DTA measurements of normal-incommensurate phase transition in (NH4)2ZnCl4 and K2ZnCl4 crystals |
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Authors: | Z Tylczyński P Piskunowicz |
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Affiliation: | (1) Institute of Physics, A. Mickiewicz University, Grunwaldzka 6, 60–780 Pozna, Poland |
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Abstract: | Differential thermal analysis (DTA) was applied to determine the changes in enthalpy and entropy of (NH4)2ZnCl4 and K2ZnCl4 crystals at their phase transition from the orthorhombic normal phase to the incommensurate phase. The temperature of this transition, T
i
, is 406 K for (NH4)2ZnCl4 and 555 K for K2ZnCl4 and the entropy changes (S/R) are 0.053 and 0.035, respectively. The low value obtained for S/R is characteristic of incommensurate phase transitions. The results were compared with the data reported for other crystals of the A2BX4 family. Thermal properties of the crystals of the A2ZnCl4 subgroup were found to the correlated with the length of A-Cl bonds. |
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Keywords: | differential thermal analysis (DTA) phase transition incommensurability |
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