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Abstract  

The paper gives a review on recent progress on new methods, instrumental innovations and new trends in low temperature calorimetry as reported in the last five years in the literature. The paper refers to establishing strictly adiabatic conditions, improved analysis of quasi-adiabatic experiments, high resolution adiabatic and isoperibol scanning calorimeters and microcalorimeters for the study of µ-samples.

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The construction and operation of a new fully automated microcalorimeter is described.This instrument allows specific heat measurements to be performed on small samples in the 10 mg-range at low temperatures (10 K <T < 350 K). The new method consists of ombining the non-adiabatic relaxation-time calorimetry with a twin arrangement and simultaneous temperature scanning. Some experimental details of the calorimeter and sample holders are presented. The accuracy of the calorimeter was verified by calibration measurements on 56 mg of copper. An energy resolution of 0.1μJ/K has been reached near 12 K. To demonstrate the reliability of the microcalorimeter the heat capacity of the new highT c superconductor YBa2Cu3O7−y, was determined.

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Abstract  

The pyrochlores RE2Mo2O7 (RE=Y, Sm, Gd, Ho) display, with the exception of Ho2Mo2O7, magnetic transitions at 18 K, 68 K, 55 K, respectively. No long-range order occurs. The rare-earth atoms remain in the paramagnetic state down to 1.5 K. The magnetic specific heat behaviour is explained by spin-glass-like ordering of Mo4+ ions, imposing a molecular field of random character on the rare-earth ions, and by crystalline field-splitting effects.

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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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Abstract  

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  

The heat capacities of eight chlorine boracites T3B7O13Cl (T=Cr, Mn, Fe, Co, Ni, Cu, Zn or Mg) have been measured in the temperature range 2 to 100 K. Magnetic phase transitions occur below 20 K in the compounds studied except in the two non-magnetic substances Zn3B7O13Cl and Mg3B7O13Cl. The magnetic specific heat capacities give information on magnetic ground state of the transition metals and the entropy related to the phase transitions.

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Chemistry and structural chemistry of phosphides and polyphosphides 51

Thermodynamic properties of [Ag6M4P12]Ge6 (M=Ge, Sn)

Journal of Thermal Analysis and Calorimetry
Authors: E. Gmelin, W. Hönle, Ch. Mensing, H. G. von Schnering, and K. Tentschev

The heat capacities of thecluster compounds [Ag6M4P12]Ge6 (M=Ge, Sn) have been measured in the temperature range from 2 K to 310 K. Thermal decomposition into the elements was carried out under Knudsen conditions on a thermobalance combined with a mass spectrometer. The thermodynamic functions standard entropy, enthalpy, and the Debye temperatures were calculated from the heat capacity data. The vapour pressure functions derived from the Knudsen effusion data, served to calculate the third law heat of formation.

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