Superconductivity in Transition Metal Doped MoB4

Abstract

Polycrystalline ingots of MoB4 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 sam- ple volume is superconducting below the transition temper- ature, while X-ray diffraction scans provide insight into the crystallographic effects of the dopants on the layered MoB4 structure, revealing both a systematic increase of the lattice constant in the direction of the boron planes and a system- atic decrease in the inter-plane spacing as the dopant amount is increased. This structural expansion and contraction cor- responds to an increase in Tc until the dopant solubility limit is reached. These findings present a stark contrast to the ef- fects of lattice parameter modification on superconductivity in the structurally related AlB2-type alloys.