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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.
Ti(TlSe)4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ti4+ is bonded in a tetrahedral geometry to four Se2- atoms. There are a spread of Ti–Se bond distances ranging from 2.40–2.42 Å. There are four inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.10–3.93 Å. In the second Tl1+ site, Tl1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.13–3.91 Å. In the third Tl1+ site, Tl1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.07–3.83 Å. In the fourth Tl1+ site, Tl1+ is bonded in a 4-coordinate geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.10–3.58 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to one Ti4+ and four Tl1+ atoms to form distorted corner-sharing SeTiTl4 trigonal bipyramids. In the second Se2- site, Se2- is bonded in a 1-coordinate geometry to one Ti4+ and four Tl1+ atoms. In the third Se2- site, Se2- is bonded in a 1-coordinate geometry to one Ti4+ and six Tl1+ atoms. In the fourth Se2- site, Se2- is bonded in a 1-coordinate geometry to one Ti4+ and six Tl1+ atoms.
Zr(TlSe)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded to six Se2- atoms to form ZrSe6 octahedra that share corners with four TlSe5 square pyramids, edges with two ZrSe6 octahedra, and edges with six TlSe5 square pyramids. There are a spread of Zr–Se bond distances ranging from 2.68–2.82 Å. In the second Zr4+ site, Zr4+ is bonded to six Se2- atoms to form ZrSe6 octahedra that share corners with four TlSe5 square pyramids, edges with two ZrSe6 octahedra, and edges with six TlSe5 square pyramids. There are a spread of Zr–Se bond distances ranging from 2.68–2.83 Å. In the third Zr4+ site, Zr4+ is bonded to six Se2- atoms to form ZrSe6 octahedra that share corners with four TlSe5 square pyramids, edges with two equivalent ZrSe6 octahedra, and edges with six TlSe5 square pyramids. There are two shorter (2.73 Å) and four longer (2.76 Å) Zr–Se bond lengths. There are ten inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two equivalent ZrSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three ZrSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 14–18°. There are a spread of Tl–Se bond distances ranging from 3.03–3.46 Å. In the second Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two ZrSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three ZrSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 7–9°. There are a spread of Tl–Se bond distances ranging from 3.07–3.44 Å. In the third Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.01–3.33 Å. In the fourth Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two ZrSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three ZrSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 10–11°. There are a spread of Tl–Se bond distances ranging from 3.05–3.50 Å. In the fifth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.03–3.42 Å. In the sixth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.02–3.46 Å. In the seventh Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two ZrSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three ZrSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 10–14°. There are a spread of Tl–Se bond distances ranging from 3.03–3.43 Å. In the eighth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 2.99–3.35 Å. In the ninth Tl1+ site, Tl1+ is bonded in a rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.01–3.47 Å. In the tenth Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two ZrSe6 octahedra, edges with three ZrSe6 octahedra, and edges with four TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 15–19°. There are a spread of Tl–Se bond distances ranging from 3.04–3.46 Å. There are ten inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to one Zr4+ and five Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeZrTl5 octahedra. The corner-sharing octahedra tilt angles range from 8–17°. In the second Se2- site, Se2- is bonded to two equivalent Zr4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeZr2Tl4 octahedra. The corner-sharing octahedra tilt angles range from 5–19°. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to two Zr4+ and four Tl1+ atoms. In the fourth Se2- site, Se2- is bonded to two Zr4+ and four Tl1+ atoms to form distorted SeZr2Tl4 octahedra that share corners with three SeZrTl5 octahedra and edges with six SeZr2Tl4 octahedra. The corner-sharing octahedra tilt angles range from 0–16°. In the fifth Se2- site, Se2- is bonded in a 6-coordinate geometry to one Zr4+ and five Tl1+ atoms. In the sixth Se2- site, Se2- is bonded to two Zr4+ and four Tl1+ atoms to form distorted SeZr2Tl4 octahedra that share corners with three SeZrTl5 octahedra and edges with eight SeZr2Tl4 octahedra. The corner-sharing octahedra tilt angles range from 8–17°. In the seventh Se2- site, Se2- is bonded in a 6-coordinate geometry to one Zr4+ and five Tl1+ atoms. In the eighth Se2- site, Se2- is bonded to one Zr4+ and five Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeZrTl5 octahedra. The corner-sharing octahedra tilt angles range from 8–16°. In the ninth Se2- site, Se2- is bonded to one Zr4+ and five Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeZrTl5 octahedra. The corner-sharing octahedra tilt angles range from 0–19°. In the tenth Se2- site, Se2- is bonded to two Zr4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeZr2Tl4 octahedra. The corner-sharing octahedra tilt angles range from 5–14°.
