Ambient pressure stabilization of high-pressure superconducting phase of MoB₂ by Nb doping

In the last few years, researchers have discovered many superconductors which are stable only at high pressure. One such high-pressure superconductor is MoB₂ which undergoes a structural transformation from R-3m to P6/mmm MgB₂-like structure at 60GPa and becomes a superconductor below 32K. We show how Nb doping stabilizes the high-pressure MgB₂-like phase, first predicted by theory and then confirmed by experiments. We will present density functional theory calculations that reveal how the MgB₂-like phase is stabilized at ambient pressure by phonon entropy and disorder across the Nb_xMo_1-xB₂ series. The samples used in the experiments were synthesized by arc-melting the elements. X-ray diffraction on our Nb-doped samples confirmed the presence of an MgB₂-like bulk phase in the Nb-doped samples. Our Nb-doped MoB₂ samples are superconducting with the highest Tc of 8K and higher critical fields approaching 6T, as seen in our specific heat and high-field electrical resistivity. The doping method utilized in this work might help stabilize other high-pressure superconducting diborides.