Synthesis and structures of new ternary aluminum chalcogenides:: LiAlSe2, α-LiAlTe2, and β-LiAlTe2

The synthesis and crystal structures of new ternary aluminum chalcogenides, LiAlSe2, alpha-LiAlTe2, and beta-LiAlTe2, are reported. These compounds are synthesized by solid-state reaction at 800 degrees C. The single-crystal X-ray structures of these compounds have been determined. LiAlSe2: a = 6.8228(9) Angstrom, b = 8.266(1) Angstrom, c = 6.5236(7) Angstrom, Pna2(1) (No. 33, Z = 4). alpha-LiAlTe2: a = 6.5317(4) Angstrom, c = 11.6403(9) Angstrom, I (4) over bar 2d (No. 122, Z = 4). beta-LiAlTe2: a = 4.4810(6) Angstrom, c = 7.096(1) Angstrom, P3m1 (No. 156, Z = 1). These ternary compounds are formed by fusion of AlQ(4) (Q = Se, Te) tetrahedra. LiAlSe2 shows beta-NaFeO2 structure type, which can be viewed as a wurtzite superstructure. alpha-LiAlTe2 adopts chalcopyrite structure type. In LiAlSe2 and alpha-LiAlTe2, AlQ(4) (Q = Se, re) tetrahedra share four corners to build three-dimensional structures and Li atoms are located in the tetrahedral sites between the chalcogen layers. beta-LiAlTe2 has polar layers formed by three-corner shared AlTe4 tetrahedra, and Li cations are in the distorted antiprisms between the layers. Li-7 MAS NMR studies show that chemical shifts of Li in these ternary chalcogenides are nearly identical regardless of different chemical environments.