Hf(TlSe)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six Se2- atoms to form HfSe6 octahedra that share corners with three TlSe5 square pyramids, edges with two HfSe6 octahedra, and edges with six TlSe5 square pyramids. There are a spread of Hf–Se bond distances ranging from 2.66–2.78 Å. In the second Hf4+ site, Hf4+ is bonded to six Se2- atoms to form HfSe6 octahedra that share corners with four TlSe5 square pyramids, edges with two HfSe6 octahedra, and edges with four TlSe5 square pyramids. There are a spread of Hf–Se bond distances ranging from 2.65–2.79 Å. In the third Hf4+ site, Hf4+ is bonded to six Se2- atoms to form HfSe6 octahedra that share corners with two equivalent TlSe5 square pyramids, edges with two equivalent HfSe6 octahedra, and edges with four TlSe5 square pyramids. There are a spread of Hf–Se bond distances ranging from 2.70–2.74 Å. There are ten inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two equivalent HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and an edgeedge with one TlSe5 square pyramid. The corner-sharing octahedra tilt angles range from 15–18°. There are a spread of Tl–Se bond distances ranging from 3.02–3.49 Å. In the second Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 7–9°. There are a spread of Tl–Se bond distances ranging from 3.08–3.48 Å. In the third Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.01–3.34 Å. In the fourth Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and edges with two TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 10–11°. There are a spread of Tl–Se bond distances ranging from 3.05–3.53 Å. In the fifth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.04–3.46 Å. In the sixth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.02–3.51 Å. In the seventh Tl1+ site, Tl1+ is bonded to five Se2- atoms to form distorted TlSe5 square pyramids that share corners with two HfSe6 octahedra, corners with two equivalent TlSe5 square pyramids, edges with three HfSe6 octahedra, and edges with three TlSe5 square pyramids. The corner-sharing octahedra tilt angles range from 11–15°. There are a spread of Tl–Se bond distances ranging from 3.03–3.45 Å. In the eighth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.00–3.36 Å. In the ninth Tl1+ site, Tl1+ is bonded in a distorted rectangular see-saw-like geometry to four Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.01–3.50 Å. In the tenth Tl1+ site, Tl1+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.05–3.50 Å. There are ten inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the second Se2- site, Se2- is bonded to two equivalent Hf4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHf2Tl4 octahedra. The corner-sharing octahedra tilt angles range from 12–20°. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to two Hf4+ and four Tl1+ atoms. In the fourth Se2- site, Se2- is bonded to two Hf4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHf2Tl4 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifth Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the sixth Se2- site, Se2- is bonded to two Hf4+ and four Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHf2Tl4 octahedra. The corner-sharing octahedral tilt angles are 12°. In the seventh Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the eighth Se2- site, Se2- is bonded in a 6-coordinate geometry to one Hf4+ and five Tl1+ atoms. In the ninth Se2- site, Se2- is bonded to one Hf4+ and five Tl1+ atoms to form a mixture of distorted edge and corner-sharing SeHfTl5 octahedra. The corner-sharing octahedra tilt angles range from 0–20°. In the tenth Se2- site, Se2- is bonded in a 6-coordinate geometry to two Hf4+ and four 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.