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TlSe is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Tl1+ is bonded in a body-centered cubic geometry to eight equivalent Se1- atoms. All Tl–Se bond lengths are 3.25 Å. Se1- is bonded in a body-centered cubic geometry to eight equivalent Tl1+ atoms.
TlSe is I4/mcm structured and crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded in a 10-coordinate geometry to eight equivalent Se1- atoms. All Tl–Se bond lengths are 3.53 Å. In the second Tl1+ site, Tl1+ is bonded to four equivalent Se1- atoms to form edge-sharing TlSe4 tetrahedra. All Tl–Se bond lengths are 2.73 Å. Se1- is bonded in a 2-coordinate geometry to six Tl1+ atoms.
Analogous to 2D layered transition-metal dichalcogenides, the TlSe family of quasi-one dimensional chain materials with the Zintl-type structure exhibits novel phenomena under high pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe 2 using Raman spectroscopy, synchrotron X-ray diffraction (XRD), and transport measurements, in combination with first principles crystal structure prediction (CSP) based on evolutionary approach. We found that TlInTe2 undergoes a pressure-induced semiconductor-to-semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with T c = 3.8 K). An unusual giant phonon mode (A g ) softening appears at ~10–12 GPa as a result of the interaction of optical phonons with the conduction electrons. The high-pressure XRD and Raman spectroscopy studies reveal that there is no structural phase transitions observed up to the maximum pressure achieved (33.5 GPa), which is in agreement with our CSP calculations. In addition, our calculations predict two high-pressure phases above 35 GPa following the phase transition sequence as I4/mcm (B37) → Pbcm → Pm$\bar{3}$m (B2). Electronic structure calculations suggest Lifshitz (L1 & L2-type) transitions near the superconducting transition pressure. Furthermore, our findings on TlInTe 2 open up a new avenue to study unexplored high-pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), giant phonon softening, and electron–phonon coupling.