Effect of substituting Fe and Ru for Ni on the thermopower of MgCNi3

The intermetallic perovskite MgCNi3 is a superconductor with a Tc =7 K. Substitution of Fe and Ru for Ni decreases Tc monotonically as the doping concentration is increased. Here we report thermopower measurements S(T) on MgCNi3, MgCNi3-x Fex, and MgCNi3-x Rux. For MgCNi3 the thermopower is negative, -12.5 μV/K, at 300 K. The absolute value of S decreases as x increases in MgCNi3-x Fex and MgCNi3-x Rux. The sign of S changes from negative to positive at low temperatures for values of x>0.01. These data show that the carriers in MgCNi3 are electrons, and by increasing x and decreasing temperature, the participation of hole carriers clearly increases. The influence of the magnetic moments of the Fe atoms on the thermopower is not visible.