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Effects on transition temperature and Raman spectra of substitution of Cr and Al for Mg in MgB 2
Author(s) -
Shi Lei,
Zhang Huarong,
Zhou Shiming,
Jia Yunbo,
Chen Lin
Publication year - 2007
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200642317
Subject(s) - raman spectroscopy , crystallite , laser linewidth , crystallography , chemistry , diffraction , doping , lattice (music) , crystal structure , condensed matter physics , physics , laser , acoustics , optics
Mg 1− x M x B 2 (M = Cr, Al) polycrystalline bulk samples with 0 ≤ x ≤ 5% have been synthesized by a solid state reaction and studied by X‐ray diffraction, SEM and Raman spectroscopy. By comparing with the results of Sc‐substituted MgB 2 , it is found that all these atomic substitutions for Mg depress T c , and Cr and Sc substitutions depress T c even more quickly than the one of Al doping. It is suggested that the T c changes of the M‐substituted MgB 2 can be understood by the competing/cooperating effects of the hole‐filling and the disorder. The Raman peak linewidth decreases for Al‐substituted MgB 2 , which represents an opposite trend to the linewidth change of Mg 1− x Cr x B 2 and shows an evidence of the disorder caused by the atomic substitution and the different arrangement of the substituted atoms in the lattice. Meanwhile, different frequency changes of the Raman peak for the Cr‐ and Al‐substitute MgB 2 are discovered and understood by the competing/cooperating effects of the electron‐phonon coupling, the grain size, and the lattice contraction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)