Three_phases - One of the rare cases of three phases formed...

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1 One of the rare cases of three phases formed rather than two in a phase separation mechanism Spyridon Koutandos Unpublished work during PhD thesis “Study of the superconductor MgB 2 and the mixed compound Mg x Al 1-x B 2 ” under the supervision of N.T.U.A. and institute Demokritos in Greece PART I . X ray graph analysis of the series Mg 1-x Al x B 2 using 3 phases It is time since the fruitful idea of replacing Mg with Al in the superconductor MgB 2 of especially high T c [1]for its simple structure in certain analogies has been put to action[2,3]. The replacement of Mg with trivalent elements like Al 3+ is expected to donate one more electron in the conduction bands of MgB 2 without altering its structure therefore giving us the chance of studying the changes associated with this procedure. In this paper we focus on the crystallographic structure of the series Mg 1-x Al x B 2 that we constructed and took their X ray graphs from the instrument D500 of the institute of materials science of Demokritos and the “beam line ID31” of ESRF. We have used a new method to prepare a series of samples of the general formula Mg 1-x Al x B 2 with x ranging from 0.05 to 1. The crystallographic system of the alloy Mg 1-x Al x B 2 is P6/mmm with layers of hexagonal structures of Al(Mg) being alternated with layers of honeycomb like lattices of B. In this system Mg and Al occupies the special position (0,0,0) with point symmetry of 6/mmm and B occupies position (1/3,1/3,1/2) with point symmetry -6m2. The c axis measures the distance B-B layers. We studied the X ray graphs of both series by Rietveld refinement of samples adopting a model of 3 phases of the same structure of the P6-mmm system with only different values for the c axis. In the
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This note was uploaded on 12/05/2009 for the course NONE None taught by Professor Spyridonkoutandos during the Spring '09 term at 東京国際大学.

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Three_phases - One of the rare cases of three phases formed...

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