Formation of a Polar Structure in the Metallic Niobium Sulfide Nb4S3

The synthesis of Nb4S3, a previously undiscovered binary sulfide, was achieved using Nb3Br7S as a precursor. Its structure is composed of Nb6S triangular prisms arranged in a polar (Imm2) configuration, with sulfur atoms lying in channels along the a axis. Electrical resistivity measurements and density functional theory calculations were used to determine that Nb4S3 is metallic and therefore a polar metal, with metallic bands occupied by electrons with primarily niobium character. The electrons near the Fermi level are so closely associated with the niobium sublattice that the sulfur atoms have positive Born effective charges, indicating that the electrostatic interactions between sulfur atoms are unscreened. Calculations of the dependence of the electron density on the sulfur atomic positions confirm that the metallic electrons do not screen the dipole-dipole interactions between sulfur atoms, which allows polarity and metallicity to coexist in Nb4S3. These findings suggest that applied electric fields might be able to reverse the polarity of thin films of Nb4S3.

Automated summary

The synthesis of the previously undiscovered binary sulfide Nb4S3 using Nb3Br7S precursor has revealed it to be a polar metal, with metallic bands primarily occupied by electrons of niobium character. The unscreened electrostatic interactions between sulfur atoms in Nb4S3 allow for the coexistence of polarity and metallicity. These findings suggest that applied electric fields could potentially reverse the polarity of Nb4S3 thin films.