Synthesis, structure, magnetic and photoelectric properties of Ln3M0.5M′Se7 (Ln = La, Ce, Sm; M = Fe, Mn; M′ = Si, Ge) and La3MnGaSe7

Six new isostructural compounds, with the formulas La3Fe0.5GeSe7, La3MnGaSe7, Ce3Fe0.5SiSe7, Ce3Mn0.5SiSe7, Sm3Fe0.5SiSe7 and Sm3Mn0.5GeSe7, have been successfully synthesized via a molten salt method. Their structures are determined by single crystal X-ray diffraction and they crystallize in the Ce6Al3.33S14 structure type (space group: P6(3), Pearson symbol: hP24). Pure phases of the Ce3Fe0.5SiSe7, Ce3Mn0.5SiSe7, Sm3Fe0.5SiSe7 and Sm3Mn0.5GeSe7 compounds were obtained by solid state reaction and were characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), ultraviolet-visible-infrared (UV-vis-IR) absorbance spectroscopy, and magnetization measurements. The Ce3Fe0.5SiSe7 and Ce3Mn0.5SiSe7 compounds show paramagnetic domination accompanied by antiferromagnetic contributions, while the Sm3Mn0.5GeSe7 and Sm3Fe0.5SiSe7 compounds show antiferromagnetic phase transitions with Neel temperatures of 13 K and 24 K, respectively. Optical measurements reveal that all of the four compounds can absorb most of visible light. These four compounds also show photoelectric properties with the photocurrent densities of 81, 1.3, 1.8 and 0.8 mu A cm(-2), respectively.