Superconductivity in Transition Metal Doped MoB₄

Polycrystalline ingots of MoB 4 have been found to be superconducting near 6 to 8 K when doped with Ti or Nb. Magnetic susceptibility measurements performed on these alloys indicate that a substantial fraction of the sample volume is superconducting below the transition temperature, while X-ray diffraction scans provide insight into the crystallographic effects of the dopants on the layered MoB 4 structure, revealing both a systematic increase of the lattice constant in the direction of the boron planes and a systematic decrease in the inter-plane spacing as the dopant amount is increased. This structural expansion and contraction corresponds to an increase in T c until the dopant solubility limit is reached. These findings present a stark contrast to the effects of lattice parameter modification on superconductivity in the structurally related AlB 2 -type alloys.