Optical, Photoelectric, and Electrocatalytic Properties of Quaternary Sulfides RE ₃ M _{1– x} SnS ₇ ( RE = La–Nd; M = Ti–Cu, Cd)

Several series of quaternary sulfides RE 3 M 1– x SnS 7 ( RE = La–Nd; M = Ti–Cu, Cd) were synthesized by direct reaction of the elements at 1000 °C and their crystal structures were determined by powder X-ray diffraction, as well as single-crystal X-ray diffraction for many members. Most adopt the noncentrosymmetric La 3 Mn 0.5 SiS 7 -type structure (hexagonal, space group P 6 3 ) consisting of one-dimensional stacks of Sn-centered tetrahedra and columns of face-sharing M -centered octahedra. With focus placed on the La-containing series La 3 M 1– x SnS 7, further characterization was performed using X-ray photoelectron and electron paramagnetic spectroscopy. Their optical band gaps ranged from 1.5 to 2.5 eV. Selected members of this series were evaluated for various functional properties. La 3 Mn 0.5 SnS 7 and La 3 Cd 0.5 SnS 7 show moderate second harmonic generation at 1800 nm but high laser-induced damage thresholds and improved figures of merit relative to benchmark infrared nonlinear optical materials. La 3 Fe 0.5 SnS 7 exhibits high photocurrent density suitable for photoelectric energy conversion. La 3 Ni 0.5 SnS 7 demonstrates electrocatalytic activity for the oxygen evolution reaction in water.