Crystal and electronic structures, and optical and magnetic properties of novel rare-earth sulfide borates RE3S3BO3 (RE = Sm, Gd)

Abstract

Two isostructural quaternary rare-earth sulfide borates Gd₃S₃BO₃ (1) and Sm₃S₃BO₃ (2) were synthesized by a high temperature solid-state method. They crystallize in the triclinic space group P and represent a rarely studied structure type. Their structures feature a 1D infinite {[RE₆(BO₃)₂]¹²⁺}_∞ chain constructed by the connection between RE ions and trigonal planar unit (BO₃)³⁻ anions, and S atoms occupying the trigonal bipyramid or tetragonal pyramid inter-spaces between the {[RE₆(BO₃)₂]¹²⁺}_∞ chains. Their structures can be recognized as a 1 : 1 intergrowth of Gd₂S₃- and Gd(BO₃)-like slabs, and this trait of the crystal chemistry is discussed. The optical energy gap of 1 is determined to be 2.65 eV, which is consistent with the result of the theoretical calculation. The calculation indicates that 1 is an indirect semiconductor, and its optical absorption is mainly ascribed to the charge transition from the S 3p to Gd 5d states. Compound 1 demonstrates antiferromagnetic behavior under low temperatures and orders at around 5.9 K, while 2 behaves with typical Van Vleck-type paramagnetism.