Stacking Disorder by Design: Factors Governing the Polytypism of Silver Iodide upon Precipitation and Formation from the Superionic Phase
Stacking Disorder by Design: Factors Governing the Polytypism of Silver Iodide upon Precipitation and Formation from the Superionic Phase
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DOI：
10.1021/acs.cgd.8b01715
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发表时间：
2018-11
影响因子：
3.8
通讯作者：
Rachael L. Smith;M. Vickers;Martin Rosillo-Lopez;C. Salzmann
中科院分区：
文献类型：
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作者：
Rachael L. Smith;M. Vickers;Martin Rosillo-Lopez;C. Salzmann
碘化银（AgI）用于从荧光和抗菌涂层到摄影和冰成核的广泛应用。通过拟合粉末X射线衍射图与DIFFaX，我们表明，碘化银显示出强烈的倾向，形成堆叠无序材料。其多型性由沉淀过程中银阳离子与碘化物的摩尔比决定。在碘化物丰富的条件下，获得完全六方的b-AgI，而在银阳离子丰富的制度中，在1：2的摩尔比下获得80%的立方堆积的最大百分比。这些研究结果的基础上解释的浓度依赖性的竞争动力学和vacrically-favored吸附过程。此外，以前报道的记忆效应后观察到的转换六方和立方碘化银的高温超离子相和背部现在定量。我们建议，记忆效应起源于过量的离子在碘化银晶体的表面，稳定与六方堆积的碘化银热电。通过调节沉淀条件来“设计”碘化银的多型性的能力提供了第一个例子，其中可以以连续的方式控制材料的堆积无序。未来的研究将阐明这种设计原则是否也可以应用于其他材料。
Silver iodide (AgI) is used for a wide range of applications from photocatalysis and antimicrobial coatings to photography and ice nucleation. By fitting powder X-ray diffraction patterns with DIFFaX, we show that AgI displays a strong tendency to form stacking-disordered materials. Its polytypism is determined by the silver cation to iodide molar ratio during precipitation. Under iodide-rich conditions, fully hexagonal b-AgI is obtained whereas a maximal percentage of cubic stacking of 80% is obtained at a 1:2 molar ratio in the silver cation-rich regime. These findings are explained on the basis of a concentration-dependent competition between kinetically and thermodynamically-favored adsorption processes. Furthermore, the previously reported memory effects observed upon transforming hexagonal and cubic AgI to the high-temperature superionic phase and back are now followed quantitatively. We propose that the memory effects originate from excess ions at the surfaces of AgI crystals that stabilize the pyroelectricity of AgI associated with hexagonal stacking. The ability to ‘design’ the polytypism of AgI by tuning the precipitation conditions provides a first example where the stacking disorder of a material can be controlled in a continuous fashion. Future studies will clarify if this design principle can be applied to other materials as well.