Regularities of the property changes in the compounds EuLnCuS(3) (Ln = La-Lu)
This work contains the results of complex experimental research of the compounds EuLnCuS3 (Ln = La-Lu) enhanced by the DFT calculations. It is aimed at the data replenishment with particular attention to the revelation of regularities in the property changes, in order to extend the potential applicability of the materials of the selected chemical class. The ab initio calculations of the fundamental vibrational modes of the crystal structures were in good agreement with experimental results. The wavenumbers and types of the modes were determined, and the degree of the ion participation in the modes was also estimated. The elastic properties of the compounds were calculated. The compounds were found out to be IR-transparent in the range of 4000–400 cm–1. The estimated microhardness of the compounds is in the range of 2.68–3.60 GPa. According to the DSC data, the reversible polymorphous transitions were manifested in the compounds EuLnCuS3 (Ln = Sm, Gd-Lu): for EuSmCuS3 Tα↔β = 1437 K, ΔНα↔β = 7.0 kJ·mol-1, Tβ↔γ = 1453 K, ΔНβ↔γ = 2.6 kJ·mol-1; for EuTbCuS3 Tα↔β = 1478 K, ΔНα↔β = 1.6 kJ·mol-1, Tβ↔γ = 1516 K, ΔНβ↔γ = 0.9 kJ·mol-1, Tγ↔δ = 1548 K, ΔНγ↔δ = 1.6 kJ·mol-1; for EuTmCuS3 Tα↔β = 1543 K, Tβ↔γ = 1593 K, Tγ↔δ = 1620 K; for EuYbCuS3 Tα↔β = 1513 K, Tβ↔γ = 1564 K, Tγ↔δ = 1594 K; for EuLuCuS3 Tα↔β = 1549 K, Tβ↔γ = 1601 K, Tγ↔δ = 1628 K. In the EuLnCuS3 series, the transition into either ferro- or ferrimagnetic states occurred in the narrow temperature range from 2 to 5 K. The tetrad effect in the changes of incongruent melting temperature and microhardness conditioned on rLn3+ as well as influencing of phenomenon of crystallochemical contraction were observed. For delimiting between space groups Cmcm and Pnma in the compounds ALnCuS3, the use of the tolerance factor t’ = IR(A)·IR(C) + a×IR(B)2 was verified.