One-dimensional Anisotropic Electronic States in Needle-shaped La5Ti2CuS5O7 Single Crystals Grown in Molten Salt in Bridgman Furnace

High-quality needle-like crystals of La5Ti2CuS5O7 (a ternary transition-metallic oxysulfide) as long as 1 mm and a few μm in diameter were grown in CsCl molten-salt flux. This synthesis process was performed in a Bridgman furnace with slow motion of charge across the heating zone. Transmission electron microscopy/diffraction analysis indicated that they are product crystallites without crystalline intergrowth, and that the longitudinal direction of needle crystals is parallel to crystallographic b axis of La5Ti2CuS5O7. Optical polarized ultraviolet–visible reflectance spectroscopy provided the first experimental evidence of the one-dimensional electronic excitation along the b axis of this material. The spectroscopic peaks are assigned to the transitions between the electronic bands aided by numerical calculations on the basis of density functional theory (DFT). The advantages of this synthetic process will be applicable in general for oxysulfides that are useful as optical and photocatalytic materials.