, nonlinear and high order dielectric constant respectively. When the BST system is in the ferroeleetrie or phase transition state, the domain and domain wall＇s extrinsic contributions to the nonlinear dielectric constant cannot be neglected, and the extrinsic contributions decrease with the increase of the strength of the electric field. For the relaxor-like BZT system, even if it is in paraeleetrie state, the extrinsic contribution of polar mieroregions to the nonlinear dielectric constant can be markedly observed. With the increase of the strength of the electric field and temperature, this contribution decreases.