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Synthesis and characterization of 3D topological insulators: a case TlBi(S 1 − x Se x ) 2

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ABSTRACT

In this article, practical methods for synthesizing Tl-based ternary III-V-VI2 chalcogenide TlBi(SSex)2 are described in detail, along with characterization by x-ray diffraction and charge transport properties. The TlBi(SSex)2 system is interesting because it shows a topological phase transition, where a topologically nontrivial phase changes to a trivial phase without changing the crystal structure qualitatively. In addition, Dirac semimetals whose bulk band structure shows a Dirac-like dispersion are considered to exist near the topological phase transition. The technique shown here is also generally applicable for other chalcogenide topological insulators, and will be useful for studying topological insulators and related materials.

No MeSH data available.


Crystal structure of TlBiSe2. Hexagonal unit cell is shown by black thin lines, and the rhombohedral unit cell is shown by gray thick lines [34].
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Figure 1: Crystal structure of TlBiSe2. Hexagonal unit cell is shown by black thin lines, and the rhombohedral unit cell is shown by gray thick lines [34].

Mentions: Figure 1 shows the structure of TlBiSe2, which is called an NaFeO2-type. The crystallographic structure was first reported for TlBiTe2 in 1961 [28], and the structures of TlBiSe2 and TlBiS2 are essentially identical. The space group is R m (No. 166), which is the same as for other Z2 topological insulators such as BiSbx, Bi2Se3, and tetradymite families such as GeBi2Te4, etc. BiSbx takes a face-centered cubic (fcc)-like lattice structure distorted along the (111) direction. The unit structure of tetradymite is similar to that of TlBiSe2 and TlBiS2, but it continues for only five layers like Se-Bi-Se-Bi-Se because of the charge neutrality. In the TlBiSe2 and TlBiS2, Tl+ and Bi3+ align alternately, the averaged valence of the cations is +2, and charge neutrality is naturally conserved. Therefore, the structure of TlBiSe2 and TlBiS2 can be understood as a distorted NaCl-type, in which Tl+ and Bi3+ are alternately placed at the cation sites. The lattice constants were given in multiple papers [30–33], and the results are essentially consistent. Please note that the number of independent parameters is two, and thus the parameters of the hexagonal unit cell can be converted into a rhombohedral unit-cell expression, and vice versa. The conversion formulae are shown in the appendix.


Synthesis and characterization of 3D topological insulators: a case TlBi(S 1 − x Se x ) 2
Crystal structure of TlBiSe2. Hexagonal unit cell is shown by black thin lines, and the rhombohedral unit cell is shown by gray thick lines [34].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036500&req=5

Figure 1: Crystal structure of TlBiSe2. Hexagonal unit cell is shown by black thin lines, and the rhombohedral unit cell is shown by gray thick lines [34].
Mentions: Figure 1 shows the structure of TlBiSe2, which is called an NaFeO2-type. The crystallographic structure was first reported for TlBiTe2 in 1961 [28], and the structures of TlBiSe2 and TlBiS2 are essentially identical. The space group is R m (No. 166), which is the same as for other Z2 topological insulators such as BiSbx, Bi2Se3, and tetradymite families such as GeBi2Te4, etc. BiSbx takes a face-centered cubic (fcc)-like lattice structure distorted along the (111) direction. The unit structure of tetradymite is similar to that of TlBiSe2 and TlBiS2, but it continues for only five layers like Se-Bi-Se-Bi-Se because of the charge neutrality. In the TlBiSe2 and TlBiS2, Tl+ and Bi3+ align alternately, the averaged valence of the cations is +2, and charge neutrality is naturally conserved. Therefore, the structure of TlBiSe2 and TlBiS2 can be understood as a distorted NaCl-type, in which Tl+ and Bi3+ are alternately placed at the cation sites. The lattice constants were given in multiple papers [30–33], and the results are essentially consistent. Please note that the number of independent parameters is two, and thus the parameters of the hexagonal unit cell can be converted into a rhombohedral unit-cell expression, and vice versa. The conversion formulae are shown in the appendix.

View Article: PubMed Central - PubMed

ABSTRACT

In this article, practical methods for synthesizing Tl-based ternary III-V-VI2 chalcogenide TlBi(SSex)2 are described in detail, along with characterization by x-ray diffraction and charge transport properties. The TlBi(SSex)2 system is interesting because it shows a topological phase transition, where a topologically nontrivial phase changes to a trivial phase without changing the crystal structure qualitatively. In addition, Dirac semimetals whose bulk band structure shows a Dirac-like dispersion are considered to exist near the topological phase transition. The technique shown here is also generally applicable for other chalcogenide topological insulators, and will be useful for studying topological insulators and related materials.

No MeSH data available.