Empirical Evidence for A-Site Order in Perovskites
Empirical Evidence for A-Site Order in Perovskites
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DOI：
10.1111/jace.14547
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发表时间：
2017
影响因子：
3.9
通讯作者：
K. Tolman;R. Ubic;Bing Liu;I. Williamson;K. Bedke;Eric B. Nelson;Lan Li;X. Chen
中科院分区：
文献类型：
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作者：
K. Tolman;R. Ubic;Bing Liu;I. Williamson;K. Bedke;Eric B. Nelson;Lan Li;X. Chen
组成-结构关系的模型在实验室和工业中都是有用的，但很少存在含钙钛矿的外部缺陷或阳离子有序。在这项工作中，一个经验模型被用来预测存在的A-网站阳离子有序。具体地，使用常规固态混合氧化物方法合成Na（1 - 3x）/2La（1 + x）/2TiO 3系统中的四种组成（x = 0.0、0.0533、0.1733和0.225）。x = 0端元（Na0.5La0.5TiO3）的结构已经在各种空间群中报道，但总是在A位上随机分布Na+和La3 +;然而，经验模型表明，它不仅是有序的，而且伴随着有序过程的小体积增加。虽然通过X射线或中子衍射在该组合物中没有观察到长程A位有序的证据，但电子衍射数据表明Na+和La 3+离子的短程有序，随着x的增加，阳离子有序度降低（但有序域的规模和空位有序度通常增加）。通过密度泛函理论的第一性原理计算支持这两个结论，短程有序在Na0.5La0.5TiO 3是稳定的，它导致相对于无序的类似物的体积增加。对Li（1 - 3x）/2La（1 + x）/2TiO 3和Na（1 - 3x）/2La（1 + x）/2（Mg0.5W0.5）O3固溶体进行了类似的分析。这些系统提供了额外的验证所使用的经验建模方法的准确性和通用性。
Models for composition–structure relationships are useful in both the lab and industry, yet few exist for perovskites-containing extrinsic defects or cation ordering. In this work, an empirical model is used to predict the existence of A-site cation ordering. Specifically, four compositions in the Na(1−3x)/2La(1+x)/2TiO3 system (x = 0.0, 0.0533, 0.1733 and 0.225) were synthesized using a conventional solid-state mixed-oxide method. The structure of the x = 0 end-member (Na0.5La0.5TiO3) has been reported in various space groups, but always with a random distribution of Na+ and La3+ on the A site; however, empirical modeling suggests that it is not only ordered but also that a small volume increase accompanies the ordering process. While no evidence of long-range A-site ordering is observed in this composition via X-ray or neutron diffraction, electron-diffraction data indicate short-range ordering of Na+ and La3+ ions, with the degree of cation ordering decreasing (but the scale of ordered domains and degree of vacancy ordering generally increasing) with increasing x. First-principles calculations via density functional theory support both conclusions that short-range ordering in Na0.5La0.5TiO3 is stable and that it results in a volume increase with respect to the disordered analog. A similar analysis has been conducted for the Li(1−3x)/2La(1+x)/2TiO3 and Na(1−3x)/2La(1+x)/2(Mg0.5W0.5)O3 solid solutions. These systems provide additional validation of the accuracy and versatility of the empirical modeling method used.