Synthesis of ternary rare-earth sulfides LnGdS3 (Ln: Nd and Sm)

We have developed a route to synthesize the ternary rare-earth sulfides LnGdS₃ (Ln: Nd and Sm). The aqueous solutions of citric acid and rare-earth nitrates Ln(NO₃)₃ and Gd(NO₃)₃ were stirred at about 333 K for 2-3 h to promote the formation of complexes. Those complexes were polymerized by ethylene glycol at about 393 K for 2 h to polymer gels, and then calcined at 623 K for 2 h. When the precursors formed were crystallized at 773 K for 2 h in air, the products consisted of the oxycarbonates LnGdO₂CO₃. The orthorhombic LnGdS₃ powders were synthesized by the sulfurization of the oxycarbonates with carbon disulfide at 1073 K for 8 h. After pressure-assisted sintering at 1573-1773 K for 1 h, the orthorhombic LnGdS₃ phase was transformed into the cubic LnGdS₃ phase.