氧含量对BiFeOδ多晶陶瓷介电特性的影响

采用固相反应法制备了不同含氧量的BiFeO_δ多晶陶瓷样品，利用HP4294A阻抗分析仪测量了样品的介电特性随频率和氧含量的变化，用正电子湮没寿命谱学的方法研究了样品中因氧含量的变化所引起的结构缺陷. 实验结果表明：引入氧空位和氧填隙离子缺陷都会使介电常数减小，而介电损耗则随氧含量的增加而增加，二者的变化范围均在10%—35%之间；对不同氧含量的BiFeO_δ样品，介电常数和介电损耗随测量频率的增加而减小. 氧空位的引入使得局域电子密度变小，正电子平均寿命τ_m增加. 在氧含量δ=2.99时电子密度最大(n_e=3.90×10²³/cm³)，继续增加氧含量对正电子寿命与局域电子密度的影响不大. BiFeO_δ样品的介电常数和介电损耗随氧含量的变化可以在空间电荷限制电导的框架下来理解.

Effect of oxygen content on the dielectric properties of polycrystalline BiFeOδ ceramics

Multiferroic BiFeO_δ ceramics of various oxygen contents (δ) were prepared by solid state reaction. Frequency dependence of dielectric properties of BiFeO_δ samples at room temperature was measured in the frequency range from 40Hz to 1MHz with a HP4294A precision impedance analyzer. For all the samples, the dielectric constant and loss decrease with measurement frequency. The effect of introducing oxygen vacancy or excess oxygen is to reduce the dielectric constant of BiFeO₃. The dielectric loss in BiFeO_δ increases with oxygen content. The large change (10%—35%) in the dielectric properties of BiFeO₃ samples with various oxygen content(δ) may be understood in terms of the space charge limited conduction associated with crystal defects. The effects of oxygen content on the crystal structure of BiFeO₃　ceramics were also investigated using positron annihilation technique (PAT). It has been found that the mean positron lifetime in BiFeO_δ　is strongly dependent on the oxygen content. Introducing oxygen vacancy leads to an increase in positron lifetime and a decrease in local electron density of BiFeO₃ ceramics.