Samples with Mg1−xRuxB2 nominal stoichiometry were prepared by sintering at 800°C. The critical transition temperature decreases up to a substitution level of x≈0.015. A maximum solubility limit slightly in excess of 1at.% Ru for Mg is confirmed by energy dispersive spectroscopy measurements. From and beyond this limit, an unidentified phase appears in the X-ray diffraction patterns. Interestingly, the lattice parameters of the MgB2 phase are constant up to x=0.015, but start to decrease for higher Ru contents. This feature could be related to the fact that a Mg–Ru impurity phase results in a Mg-deficient (Mg,Ru)B2 matrix.
Physica C: Superconductivity and Its Applications, 2013, Vol 495, p. 229-232