Effect of carbon doping on the structure and superconductivity in AlB2-type (Mo0.96Ti0.04)0.8${(\text{Mo}_{0.96}\text{Ti}_{0.04})}_{0.8}$B-2

We report the effect of carbon doping in Ti-stabilized nonstoichiometric molybdenum diboride (Mo0.96Ti0.04)0.8${(\text{Mo}_{0.96}\text{Ti}_{0.04})}_{0.8}$B-2, which exhibits bulk superconductivity below T-c = 7.0 K. It is found that (Mo0.96Ti0.04)0.8${(\text{Mo}_{0.96}\text{Ti}_{0.04})}_{0.8}$(B1-xCx)2${(\text{B}_{1-x}\text{C}_{x})}_{2}$ maintains the AlB2-type phase with a uniform elemental distribution for x = 0.12 and 0.16. The substitution of carbon for boron leads to a slight increase in a-axis, a remarkable reduction in c-axis, the formation of planar defects along the (100) crystallographic planes, and a shift of the B 1s peaks toward higher binding energies. Contrary to (Mo0.96Ti0.04)0.8${(\text{Mo}_{0.96}\text{Ti}_{0.04})}_{0.8}$B-2, however, no superconductivity is observed down to 1.8 K for the C-doped samples, which is ascribed to the electron filling of boron pi bands resulting from the carbon doping.