High-temperature phase behavior in the Rb₃H(SO₄)₂-RbHSO₄ pseudo-binary system and the new compound Rb₅H₃(SO₄)₄

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• 作者：Chatr Panithipongwut^a ; Sossina M. Haile^a ; ^b ;
• 关键词：Trirubidium hydrogen disulfate ; Rubidium hydrogen sulfate ; Pentarubidium trihydrogen tetrasulfate ; Phase diagram ; A.C. impedance spectroscopy ; X-ray diffraction ; Rb3H(SO4)2 ; RbHSO4 ; Rb5H3(SO4)4 ; Solid acid
• 刊名：Solid State Ionics
• 出版年：2012
• 期刊代码：96_01672738
• 类别：ch
• 出版时间：16 April, 2012
• 卷：213
• 期：Complete
• 页码：53-57
• 文件大小：672 K

摘要

The high temperature behavior of the pseudo-binary system Rb₃H(SO₄)₂-RbHSO₄ has been investigated through a combination of thermal analysis, high-temperature X-ray powder diffraction and high-temperature electrical impedance measurements. The studies reveal the existence of a new high-conductivity phase, Rb₅H₃(SO₄)₄, that becomes stable at a temperature between 25 and 140 掳C and is isostructural to a recently reported trigonal phase of Cs₅H₃(SO₄)₄ [M. Sakashita, et al., Solid State Ionics (2007) 178 1262-1267]. Refinement of the Rb structure in space group P3-m at 160 掳C yields a = 5.9298(2) 脜, c = 14.4736(6) 脜, V = 440.74(3) 脜³, with Z = 1 and 蟻 = 3.0691(2) Mg/m³. At 185 掳C the compound undergoes an apparently polymorphic transformation with a heat of transition of 14.9 kJ/mol and a slight additional increase in conductivity. No further anomalies are observed up to the highest measurement temperature of 220 掳C. Compositions rich in Rb₃H(SO₄)₂ relative to Rb₅H₃(SO₄)₄ show, in addition to the polymorphic transformation of the latter, the disproportionation reaction of the former into Rb₂SO₄ and Rb₅H₃(SO₄)₄ at 205 掳C. Compositions rich in RbHSO₄ display an additional conductivity anomaly at 170 掳C, which is tentatively assigned to a polymorphic transformation in RbHSO₄.