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Abstract  

The thread that runs through all research in the field of superconductivity is new physics through discovery of new materials. The knowledge of superconducting materials has become voluminous and complex. The comprehensive review of the superconducting materials is of particular importance. The main purpose of this report is to present the results of classification for chalcogenide superconductors. Superconducting critical temperature T c, crystal-structure type and the references proper to these compounds are summarized. Brief survey of the superconductivity in chalcogen elements is also given. Furthermore, as representative sulfide and selenide, superconducting characteristics of CuRh2S4 and CuRh2Se4 will be shown.

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Abstract  

The heat capacity of 9.70 and 11.35 mol% yttria stabilized zirconia ((ZrO2)1–x(Y2O3)x; x=0.0970, 0.1135) was measured by adiabatic calorimetry between 13 and 300 K, and some thermodynamic functions were calculated and given in a table. A large excess heat capacity extending from the lowest temperature to room temperature with a broad maximum at about 75 K was found in comparison with the heat capacity calculated from those of pure zirconia and yttria on the basis of simple additivity rule. The shape of the excess heat capacity is very similar to the Schottky anomaly, which may be attributed to a softening of lattice vibration. The amount of the excess heat capacity decreased with increasing yttria doping, while the maximum temperature did not vary. The relationships among the excess heat capacity, defect structure and interatomic force constants, and also the role of oxygen vacancy were discussed.

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Abstract  

Y2O3 has a crystal structure of c-type rare-earth oxide. Y2O3 does not show an oxide ionic conductivity. On the other hand, CeO2 based oxide is one of the most interesting of the fluorite oxides since the ionic conductivity of it is higher than that of yttria-stabilized zirconia. However, CeO2 based oxides are partially reduced and develop electronic conductivity under reduced atmosphere.In this study, the effective index for the improvement of ionic conductivity in Y2O3 and CeO2 systems was defined using ionic radii from the viewpoint of crystallography. The utility of this effective index on some electrical properties was investigated.

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Abstract  

The phase transition and the crystal structures of CuITe were investigated by differential thermal analysis and X-ray powder diffraction measurements in the temperature range between 300 and 683 K. The new phase transition in CuITe was observed at 592 K. The enthalpy of transition is ΔH=0.125 kJ mol-1. The new phase above 592 K belongs to tetragonal system with the space group I41 /amd.

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Abstract  

In this study, GdBaSr(Cu3−x M x)O7−δ bulk samples (M=Zn and Ni; 0≤x≤0.1) were prepared via solid-state reaction. Specific heat measurement (measured with thermal relaxation technique using PPMS) shows an obvious specific heat jump around the T c for GdBaSrCu3O7−δ sample as observed in most of the high temperature superconductors. It shifts towards lower temperature with increasing of both Zn and Ni doping contents, whose tendency is similar to the decreasing of T c. Debye temperature, ΘD (derived from specific heat measurements) calculated at around 10 K is found to be directly proportional to the T c.

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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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Abstract  

The phase transitions of α,α-trehalose dihydrate (T h) were investigated by either differential thermal analysis (DTA) with an in-house apparatus of variable-pressure type equipped with an open sample holder or commercially available TG (thermal gravimetry)-DTA apparatus for comparison under the same experimental conditions as to the heating rate (2°C min−1), the type of pan (open), and the particle size of T h (63 μm). The former DTA measurements were carried out under five different total pressures, 101, 75, 61, 48 and 35 kPa, which provided quite helpful information necessary for confirmative assignments of the endothermic peaks due to either melting or dehydration of T h. The usage of largely different amount of T h, 126 and 14 mg for the DTA and TG-DTA measurements respectively, led to their different DTA traces, showing that there were largely different extents of the influence by the measured sample surface exposed to the surrounding atmosphere on its dehydration behavior. In addition the high thermal sensitivity achieved with such mass of T h gave rise to an interesting discovery of an unidentified thermal event at 92°C prior to either melting or dehydration of T h.

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Abstract  

The structural characterization, thermogravimetric analysis and electrical properties for solid solution system, (Ba1–xLax)2In2O5+x with perovskite-type structure were investigated. X-ray diffraction showed that the orthorhombic phase was in the range of 0.0<x 0.3, the tetragonal phase 0.3<x 0.5, and the cubic phase 0.5<x. The sharp transition of electrical conductivity shifted to a lower temperature with increasing x and disappeared at the phase boundary between the orthorhombic and tetragonal phases. This perovskite-related oxide exhibited a pure oxide-ion conduction over the oxygen partial pressure range of 1 atm to 10–3.5 atm, and the electrical conductivity reached the value of 1.610–1 (S cm–1) at 1073 K, which was nearly equal to that of the yttria stabilized zirconia. These properties were successfully explained in terms of disordered oxygen ions.

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Summary The size effect on the crystal structure including the chemical bonding nature has been investigated for several kinds of BaTiO3 nanopowder with the particle sizes down to 50 nm in diameter, by means of powder diffraction using high-energy synchrotron radiation. The Rietveld refinement reveals that the BaTiO3 nanopowder consists of tetragonal and cubic structure components at 300 K. The feature of coexistence can be illustrated by the core/shell model for the particle, in which the shell with a cubic structure covers the core with a tetragonal structure. The thickness of the cubic shell is almost constant irrespective of the particle sizes, and is estimated as approximately 8 nm. Hence, the critical particle-size, where the entire particle is covered with the cubic shell, is suggested as 16 nm. The charge density distributions of the BaTiO3 nanopowder in the cubic phase at 410 K are revealed by the maximum entropy method. Changes in the bonding electron density and the ionic valence expected are not observed clearly even in the 50 nm crystal compared with the bulk crystal.

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