Novel high pressure structures and superconductivity of niobium disulfide

Zhong-Li Liu; Ling-Cang Cai; Xiu-Lu Zhang

doi:10.1016/j.jallcom.2014.05.013

paper

Novel high pressure structures and superconductivity of niobium disulfide

arXiv:1401.3398 · doi:10.1016/j.jallcom.2014.05.013

Abstract

We have investigated the pressure-induced phase transition and superconducting properties of niobium disulfide (NbS $_{2}$ ) based on the density functional theory. The structures of NbS $_{2}$ at pressures from 0 to 200 GPa were predicted using the multi-algorithm collaborative (MAC) structure prediction technique. The previously known 1 $T$ -, 2 $H$ -, and 3 $R$ -NbS $_{2}$ were successfully reproduced. In addition, many metastable structures which are potential to be synthesized were also discovered. Based on the enthalpy calculations, we found that at 26 GPa NbS $_{2}$ transits from the double-hexagonal (2 $H$ ) structure to the tetragonal $I 4/ mmm$ structure with a $10.6%$ volume reduction. The calculated elastic constants and phonon dispersion curves of $I 4/ mmm$ -NbS $_{2}$ confirm its mechanical and dynamical stability at high pressure. More interestingly, the coordination number of Nb in $I 4/ mmm$ structure is eight which is larger than that in the traditional metal dichalcogenides, indicating a new type of bondings of Nb and S atoms. In the new Nb-S bondings, one Nb atom and neighboring eight S atoms form a [NbS $_{8}$ ] hexahedron unit. Furthermore, $I 4/ mmm$ -NbS $_{2}$ exhibits a higher superconducting critical temperature than 2 $H$ -NbS $_{2}$ , as is resulted from the stronger electron-phonon coupling coefficients

7 pages, 9 figures

Novel high pressure structures and superconductivity of niobium disulfide

Abstract

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