DEFECT AGGREGATION IN ANION-EXCESS FLUORITES - DOPANT MONOMERS AND DIMERS
DEFECT AGGREGATION IN ANION-EXCESS FLUORITES - DOPANT MONOMERS AND DIMERS
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DOI：
10.1103/physrevb.25.6425
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发表时间：
1982-01-01
影响因子：
3.7
通讯作者：
ONG, SH
中科院分区：
文献类型：
--
作者：
CORISH, J;CATLOW, CRA;ONG, SH
本文对Ca F 2 、Sr F 2 和Ba F 2 三种萤石中取代三价阳离子杂质和间隙氟离子的小团簇的稳定性进行了理论检验。计算了各种团簇的能量并检验了团簇的稳定性；特别令人感兴趣的是它们捕获或丢失插页式广告的能力以及改变方向的能力。我们发现，在Ca F 2 中，最近邻（NN）C 4 v 复合体M s 3+ F i−（s 表示替代，i 表示间隙）更稳定，而在Ba F 2 中，下一个NN（NNN）C 3 v 复合体更稳定；在Sr F 2 中，NN 和NNN 配合物具有相当的稳定性。通过在NN晶格F-离子的相反<111>方向上的弛豫，确认了包含两个M s 3+ 和两个F i- 的NN二聚体簇的稳定性。 F i− 离子位于 NNN 而不是 NN 位置的二聚体与 NN 二聚体具有相当的稳定性，因此可能是在 NNN 单体受到青睐时形成的。与单体一样，二聚体可以通过解离失去 F i− ，因此可能有助于电荷传输过程。 NN 二聚体可以非常方便地捕获游离的 F− 间质；在 Ca F 2 中，即使这些间隙必须来自二聚体本身，情况也是如此。在 Ca F 2 和 Sr F 2 中，NN 二聚体可以从 NN 单体中获取 F i−。我们尽可能将理论结果与实验数据进行比较。在数据可用的每种情况下，我们关于簇稳定性的结果总体上与实验定性一致。因此，令人惊讶的是，计算出的偶极取向活化能通常过高约 0.2 eV，而我们无法找到这种差异的根源；然而，这似乎与 M s 3+ F i− 势不相符。
This paper is concerned with a theoretical examination of the stability of small clusters of substitutional trivalent cation impurities and interstitial fluoride ions in the three fluorites Ca F 2, Sr F 2, and Ba F 2. The energies of a variety of clusters have been calculated and the stability of the clusters examined; of particular interest is their ability to trap or lose interstitials and their ability to change their orientation. We find that in Ca F 2 the nearest-neighbor (NN) C 4 v complex M s 3+ F i−(s denotes substitutional, i denotes interstitial) is more stable, whereas in Ba F 2 it is the next-NN (NNN) C 3 v complex that is more stable; in Sr F 2 the NN and NNN complexes have comparable stability. The stabilization of NN dimer clusters containing two M s 3+ and two F i− by the relaxation in opposite< 111> directions of NN lattice F− ions is confirmed. Dimers in which the F i− ions are in NNN rather than NN positions have comparable stability to the NN dimers and so are presumably formed when it is the NNN monomer that is favored. Like the monomers, the dimers can lose F i− by dissociation and so may contribute to charge-transport processes. The NN dimer can trap free F− interstitials with remarkable facility; in Ca F 2 this is so even when these interstitials must come from the dimers themselves. In both Ca F 2 and Sr F 2 the NN dimers can take F i− from NN monomers. Wherever possible our theoretical results have been compared with experimental data. Our results on the stability of clusters are in general qualitative agreement with experiment in every case where data are available. It is perhaps surprising, therefore, that the calculated activation energies for dipolar orientation are generally too high by about 0.2 eV and we have been unable to find the origin of this discrepancy; it seems, however, not to lie with the M s 3+ F i− potentials.