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Abstract  

Heat capacity measurements were carried out on single-crystalline CuO in the temperature range 130–300 K. Sharp peaks corresponding to the antiferromagnetic transitions were clearly observed at 211 and 227 K. At the low-temperature end, near 160 K, a wide peak in the heat capacity signal was also demonstrated. An electric anomaly was observed in the temperature range 150–160 K, which strongly suggests the possibility of a new low-temperature phase transition in CuO. This study also indicates that DSC measurement is an effective tool to detect magnetic transitions and probe subtle phase transitions in solids.

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Abstract  

The paper studies metastable phases of 4,4'-di-n-heptyloxyazoxybenzene (liquid crystal substance) using adiabatic calorimetry. The process of transformation between metastable and stable phases is described quantitatively. The conclusion concerns activation energies for metastable phase to stable phase transition.

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Abstract  

Positron lifetime spectroscopic and Dopplerbroadening measurements have been carried out on trans-stilbene single crystals. The results (including the complementary DSC measurement) give new evidence for the existence of phase transitions in trans-stilbene at temperatures between 20 and 300 K.

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Abstract

The specific heat and the enthalpy variation of a highly deuterated crystal of ferroelectric triglycine selenate have been measured around its first-order phase transition using the technique square modulated differential thermal analysis (SMDTA). The low temperature variation rate has allowed analyzing the kinetics of the phase transition. Due to an internal crack in the sample, the transition is carried out in two steps and an intermediate region where the transition is blocked and both phases coexist without transformation has been found. The latent heat on cooling (L c=1.32±0.02 J g−1) is higher than on heating (L h=1.08±0.02 J g−1) due to the thermal hysteresis and the great difference between the specific heat in both phases. Nevertheless, the enthalpy balance is fulfilled on heating and on cooling.

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Abstract  

The study of trans- and cis-1,2-cyclohexanediol by infrared spectroscopy was performed. The variation of the maximum frequency and of the bandwidth of the OH stretching vibration give evidence of the role played by hydrogen bonding in the solid and liquid phases of both isomers and allows to follow the phase transitions. A solid rotator phase is shown for the cis compound.

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Abstract  

In this study we used differential scanning calorimetry to clarify the role of water activity within the nano-droplets, and to explore phase transitions in novel phospholipids based fully dilutable food-grade microemulsions. The microstructure transitions were investigated along two water dilution lines (50:50 and 80:20 mass% surfactant mixture/oil phase). From the water thermal behavior we learned that three structural regions can be identified along the water dilution lines. The thermal transition points coincide with the structural phase transition of the microemulsions as measured by other methods (electrical conductivity and SD-NMR measurements). The structural transitions were detected at 20 and 45 mass% of water along dilution line 55, where along dilution line 82 it occurs at 40 and 50 mass% of water. The microemulsions along dilution line 82 seem to have more compact surfactant packing film, thus the film has stronger resistance to transformation upon dilution, resulting in a smaller bicontinuous region than the one formed at dilution line 55. The difference in phase transition point can be used for triggering the release of future solubilizate.

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Abstract  

The phase transition from the solid state to the liquid crystal state was investigated for the copper(II) salts of the fatty acids with 10, 12, 14, 16 or 18 carbon atoms in the chain, by measuring the temperature dependence of the conductance and capacitance of a cell containing the material under investigation. The temperatures deduced from these dependences agree reasonably with those found by DSC measurements and with those to be found in the literature. Differences in dielectric behaviour between the samples are qualitatively discussed.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Igartua, G. Aguirre-Zamalloa, I. Ruiz-Larrea, M. Couzi, A. López-Echarri, and T. Breczewski

Abstract  

The specific heat of N(CH3)4CdBr3 from 50 to 300 K has been measured by adiabatic calorimetry, using both static and dynamic methods. The obtained results have permitted a careful study of the ferro-paraelectric phase transition the crystal shows at 160 K. The available spectroscopic data have been used to generate a reliable baseline which accounts for the normal lattice contribution to the specific heat. These results allow for an accurate estimation of the phase transition thermodynamic functions: ΔH=2620 J·mol−1 and ΔS=18.04 J·(mol°C)−1. These high values are in agreement with the predictions of the 6 well potential Frenkel model.

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The thermal conductivity of LiKSO4 ferroelastic crystals was measured along the three principal crystallographic axes in the vicinity of its high temperature phase transition at 750 K. The data showed an anomalous behaviour in the temperature dependence of the thermal conductivity in the transition region of width of about 25 degrees. The anomaly in the phonon contribution to the conductivity was referred to the freezing-in of either optic-and/or acoustic-modes of lattice vibrations in the near vicinity of the phase transition. The results are discussed in terms of scattering mechanisms of energy carriers.

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The phase transition in KHSO4 crystals of varying deutrium content and different Cu2+ concentration is studied. The specific heat at constant pressure,C p, and DTA measurements are investigated. The measurements are carried out in the vicinity of phase transitionT c=468 K. Multiple peaks are observed in the temperature dependence ofC p and a noticeable change due to Cu2+ dopant. This behaviour can be attributed to the fact of order disappearance in partial melting of proton in sublattice.

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