High temperature phase transformations and Superprotonic conductivity in Cs2(HSeO4)(H2PO4)

IF 3 4区 材料科学 Q3 CHEMISTRY, PHYSICAL
Grace Xiong , Ara Jo , Louis S. Wang , Sossina M. Haile
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引用次数: 0

Abstract

The compound Cs2(HSeO4)(H2PO4) is of interest due to its high conductivity in its superprotonic state. In the present work, in situ X-ray diffraction studies, simultaneous thermal analysis, and AC impedance spectroscopy, each performed under controlled value of steam partial pressure (pH2O), were carried out to elucidate the crystallographic features of the transformation and resolve the conductivity in the high temperature phase. The studies reveal that the material transforms to a cubic phase at a temperature of approximately 116 °C, that the activation energy for proton transport in the cubic phase is 0.304(2) eV, and the magnitude of the conductivity is comparable to that of Cs2(HSO4)(H2PO4). Despite differences in the room temperature structures of Cs2(HSeO4)(H2PO4), Cs2(HSO4)(H2PO4), and CsH2PO4, each has a monoclinic to cubic transformation entropy of approximately 23 J/mol(CsHxXO4)/K. Under pH2O = 0.05 atm, the cubic phase of Cs2(HSeO4)(H2PO4) is stable to approximately 250 °C. Under elevated pH2O (0.3 atm), exsolution of a trigonal phase, with structure analogous to that of Cs3H(SeO4)2, was found to accompany the transformation to the cubic phase. While the driver for this transformation is not fully known, the cell volumes of both the exsolved and matrix phases indicate they are chemically distinct, respectively, from Cs3H(SeO4)2 and Cs2(HSeO4)(H2PO4), suggesting additional chemical levers for control of transformation behavior.

Cs2(HSeO4)(H2PO4)中的高温相变和超质子电导率
Cs2(HSeO4)(H2PO4)化合物因其超质子态的高导电性而备受关注。本研究在蒸汽分压(pH2O)受控的条件下,分别进行了原位 X 射线衍射研究、同步热分析和交流阻抗光谱分析,以阐明转变的晶体学特征并解析高温相的导电性。研究发现,该材料在温度约为 116 ℃ 时转变为立方相,立方相中质子传输的活化能为 0.304(2) eV,电导率的大小与 Cs2(HSO4)(H2PO4)相当。尽管 Cs2(HSeO4)(H2PO4)、Cs2(HSO4)(H2PO4) 和 CsH2PO4 的室温结构不同,但它们从单斜到立方的转化熵均约为 23 J/mol(CsHxXO4)/K。在 pH2O = 0.05 atm 的条件下,Cs2(HSeO4)(H2PO4)的立方相在大约 250 °C 的温度下是稳定的。在 pH2O 升高(0.3 atm)的条件下,发现在向立方相转化的过程中,伴随着三方相的溶解,出现了结构类似于 Cs3H(SeO4)2 的三方相。虽然这种转变的驱动因素尚不完全清楚,但溶出相和基质相的晶胞体积表明,它们在化学上分别不同于 Cs3H(SeO4)2 和 Cs2(HSeO4)(H2PO4),这表明还有其他化学杠杆可以控制转变行为。
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来源期刊
Solid State Ionics
Solid State Ionics 物理-物理:凝聚态物理
CiteScore
6.10
自引率
3.10%
发文量
152
审稿时长
58 days
期刊介绍: This interdisciplinary journal is devoted to the physics, chemistry and materials science of diffusion, mass transport, and reactivity of solids. The major part of each issue is devoted to articles on: (i) physics and chemistry of defects in solids; (ii) reactions in and on solids, e.g. intercalation, corrosion, oxidation, sintering; (iii) ion transport measurements, mechanisms and theory; (iv) solid state electrochemistry; (v) ionically-electronically mixed conducting solids. Related technological applications are also included, provided their characteristics are interpreted in terms of the basic solid state properties. Review papers and relevant symposium proceedings are welcome.
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