Syntheses and Crystal Structures of Two AlxRE3(Si1-yAly)S7 (RE =Sm and Gd) Compounds

摘要

Two new quaternary rare-earth chalcogenides,Al_(0.42)Sm_3(Si_(0.74)Al_(0.26))S_7(1) and Al_(0.38)Gd_3(Si_(0.86)Al_(0.14))S_7(2),have been synthesized by a facile solid-state route with boron as the reducing reagent.They crystallize in the noncentrosymmetric hexagonal space group P6_3,belonging to the Ce_6Al_(3.33)S_(14) structure-type.Their 3-D structures feature 3-D frameworks constructed by RES_8 bicapped trigonal prisms,and Al and Si occupy the octahedral and tetrahedral voids,respectively.Al(2) and Si(1) co-occupying the 2b site and Al(1) partially occupying the 2a site have to be considered for the stability of the structures and charge balances.The Ce_6Al_(3.33)S_(14) structure-type compounds with their rich compositions and traits are discussed.The diffuse reflectance spectrum measurement of 2 indicates that it has an energy gap of 2.13 eV.