Synthesis, structural and spectroscopic properties of orthorhombic compounds BaLnCuS3 (Ln = Pr, Sm)

Abstract

Ternary sulfides BaPrCuS3 and BaSmCuS3 are first synthesized by the sulphidation reaction of a mixture of related oxides and metal Cu in a flow of (CS2, H2S) at 1170 K. The crystal structures of BaPrCuS3 and BaSmCuS3 are obtained by Rietveld method. BaPrCuS3 crystallizes in space group Pnma with unit cell parameters a = 10.56074(6), b = 4.11305(2) and c = 13.42845(7) Å, V = 583.289 (5) Å3, Z = 2. BaSmCuS3 crystallizes in space group Cmcm with unit cell parameters a = 4.07269(4), b = 13.4499(1) and c = 10.3704(1) Å, V = 568.06 (1) Å3, Z = 2. The structural model is proposed for the Cmcm→Pnma transition in compounds ABCX3 (X = S, Se) for the sequence Sm-Pm-Nd-Pr. The dimensionless tolerance factor t = IR(A)IR(C)/IR(B)2 is suggested to control the boundary between the Cmcm and Pnma structures. The micromorphological, thermal and spectroscopic properties are evaluated for BaPrCuS3. The compound melts incongruently at Tmelt = 1580.9 K. In BaPrCuS3, the band gap is estimated to be 2.1 eV. The vibrational parameters of BaPrCuS3 and BaSmCuS3 are comparatively observed by Raman spectroscopy.