Phase Behavior and Superionic Transport Characteristics of (M x Rb 1–x ) 3 H(SeO 4 ) 2 (M = K or Cs) Solid Solutions
Phase Behavior and Superionic Transport Characteristics of (M x Rb 1–x ) 3 H(SeO 4 ) 2 (M = K or Cs) Solid Solutions
复制标题
(M x Rb 1-x ) 3 H(SeO 4 ) 2 (M = K 或 Cs) 固溶体的相行为和超离子输运特性
DOI：
10.1021/acs.chemmater.9b03856
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发表时间：
2019
影响因子：
8.6
通讯作者：
Haile, Sossina M.
中科院分区：
文献类型：
--
作者：
Yi, Dezhi;Sanghvi, Sheel;Kowalski, Chatr Panithipongwut;Haile, Sossina M.
其中M是碱性离子，其中M是碱性离子，由于从单斜晶系转变为具有动力学无序氢键网络的超质子三角相而导致的电导率显著增加，这类固体酸硒盐引起了人们的注意。这一类中的三个特定成员K3H(SeO4)2、Rb3H(SeO4)2和Cs3H(SeO4)2之间的显著相似之处使末端成员之间的伪二元系统成为探索驱动超质子跃迁和控制电导率大小的晶体化学特征的理想选择。因此，本文采用原位高温衍射法和交流阻抗谱对(KxRb1-x)3H(SeO4)2和(CsxRb1-x)3H(SeO4)2体系进行了系统的研究。在整个组成范围内，观察到了向空间群R3̅错位的超质子相转变。随着碱性阳离子平均尺寸的减小，超质子转变温度普遍降低，而对于给定的温度，电导率单调增加。根据应变对单斜相内能的可能影响，讨论了转变温度随成分的变化。超质子相的电导率服从唯象补偿规律，指数前项的对数与激活能线性相关。质子传输活化能随平均阳离子尺寸的减小暂定归因于氢键长度的收缩，推测是由于晶胞体积的收缩。在特殊组成Cs2RbH(SeO4)2处，结构和电导率发生了细微的变化，对应于Cs和Rb物种可以在可用的阳离子位置上完全不混合的结构。虽然没有观察到阳离子的完全有序排列，但在高温相和低温相以及两种化学体系中，较大的阳离子优先占据两个阳离子中较大的一个。
Solid acid selenates in the class M3H(SeO4)2, in which M is an alkali ion, have garnered attention as a result of the dramatic increase in conductivity that occurs upon transition from a monoclinic to a superprotonic trigonal phase with a dynamically disordered hydrogen-bond network. The significant similarities between three specific members of this class, K3H(SeO4)2, Rb3H(SeO4)2, and Cs3H(SeO4)2, render the pseudobinary systems between end-members ideal for an exploration of the crystal chemical features that drive the superprotonic transition and control the magnitude of the conductivity. Accordingly, a systematic study of the (KxRb1–x)3H(SeO4)2and (CsxRb1–x)3H(SeO4)2systems is carried out here using in situ high-temperature diffraction and conductivity measurements by ac impedance spectroscopy. Across the entire composition range, a transition to a superprotonic phase of the space groupR3̅mis observed. With decreasing average size of the alkali cation, the superprotonic transition temperature generally decreases and, for a given temperature, the conductivity monotonically increases. The variation in transition temperature with composition is discussed in terms of possible strain effects on the internal energy of the monoclinic phase. The conductivity in the superprotonic phase is found to obey the phenomenological compensation rule, in which the logarithm of the pre-exponential term is linearly correlated with the activation energy. The decrease in activation energy for proton transport with decreasing average cation size is tentatively ascribed to a contraction in the length of the hydrogen bonds, presumed from the contraction of the cell volume. Subtle changes in structure and conductivity occur at the special composition Cs2RbH(SeO4)2, corresponding to a structure in which Cs and Rb species could be fully unmixed over available cation sites. While a fully ordered arrangement of cations was not observed, the larger cation was found to preferentially occupy the larger of the two cation sites in both high- and low-temperature phases and in both chemical systems.