Mg1−xCrxB2 polycrystal bulk samples with x = 0 to 5% were synthesized by a solid-state reaction and studied by X-ray diffraction, scanning electron microscopy and Raman spectrum. It was found that the c-axis of the lattice decreased as the Cr content increased, while the a-axis remained unchanged. Moreover, crystal grain size increased apparently with Cr doping concentration increase. The normal-state resistivity increased and the superconducting transition temperature decreased from 38.2K (x = 0) to 35.1K (x = 0.03) with increasing Cr content. It was suggested that the charge transfer between the Mg-layer and the B-layer causes the decrease of the charge carrier concentration and induces the changes of TC and normal-state resistivity. On the other hand, by the Raman scattering study, it was found that the line-width of Raman spectrum increased with the increase of Cr content, which was resulted by the competition between the electron–phonon interaction and substitution-induced disorder. The Raman peak had no evident shift due to the countervailing between the effects of the electron–phonon coupling and the grain size.

The Charge Transfer Induced by Cr Doping in MgB2. H.Zhang, J.Zhao, L.Shi: Physica C, 2005, 424[1-2], 79-84