杂化非本征铁电体Ca2.94Na0.06Mn2O7中异常的带隙变化

Abnormal variation of band gap in hybrid improper ferroelectricity Ca2.94Na0.06Mn2O7

为了研究杂化非本征铁电体Ca3Mn2O7(CMO)的带隙变化,采用标准固相反应法合成了Ca3Mn2O7和Ca2.94Na0.06Mn2O7陶瓷.利用X线衍射仪、X线光电子能谱和紫外-可见光谱分别研究了材料的结构信息、元素价态和带隙.研究结果表明:在Ca2.94Na0.06Mn2O7中氧空位相对于未掺杂的Ca3Mn2O7样品明显减少,且Ca2.94Na0.06Mn2O7的光学带隙值也小于Ca3Mn2O7的带隙值.为了解释这一反常的现象,在分析Mn-O1-Mn键角和Mn/O键各向异性导致的结构对称性的基础上研究了占据带和非占据带的带宽.结果表明增强的结构对称性能够增加占据带和非占据带的带宽,从而减小Ca2.94Na0.06Mn2O7的带隙值.

In order to study the changes of band gap in hybrid improper ferroelectricity Ca3Mn2O7(CMO),Ca3Mn2O7 and Ca2.94Na0.06Mn2O7 ceramics were synthesized by standard solid reaction method.The structural information,elemental valence and band gap of the materials were studied by X-ray diffractometer,X-ray photoelectron spectroscopy and UV-VIS.The results show that the oxygen vacancy in Ca2.94Na0.06Mn2O7 is significantly reduced compared with that in Ca3Mn2O7 sample.The optical band gap value of Ca2.94Na0.06Mn2O7 is also narrower than that of the Ca3Mn2O7.In order to explain this abnormal phenomenon,the bandwidth of occupied and non-occupied bands was studied by analyzing the structural symmetry change caused by Mn-O1-Mn bond angle and Mn-O bond anisotropy.The result shows that the enhanced structural symmetry can increase the bandwidth of occupied and non-occupied bands,thus reducing the band gap value of Ca2.94Na0.06Mn2O7.