Flux Crystal Growth, Structure, and Optical Properties of LiLa 3 Ti 2 S 3 O 6 : An Oxysulfide Phase Derived from K 2 NiF 4 -Type Structure.

Single crystals of a new titanium oxysulfide, LiLa 3 Ti 2 S 3 O 6 , were grown from a KI molten salt. Single-crystal X-ray diffraction analysis revealed that LiLa 3 Ti 2 S 3 O 6 crystallizes in the space group Pnma with lattice parameters of a = 11.7319(4) Å, b = 3.94787(14) Å, and c = 20.6885(6) Å. In this structure, the one-dimensional chains of corner-sharing TiO 5 S octahedra are further corner-linked via equatorial and apical oxygen atoms to form unique corrugated two-dimensional perovskite-type layers in the ab plane with one octahedral thickness. These layers were intervened along the c -axis by the LaS rock-salt layers corrugated concomitantly with the perovskite-type layers, and LiO 2 S 2 tetrahedral chains were located between these two types of two-dimensional layers. LiLa 3 Ti 2 S 3 O 6 can be viewed as a modified K 2 NiF 4 -type structure with TiO 5 S octahedral layers stacked in a zigzag manner along the c axis. The oxysulfide has a direct-type band gap of 1.85 eV, based on UV-vis-NIR diffuse reflectance measurements. First-principles calculations showed that the conduction band minimum mainly consists of Ti 3 d orbitals, and the valence band maximum consists of S 3 p, O 2 p , and Li 2s orbitals. The electronic structures near the Fermi level are similar to those of the structurally related photocatalytic oxysulfides Y 2 Ti 2 S 2 O 5 and La 5 Ti 2 CuS 5 O 7 .