Heat Capacities and Phase Transitions of the Molecule-Based Mixed-Valence Complex NBu_4[Fe^<II>Fe^<III>(ox)_3] and the Mixed-Metal Complex NBu_4[Zn^<II>Fe^<III>(ox)_3] : Condensed Matter: Structure, etc.
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概要
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Heat capacities of two molecule-based materials NBu_4[Fe^<II>Fe^<III>(ox)_3] and NBu_4[Zn^<II>Fe^<III>(ox)_3] (Bu=nbutyl, ox=oxalate) were measured by adiabatic calorimetery. In case of ferrimagnetic NBu_4[Fe^<II>Fe^<III>(ox)_3] tow phase transitions were detected at 43.3 K (T_2) and 217 K (T_1) along with a small heat capacity anomaly at 16.3 K (T_3). The heat capacity anomaly at 43.3 K is due to the ferrimagnetic ordering, whereas that at 217 K has been assigned to an order-disorder phase transition due to increasing conformational change of the organic cation. The small heat capacity anomaly at T_3 seems to arise from a spin glass like state at low temperatures. The enthalpy and entropy gains from the heat capacity anomalies at T_1, T_2 and T_3 are 2.29kJmol^<-1> and 11.47JK^<-1>mol^<-1>; 1.37kJmol^<-1> and 22.65JK^<-1>mol^<-1>; 0.068kJmol^<-1> and 4.89JK^<-1>mol^<-1>, respectively. The sum of the entropies (=27.54JK^<-1>mol^<-1>) corresponding to the heat capacity anomalies at T_2 and T_3 is very close to the expected magnetic entropy R In 30 (=28.27JK^<-1>mol^<-1>) for the spin multiplicity of high spin Fe^<III> and Fe^<II> ions. No phase transition around 38 K has been detected, as predicted from previous magnetic measurements. In case of paramagnetic NBu_4[Zn^<II>Fe^<III>(ox)_3] a heat capacity anomaly due to a similar order-disorder phase transition was observed at 227 K accompanied with the enthalpy and entropy gains of 2.91kJmol^<-1> and 13.32JK^<-1>mol^<-1>, respectively. A model has been applied to realize the high temperature order-disorder phase transition.
- 社団法人日本物理学会の論文
- 2000-02-15
著者
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MIYAZAKI Yuji
Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka University
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Miyazaki Y
Research Center For Molecular Thermodynamics Graduate School Of Science Osaka University
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Sorai Michio
Research Center For Molecular Thermodynamics Graduate School Of Science Osaka University
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BHATTACHARJEE Ashis
Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka University
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Bhattacharjee A
Osaka Univ. Osaka
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Bhattacharjee Ashis
Research Center For Molecular Thermodynamics Graduate School Of Science Osaka University
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Sorai Michio
Research Center for Molecular Thermodynamics,Graduate School of Science,Osaka University
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