Syntheses and characterization of two new layered ternary chalcogenides NaScQ(2) (Q = Se and Te)

Two new mixed metal ternary chalcogenides, NaScSe2 and NaScTe2, have been synthesized by the high-temperature reaction of elements using the sealed tube method. Single crystal X-ray diffraction studies show that both compounds are isostructural and adopt the trigonal crystal system with space group R3m with three formula units (Z = 3). The NaScQ(2) structure consists of three unique crystallographic sites: Na, Sc, and Q sites. The Sc atom in this structure sits at the center of an octahedron of six Q atoms. The six Sc-Q bonds are identical, but the geometry of ScQ(6) is slightly distorted compared with the ideal octahedron. The ScQ(6) octahedra are conjoined to adjacent units via edge-sharing to form two-dimensional layers of 2(infinity)[ScQ(2)](1-). Two such layers are separated by the filling of Na+ cations, each surrounded by six Q atoms forming distorted octahedral geometry. These two chalcogenides are valence precise [Na1+Sc3+(Q(2-))(2)]. The optical absorption and thermal conductivity measurements were carried out on the polycrystalline samples of NaScQ(2). The optical bandgap value for NaScSe2 (1.5(1) eV) and NaScTe2 (1.2(1) eV) confirms their semiconducting nature. The high-temperature resistivity and Seebeck coefficient studies were also performed on a sintered polycrystalline sample of NaScTe2. The emission spectroscopic analysis of the polycrystalline NaScSe2 was also analyzed to understand the fluorescence properties. DFT calculations were performed to study the electronic structure, optical, and thermoelectric properties of NaScQ(2). The COHP analysis shows stronger chemical bonding between the Sc and Te atoms compared with that of Na atoms in the NaScQ(2) structure.

Automated summary

Two new mixed metal ternary chalcogenides, NaScSe2 and NaScTe2, were synthesized in this study. The compounds were found to be semiconductors with optical bandgap values confirming their nature. Several properties like optical absorption, thermal conductivity, and emission spectroscopic analysis were investigated, along with DFT calculations to study their electronic structure and chemical bonding properties.