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The application of conduction calorimetry for specific heat measurements on samples under non-equilibrium conditions is reviewed.

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Abstract  

The lattice specific heat in carbon nanotubes is evaluated within the microscopic model proposed by Mahan and Jeon, published in the Physical Review B, in 2004. Phonons are considered for single wall carbon nanotubes in armchair configuration. As expected, low temperature and high temperature regions show different behaviour of specific heat. Carbon nanotubes are also displaying a very interesting lattice transport depending on the tube diameter, with high thermal conductivities for small diameters.

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Journal of Thermal Analysis and Calorimetry
Authors: I. Ruiz-Larrea, A. Fraile-Rodríguez, A. Arnáiz, and A. López-Echarri

Abstract  

New measurements of the (N(CH3 )4 )2 MnBr4 specific heat by adiabatic calorimetry around the ferro- paraelastic phase transition shown by the crystal around 276 K are compared with previous calorimetric studies on similar tetramethylammonium bromide compounds. The thermodynamic behaviour of the tribromides and tetrabromides derivatives together with the influence on the phase transition parameters of the cation and halogen molecular substitutions are examined. The thermal relaxation experiments permit to study the behaviour of the crystals thermal conduction as a function of the temperature. Finally, the Landau theory for second order phase transitions is used to describe the thermodynamic behaviour of some of these crystals.

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Summary Specific heat data and their relation to the form of the energy gap are reviewed for Al, HfV2, and two recently discovered superconductors, MgB2 and Na0.3CoO2·1.3H2O. The data for Al and HfV2 exemplify the specific heat of, respectively, weak- and strong-coupled BCS superconductors with isotropic energy gaps. MgB2 is also known to be a BCS superconductor, but the specific heat deviates from BCS behavior in a way that shows the presence of two distinctly different energy gaps and characteristics of both weak and strong coupling. The heat capacity of Na0.3CoO2·1.3H2O is strongly sample dependent, but suggests that it is another two-gap, possibly ‘unconventional’ superconductor.

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A new differential scanning calorimeter NETZSCH model DSC 404 C Pegasus was developed for the measurement of specific heat and transformation energetics. The system allows tests between -120 and 1650C with high accuracy. Presented in this work are the design of the DSC and measurements on various kinds of materials such as ceramics and metals, demonstrating the capability of the new system at low temperatures as well as in the high-temperature region.

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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 antiferromagnetic phase transitions in a CuO single crystal are studied by specific heat in magnetic fields up to 6T. The magnetic field dependence of the incommensurate-to-commensurate-antiferromagnetic transition atT L is found to be highly anisotropic.T L is observed to increase nonlinearly for Bac-axis, whereas, a linear reduction is observed forB ab-axis. The magnetic field dependence ofT L and the jumps in magnetic susceptibility atT L are explained thermodynamically using the Clausius-Clapeyron equation.

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We describe a fully automated adiabatic calorimeter designed for high-precision covering the temperature range 15 to 300 K. Initial measurements were performed on synthetic sapphire (20 g). The statistical error of the apparatus estimated from the scattering of theC p data of sapphire is about 0.1% and the average absolute error of specific heat between 100 and 300 K was 0.7% compared to values given in the literature. The heat capacity and the three phase transitions of cyclopentane (C5H10) which is recommended as a standard for the temperature calibration of scanning calorimeters have also been measured. The transition temperatures were determined to be (literature values in parentheses): 122.23 K (122.39 K) 138.35 K (138.07 K) and 178.59 K (179.69 K), with an experimental error of ±40 mK.

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Abstract  

Fe–B ultrafine amorphous alloy particles (UFAAP) were prepared by chemical reduction of Fe3+ with NaBHO4 and confirmed to be ultrafine amorphous particles by transmission electron microscopy and X-ray diffraction. The specific heat of the sample was measured by a high precision adiabatic calorimeter, and a differential scanning calorimeter was used for thermal stability analysis. A topological structure of Fe-B atoms is proposed to explain two crystallization peaks and a melting peak observed at T=600, 868 and 1645 K, respectively.

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Journal of Thermal Analysis and Calorimetry
Authors: Y. Akishige, H. Shigematsu, T. Tojo, H. Kawaji, and T. Atake

Summary Specific heats on the single crystals of Sr2Nb2O7, Sr2Ta2O7 and (Sr1-xBax)2Nb2O7 were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T INC (=495 K) on Sr2Nb2O7 and at the super-lattice phase transition of T SL (=443 K) on Sr2Ta2O7; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T LOW (=95 K) on Sr2Nb2O7. The transition temperature T LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.

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