Synthesis, structure, and properties of EuErCuS3

Abstract

The crystal structure of the first-synthesized compound EuErCuS3 was determined from X-ray powder diffraction data: orthorhombic crystal system, space group Pnma, structural type Eu2CuS3: a = 10.1005(2) Å, b = 3.91255(4)Å, c = 12.8480(2) Å; V = 507.737(14) Å3, Z = 4, and ρx = 6.266 g/cm3. The temperatures and enthalpies of reversible polymorphic transitions and incongruent melting of the compound were determined by DSC: Tα↔β = 1524 K, ΔНα↔β = 2.3 ± 0.2 kJ∙mol−1; Tβ↔γ = 1575 K, ΔНβ↔γ = 0.7 ± 0.1 kJ∙mol−1; Tγ↔δ = 1602 K; ΔНγ↔δ = 1.3 ± 0.1 kJ∙mol−1 and Tcr = 1735 ± 10 K, ΔНcr = −3.5 ± 0.3 kJ∙mol−1. IR spectra were recorded in the range from 50 to 400 cm−1. The compound was found to be IR-transparent in the range 4000–400 cm−1. The compound was characterized by Raman spectroscopy. The observed spectra featured both Raman lines and luminescence. Ab initio calculations of the EuErCuS3 crystal structure and phonon spectrum were performed, the frequencies and types of fundamental modes were determined, and the involvement of constituent ions in the IR and Raman modes was assessed from an analysis of the ab initio displacement vectors. The vibrational spectra were interpreted. EuErCuS3 manifests a ferrimagnetic transition at 4.8 K. Its microhardness is 2850 MPa. The obtained data can serve as the basis for predicting the properties of EuLnCuS3 compounds. Valence states for Eu (2+) and Er (3+) are proved both by the XRD and optical methods. Optical band gap was found to be 1.934 eV from diffuse reflectance spectrum. © 2019 Elsevier B.V.