Superconductivity of embedded lead nano particles in metallic and amorphous matrices
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Superconductivity of embedded lead nano particles in metallic and amorphous matrices K. Chattopadhyaya, V. Bhattacharyaa and A. P. Tsaib a Indian Institute of Science, Bangalore-560 012, India b National Research Institute for Metals, Tsukuba 305-0047, Japan ABSTRACT Nanodispersed lead in metallic and amorphous matrices was synthesized by rapid solidification processing. The optimum microstructure was tailored to avoid percolation of the particles. With these embedded particles it is possible to study quantitatively the effect of size on the superconducting transition temperature by carrying out quantitative microstructural characterization and magnetic measurements. Our results suggest the role of the matrices in enhancement or depression of superconducting transition temperature of lead. The origin of this difference in behavior with respect to different matrices and sizes is discussed. INTRODUCTION The early observations on the importance of normal-superconductor junctions were made in 1930 [1]. Since then a large body of literature are available on the subject. Intensive theoretical and experimental investigations were carried out in the sixties and seventies on granular superconductors and thin films [2,3,4]. Recently, there is a resurgence of interest due to the increasing interest in nanoscience and technology which demands understanding the behaviour of small particles [5-9]. Rapid solidification technique has been extensively used to synthesize nanoembedded particles of immiscible alloy [10]. We have successfully synthesized nanosized Pb dispersed in different matrices using this technique. In the present paper, we report the superconductive behaviour of these nanosized Pb particles embedded in Al and Al-based metallic glass matrices. EXPERIMENTAL PROCEDURE Nanoembedded lead in aluminium and amophous glassy matrix was synthesized via melt spinning using 99.999%Al, Cu, V and 99.99%Pb. An optimum composition and quenching rate was chosen in order to obtain a well-dispersed microstructure. Lead is insoluble in aluminium, and in all the three elements constituting the Al75Cu15V10 matrix both in the liquid state and the solid state. The processing resulted in an aluminium matrix with nanodispersions of lead, and a metallic glass matrix with nano lead dispersions. . Preliminary phase identification of the samples were carried out by X-ray diffraction (JEOL model JDX 8030 ) using Cu Kα radiation. Microstructural characterisation was done using a JEOL 2000 FX-II Transmission Electron Microscope (TEM) and HREM. The size distributions of particles were carried out using a V13.22.1
Sigma scan Pro commercial software. Magnetic measurements were carried out in a SQUID magnetometer in standard configuration. The magnetization tests were conducted under identical conditions in zero field-cooled state in order to avoid the interference of macroscopic persistent screening currents flowing in the sample. Typical fields of 20Oe & 100Oe were chosen for measurements. RESULTS The composition of Pb in Al was 6.5wt% and in Al75C
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