Search Results - (Author, Cooperation:J. L. Jorda)

2011-08-27

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

0921-4526

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4526

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

0921-4526

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

1572-8943

DTA ; high temperature superconductors ; phase diagrams ; TG ; thermal analysis

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Abstract With the discovery of high temperature superconductivity an extraordinary field for investigations on new materials containing up to (more than) 8 or 9 components has been open. But, in addition to problems specifically related to superconductivity, we are faced with a prelimary difficulty: the preparation of well defined compounds which may have reproducible properties. This difficulty is smoothed out when the phase relations in the relevant systems are known. Differential Thermal Analysis (DTA) contributes to their establishment. However, in multicomponent systems, an isopletic line is expected to intercept various boundary surfaces and the analysis is obviously complicated, compared to low order systems. In addition, by the nature of high temperature superconductors the oxygen partial pressure used for their preparation is an important thermodynamic parameter which contributes to fix the oxygen content in the solid state. During heat treatments, the composition of the systems may change, due to oxygen or volatile oxides (Tl2O3, PbO2 or HgO) release. A permanent composition control then requires thermogravimetric (TG) measurements associated to DTA. This paper attempts to demonstrate the efficiency of the assembly DTA/TG for the study of high temperature superconductors. Going beyond the frame of preparation and quality control, the system is also particularly useful for kinetic studies. Examples will be principally in the (Tl,Pb)-(Ba,Sr)-Ca-Cu-O systems.

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Bulk samples covering the entire homogeneity range of the Nb-Sn A15-phase were prepared by a new method: levitation melting under high argon pressure. The variations of the lattice parameter, superconducting transition temperature, resistivity and critical field slope were measured as a function of composition. A low-temperature X-ray diffraction study was undertaken in order to fix the compositional limit of the tetragonal phase. The theoretical expectations for the critical field slopes at the transition temperature, T c, based on actually-observed alloy parameters, were found to be in good agreeement with measured values.

Electronic Resource

1573-7357

Springer Online Journal Archives 1860-2000

Physics

Abstract The specific heat of Nb0.75Zr0.25 is measured from 1.2 to 50 K in zero magnetic field. A phonon density of statesF(ω) and a spectral electron-phonon coupling function α2(ω)F(ω) are fitted to the data in the normal state and in the superconducting state. The results are compared with a previous similar analysis of the specific heat of pure Nb and with published tunneling data. It is found that in Nb0.75Zr0.25, λ−μ*=1.13, ωlog=109 K, and N(0)=0.85 eV−1 at−1 spin−1, compared with the figures 0.84, 146 K, and 0.85 eV−1 at−1 spin−1, respectively, in pure Nb. These data confirm that the increase ofT c upon the alloying of Nb with Zr is due to phonon softening. They further show that the electronic density of states at the Fermi level is identical in Nb and Nb0.75Zr0.25. Dimensionless thermodynamic ratios predicted from tunneling data are entirely confirmed, thus confirming the internal consistency of the Eliashberg theory for superconductivity.

Electronic Resource

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract The ferroelastic domains of the orthorhombic phase of YBa2Cu3O7-σ have been observed in polarized light on ceramics and single crystals. By combining polarized light microscopy with the X-ray precession technique, the correlation of the orientation of the orthorhombica- andb-axes with that of thea-b-plane bireflectance, reflection dichroism, transmission dichroism (at a thickness of about 1μm), reflection tints generated with compensators and upon uncrossing of polars, as well as the orientation of etch pits has been realized on ferroelastic single domains, bi-domains and more complicated domain patterns. Four ferroelastic orthorhombic domain states have been identified, at variance with former group theoretical considerations, predicting only two states. Ensembles of lamellar domains beyond optical resolution generate strong bireflectance with principal axes rotated by 45° relative to the truea, b-directions.

Electronic Resource

1572-8943

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Zusammenfassung Der Hochtemperaturteil (T〉1600 K) des Phasendiagramms des binären Systems Zr-Rh und die Ergebnisse diesbezüglicher kalorimetrischer Messungen werden mitgeteilt. Fünf intermetallische Verbindungen (Zr2Rh, ZrRh, Zr3Rh4, Zr3Rh5 und ZrRh3) treten im Phasendiagramm auf. Die Bildungsenthalpie von Zr2Rh, ZrRh und ZrRh3 wurde bestimmt und durch Optimierung des Phasendiagramms verfeinert. Eine thermodynamische Beschreibung des Systems wird gegeben.

Резюме Представлены высоко температурная (Т〉 1600 К) часть фазовой диагра ммы и калориметрические и сследования двойной системы Zr-Rh. На сложной фазовой ди аграмме идентифицированы пя ть интерметаллическ их соединений Zr2Rh, ZrRh, Zr3Rh4, Zr3 Rh5 и ZrRh3. Измеренные энтальпи и образования фаз Zr2Rh, ZrRh и ZrRh3 были угочнены на основе оптимизации фазовой диаграммы. Предложен о термодинамическое о писание данной систе мы.

Abstract High temperature (T〉1600 K) part of the phase diagram and calorimetric studies in the binary Zr-Rh system are presented. Five intermetallic compounds: Zr2Rh, ZrRh, Zr3Rh4, Zr3Rh5 and ZrRh3 are present in the compositional phase diagram. The enthalpy of formation of Zr2Rh, ZrRh and ZrRh3 have been measured and refined from an optimization of the phase diagram. A thermodynamic description of the system is proposed.

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract We present a new method of thermal analysis based on the position change during melting of samples heated in an electromagnetic levitation coil. The temperature is measured with a two-colour pyrometer, subject to appropriate corrections. This method appears to be a useful complement to other investigations such as differential thermal analysis (DTA) or “simultaneous stepwise heating”. The technique has been applied to the determination of the melting temperatures of alloys in the Nb-rich part of the Nb-Ge system.

Electronic Resource