Scanning the latent phases and superconductivity in the Nb–Pb system at high pressure

Abstract

So far, few literature studies have been reported on niobium–lead binary intermetallic compounds, which are expected to have very different properties compared to existing niobium–carbon binary compounds, due to the distinct electronic properties of lead when compared to other carbon-group elements. Herein, we carry out a global structure search for the Nb–Pb system based on the evolutionary algorithm and density functional theory. Based on the dynamical and mechanical stability analyses, we unveiled five new phases, P4/m-Nb₉Pb, Cmcm-Nb₃Pb, I4/mmm-Nb₂Pb, Pmm2-Nb₅Pb₃, and I4/mmm-NbPb₂, that are promising candidates for experimental synthesis. Moreover, the superconducting transitions of all Nb–Pb binary intermetallic compounds are performed with electron–phonon calculations. As Nb₉Pb exhibited the maximum T_c in the Nb–Pb intermetallics, greater than 3.0 K at 20 GPa, the phonon band structures, partial phonon density of states (PHDOS), the corresponding Eliashberg spectral functions α²F(ω), and integral electron–phonon coupling (EPC) parameters λ as a function of frequency of Nb₉Pb were also studied. This work filled the gap in the pressure-tuned Nb–Pb phase transitions from a systematic first principles study for the first time.