Crystal structures and ionic conductivities of ternary derivatives of the silver and copper monohalides -: I.: Superionic phases of stoichiometry MA4I5:RbAg4I5, KAg4I5, and KCu4I5
Crystal structures and ionic conductivities of ternary derivatives of the silver and copper monohalides -: I.: Superionic phases of stoichiometry MA4I5:RbAg4I5, KAg4I5, and KCu4I5
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DOI：
10.1006/jssc.2002.9552
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发表时间：
2002-05-01
影响因子：
3.3
通讯作者：
Berastegui, P
中科院分区：
文献类型：
--
作者：
Hull, S;Keen, DA;Berastegui, P
用粉末中子衍射和复阻抗谱研究了RbAg_4 I_5、KAg_4 I_5和KCu_4 I_5的超离子性质。RbAg 4 I5和KAg 4 I5的室温离子电导率分别为σ = 0.21（6）和0.08（5）Ω（-1）cm（-1），其随着温度的升高而逐渐增加。KCu_4 I_5仅在515（5）K至其熔点605 K之间的温度范围内稳定，其离子电导率在T = 540 K时为σ = 0.61（8）Ω（-1）cm（-1）。在较低的温度下，KCu_4 I_5分解为KI +4 Cu_I，离子电导率福尔斯下降超过三个数量级。室温下RbAg 4 I 5的粉末中子衍射数据的最小二乘修正证实了所报道的结构（空间群P4（1）32，Z = 4，a = 11.23934（3）埃），尽管在移动的Ag+的优选位置上存在一些差异。发现KAg_4 I_5和KCu_4 I_5具有与RbAg_4 I_5相同的基本结构，其中I-形成β-Mn型亚晶格，K+位于畸变八面体环境中，Ag+（Cu+）主要分布在与V四面体配位的两个位置上。利用一种新的最大熵差傅立叶技术来绘制Ag+（Cu+）在晶胞内的分布。(C)2002年爱思唯尔科学（美国）。
The superionic properties of the compounds RbAg4I5, KAg4I5 and KCu4I5, have been investigated by powder neutron diffraction and complex impedance spectroscopy. RbAg4I5 and KAg4I5 have room-temperature ionic conductivities of sigma = 0.21(6) and 0.08(5) Omega(-1) cm(-1), respectively, which increase gradually on increasing temperature. KCu4I5 is only stable in the temperature range between 515(5) K and its melting point of 605 K, and its ionic conductivity is sigma = 0.61(8) Omega(-1) cm(-1), at T = 540 K. At lower temperatures, KCu4I5 disproportionates into KI + 4CuI and the ionic conductivity falls by over three orders of magnitude. Least-squares refinements of the powder neutron diffraction data for RbAg4I5 at ambient temperature confirm the reported structure (space group P4(1)32, Z = 4, a = 11.23934(3) Angstrom), though with some differences in the preferred locations of the mobile Ag+. KAg4I5 and KCu4I5 are found to adopt the same basic structure as RbAg4I5, with the I- forming a beta-Mn-type sublattice, with the K+ located in a distorted octahedral environment and the Ag+(Cu+) predominantly distributed over two sites which are tetrahedrally co-ordinated to V. The implications for the conduction mechanism within these compounds are discussed, using a novel maximum entropy difference Fourier technique to map the distribution of the Ag+(Cu+) within the unit cell. (C) 2002 Elsevier Science (USA).