Orientational and positional disorder of ions and its freezing in the CsNO2-TlNO2 system2 |
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Authors: | Keiichi Moriya Takasuke Matsuo Hiroshi Suga |
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Institution: | Department of Chemistry and Chemical Thermodynamics Laboratory, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan |
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Abstract: | The heat capacities of Cs0.695Tl0.305NO2 (Specimen I) and Cs0.385Tl0.615NO2 (Specimen II) have been measured between 14 and 350 K. Specimen I underwent a phase transition at (197.7 ± 0.1) K, with ΔS = (19.2 ± 1.5) JK?mol?, and specimen II at (214.5 ± 0.2) K, with ΔS = (5.4 ± 1.0) JK?1mol?1, respectively. Above the phase transition, an exothermic temperature drift due to phase separation was observed. Annealing of the sample at 203 K for 300 hr brought about complete phase separation. The solid solution system annealed at 203 K gave two heat capacity peaks at (203.3 ± 0.1) K, with ΔS = (13.8 ± 0.8) JK?1 mol?1, and (242.4 ± 0.2) K, with ΔS = (10.6 ± 1.3) JK?1 for Specimen I, and at (203.0 ± 0.1) K with ΔS = (6.7 ± 0.5) JK?1 mol?1, and (257.5 ± 0.2) K with ΔS = (17.9 ± 1.7) JK?1 mol?1 for Specimen II. The phase diagram of the CsNO2-TlNO2 binary system was constructed on the basis of DTA, heat capacity and dielectric measurements. In the metastable phase, the existence of a residual entropy due to the freezing of a random distribution of Cs+1 and Tl+ cations in addition to the orientational disorder of the NO2?1 ion was confirmed by a comparison of entropies of the stable and the metastable phases. |
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