Orthorhombic To Monoclinic Phase Transition In Nbnite2

The high-temperature structural phase transition of the potential topological material NbNiTe2 has been studied in detail. At high temperatures, the structure is centrosymmetric with orthorhombic space-group P 2/m 2/n 2(1)/a (Pmna), and distorts at 373 K to a monoclinic structure with space-group P11 2(1)/a (P112(1)/a). A small signature in specific heat and commensurate small release of entropy are observed at the phase transition. The low-temperature monoclinic structure retains its inversion center and the symmetries associated with the orthorhombic c axis. At high temperatures, NbNiTe2 shows phonon instabilities at Gamma and X, which are removed by the structural phase transition. The electronic structure of NbNiTe2 is only slightly affected, indicating this ferroic phase transition is primarily due to steric effects.