Although niobium borides have been extensively studied
on their
mechanical properties, a systematic investigation on their potential
metastable phases, superconducting excitations, and spin Hall effects
(SHE) is still lacking. Herein, we carry out a global structure search
in the Nb-B system based on the evolutionary algorithm and density
functional theory. Thermodynamical, dynamical, mechanical, and quasiharmonic
approximation investigations unveil four new phases, Nb3B5, Nb2B5, Nb3B7, and Nb5B4, which are promising candidates
for experimental preparations. Moreover, the superconducting transitions
of all Nb-B compounds are performed from electron–phonon calculations.
In addition, all Nb-B compounds are predicted to be topologically
nontrivial. More intriguingly, Nb2B5 is unveiled
as a promising noncentrosymmetric superconductor to explore topological
superconducting excitation. Furthermore, nonzero spin Hall conductivity
(SHC) tensor elements of all Nb-B compounds are predicted, and NbB
is predicted to own a maximal SHC value of 320 (ℏ/e) (S/cm) among all Nb-B compounds. Our theoretical results fill in
the gap on superconducting and SHC parameters of Nb-B binaries, demonstrating
that Nb-B binaries are a potential choice to explore superconducting
excitations and topological states and to investigate the SHE.