23 August 1995 Thermodynamic studies of thermochromic phase transition in coordination compound of iron with triazole
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The aim of this work was to investigate the thermodynamic properties of nitrate tris(4-amino- 1,2,4-triazole) iron(II) for which a thermochromic effect takes place at T equals 342 K on heating and at 310 K on cooling. For the measurement of the isobaric heat capacity in the 5 - 355 K range, a vacuum adiabatic calorimeter was used. Below 300 K, the Cp,m(T) curve has no anomalies; the average deviation of the experimental heat-capacity values from the smoothed Cp,m(T) curve was 0.1 percent. Above 300 K, the Cp,m(T) curve shows a complicated behavior. The abnormal part of the heat capacity first increases smoothly, then from 330 K a sharp rise begins. There is a peak on the Cp,m-curve at T equals 343.0 K. This fact is in a good agreement with the magnetic measurement data. The transition enthalpy was determined to be 22.8 kJ(DOT)mol-1 (M equals 432.10 g(DOT)mol-1). Further increase of the heat capacity suggests the existence of a new phase transition above 350 K. This suggestion was confirmed qualitatively by the measurements on a differential scanning calorimeter. It should be noted that on the low- temperature slope of the anomaly, at 320 < T < 330 K, there is a small anomaly with the maximum deviation of 5 - 10% from the regular part. To compare the phonon characteristics, the heat capacity of nitrate tris(4-amino-1,2,4-triazole) copper(II) was studied.
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V. G. Bessergenev, V. G. Bessergenev, G. A. Berezovski, G. A. Berezovski, L. G. Lavrenova, L. G. Lavrenova, Stanislav Vasiljevic Larionov, Stanislav Vasiljevic Larionov, "Thermodynamic studies of thermochromic phase transition in coordination compound of iron with triazole", Proc. SPIE 2531, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIV, (23 August 1995); doi: 10.1117/12.217343; https://doi.org/10.1117/12.217343

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