铋层状共生结构铁电体Bi7Ti4NbO21具有天然的超晶格结构.采用基于密度泛函(DFT)的第一性原理计算对Bi7Ti4NbO21及其相关化合物进行了研究.计算得到Bi7Ti4NbO21的生成焓为-56.21 eV,带隙为0.796 eV,而对于组成单元Bi3TiNbO9和Bi4Ti3O12,生成焓分别为-30.72和-43.32 eV,带隙分别为2.535和2.436 eV.分析表明,共生结构Bi7Ti4NbO21相对于同组分的组成单元处于热力学亚稳态,其钙钛矿层是电子电导的主要影响因素,带隙相对于组成单元减小也是源于钙钛矿层的导带底的下移.
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