Theoretical investigation of the pure and Zn-doped α and δ phases of Bi 2 O 3
Theoretical investigation of the pure and Zn-doped α and δ phases of Bi 2 O 3
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DOI：
10.1103/physrevb.65.205122
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发表时间：
2002-05
影响因子：
3.7
通讯作者：
J. Carlsson;B. Hellsing;H. S. Domingos;P. Bristowe
中科院分区：
文献类型：
--
作者：
J. Carlsson;B. Hellsing;H. S. Domingos;P. Bristowe
我们用第一性原理计算方法研究了纯和掺锌相的原子和电子结构以及相的原子和电子结构。对于单斜晶系的纯α相，实验和计算的结构参数符合得很好，另外，计算的价带和光学带隙中的态密度与光电子能谱有很好的关联。对于具有缺陷萤石结构的纯β相，计算表明，在三种可能的氧空位结构中，$<100>$-空位有序化是首选。然而，这个相必须被认为是在$T=0\mathm{K}$时的过冷相，因为我们发现单个位移的空位(即偏离$<100>$有序的空位)可以触发$\ensureath{\Delta}$-$\ensureath{\α}$相变。类似地，相中的锌替代杂质也可以触发这一相变。锌杂质在α相中的形成能为1.34 eV，从而在$T=1000mathm{K}处产生最大杂质浓度$7.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\mathm{at}.%$zn。锌在$\mathm{Bi}_{2}{\mathm{O}}_{3}相中的低溶解度与观察到的氧化锌与{mathrm{Bi}_{2}{\mathm{O}}_{3}的相分离一致。
We have studied the atomic and electronic structure of pure and Zn-doped $\ensuremath{\alpha}$ and $\ensuremath{\delta}$ phases of ${\mathrm{Bi}}_{2}{\mathrm{O}}_{3}$ by first-principles calculations. For the pure $\ensuremath{\alpha}$ phase which is monoclinic, good agreement was obtained between the experimental and calculated structural parameters and, in addition, the calculated density of states in the valence band and the optical band gap correlated well with photoemission spectra. For the pure $\ensuremath{\delta}$ phase, which has a defective fluorite structure, the calculations suggest that of three possible oxygen vacancy structures, $〈100〉$-vacancy ordering is preferred. This phase, however, must be considered as a supercooled phase at $T=0 \mathrm{K}$ since we found that a single displaced vacancy (i.e., one that deviates from $〈100〉$ ordering) can trigger a $\ensuremath{\delta}$-$\ensuremath{\alpha}$ phase transition. Similarly, a Zn substitutional impurity in the $\ensuremath{\delta}$ phase can also trigger this phase transition. The formation energy of a Zn impurity in the $\ensuremath{\alpha}$ phase was found to be 1.34 eV, resulting in a maximum impurity concentration of $7.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6} \mathrm{at}.%$ Zn at $T=1000 \mathrm{K}.$ The low solubility of Zn in the $\ensuremath{\alpha}$ phase of ${\mathrm{Bi}}_{2}{\mathrm{O}}_{3}$ is consistent with the observed phase separation between ZnO and ${\mathrm{Bi}}_{2}{\mathrm{O}}_{3}.$