B替位Ca离子对BaTiO_3铁电相变的影响

用X和射线衍射、透射电镜、扫描电镜、介电性能与电导平衡等方法研究了B位Ca离子对BaTiO_3;陶瓷铁电相变的影响.X射线衍射数据表明,随着B位Ca离子含量的增加(直至5%)c/a比下降至接近1.从介电系数的温度关系可见:含5%B位与6%A位Ca离子的组份其居里峰展宽且下降至室温.发现了当含A位Ca离子(约5%)时,B位Ca离子含量的变化对降低居里点有较显著的作用.据此结果,本文发展了一套热力学模型以解释Ca掺杂BaTiO_3中B位Ca离子对居里峰移动与展宽的作用.

THE EFFECT OF OCTAHEDRALLY-COORDINATED CALCIUM ION ON THE FERROELECTRIC TRANSITION OF BaTiO

The effect of B-site calcium ion on the ferroelectric transition of barium titanate ceramics is investigated by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy, and by the measurements of dielectric properties and equilibrium electric conductivity. The X-ray diffraction data shows that the c/a ratio decreases continuously to near unity with increasing amounts of calcium ion on the B site up to 5%. From the temperature dependence of the dielectric constant it can be seen that the Curie peak is broadened and moves to room temperature for the composition with 5% of Ca ion on B sites and 6% on A sites. It is found that the lowering of the Curie point for a given change in the Ca composltion(0-5%)on B sites is more pronounced when there is Ca(about 50%)on A sites. Based on these results, a thermodynamic model has been developed to explain the mechanism of the Curie peak shifting and the broadening effect caused by the B site Ca ions in Ca-doped barium titanate.