Pressure-induced abnormal ionic-polaronic-ionic transition sequences in AgBr.
Pressure-induced abnormal ionic-polaronic-ionic transition sequences in AgBr.
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DOI：
10.1039/c7cp07830g
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发表时间：
2018-03
期刊：
影响因子：
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通讯作者：
Jia Wang;Yonghao Han;Hao Liu;Guozhao Zhang;Cailong Liu;C. Gao
中科院分区：
文献类型：
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作者：
Jia Wang;Yonghao Han;Hao Liu;Guozhao Zhang;Cailong Liu;C. Gao
通过电化学阻抗谱测量和第一性原理计算，系统地研究了超离子导体AgBr在高达30.0 GPa高压下的电输运行为。从阻抗谱测量中，发现了压力诱导的异常离子-极化子-离子跃迁。在此，在没有结构相变的情况下，离子在5.0 GPa下发生极性转变。在8.6 GPa下，AgBr的离子态经过结构相变后被重新激活。以往基于x射线衍射数据的结构研究并不能提供强有力的证据来支持5.0 GPa下AgBr中的离子-极极性跃迁。本文基于第一性原理计算，提出了一个局域电子汤模型来解释离子-极极性跃迁的物理起源。在该模型中，Br原子周围更多的局域电子被压入间隙空间，同时，银离子和局域电子背景在5.0 GPa下形成极化子。因此，局域电子背景从平衡位置的移动有效地屏蔽了Ag+离子的扩散，就像豆子完全被困在一杯浓汤里一样。
The electrical transport behavior of the superionic conductor AgBr was systematically studied under high pressure up to 30.0 GPa with electrochemical impedance spectra measurements and first-principles calculations. From impedance spectra measurements, a pressure-induced abnormal ionic-polaronic-ionic transition was found. Herein, the ionic to polaronic transition at 5.0 GPa occurs with the absence of a structural phase transition. At 8.6 GPa, the ionic state of AgBr can be reactivated after a structural phase transition. Previous structural studies based on X-ray diffraction data cannot provide strong evidence to support the ionic-polaronic transition in AgBr at 5.0 GPa. In this paper, based on first-principles calculations, a localized-electron-soup model was proposed to explain the physical origin of the ionic-polaronic transition. In this model, more localized electrons around the Br atoms are pressed into interstitial spaces and, simultaneously, polarons are formed between Ag+ ions and the localized electron background at 5.0 GPa. Therefore, the diffusion of Ag+ ions is effectively screened by the movement of the localized electron background from its equilibrium position, much like beans completely trapped in a cup of thick soup.