Influence of Mg deficiency on the properties of MgB2

The samples of Mg deficiency with different Mg nominal content (Mg1-xB2) are prepared by the solid-state reaction method at the sintering temperatures of 900 and 640 degreesC. The effects of Mg deficiency on the structure and superconducting properties are investigated by the Rietveld refinement of X-ray powder diffraction and the resistance measurement, respectively. The results show that the lattice parameters of the samples sintered at different temperatures are of a similar variation, i.e., a decreasing and c increasing with increasing x, respectively. T-c of the samples decreases with increasing x and the maximum T-c variation of DeltaT(c)(T-c(max) - T-c(min)) similar to 2 K is observed for samples sintered at high temperature. It is concluded that the nominal Mg content reduction does not give rise to serious Mg deficiency and slight Mg deficiency does not result in a remarkable change of T-c and normal state properties of the samples. (C) 2002 Published by Elsevier Science B.V.