Flux Crystal Growth, Structure, and Optical Properties of LiLaTiSO: An Oxysulfide Phase Derived from KNiF-Type Structure.

Single crystals of a new titanium oxysulfide, LiLaTiSO, were grown from a KI molten salt. Single-crystal X-ray diffraction analysis revealed that LiLaTiSO crystallizes in the space group with lattice parameters of = 11.7319(4) Å, = 3.94787(14) Å, and = 20.6885(6) Å. In this structure, the one-dimensional chains of corner-sharing TiOS octahedra are further corner-linked via equatorial and apical oxygen atoms to form unique corrugated two-dimensional perovskite-type layers in the plane with one octahedral thickness. These layers were intervened along the -axis by the LaS rock-salt layers corrugated concomitantly with the perovskite-type layers, and LiOS tetrahedral chains were located between these two types of two-dimensional layers. LiLaTiSO can be viewed as a modified KNiF-type structure with TiOS octahedral layers stacked in a zigzag manner along the 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 orbitals, and the valence band maximum consists of S 3 O 2, and Li 2s orbitals. The electronic structures near the Fermi level are similar to those of the structurally related photocatalytic oxysulfides YTiSO and LaTiCuSO.