Regularities of the property changes in the compounds EuLnCuS3 (Ln = La-Lu)

This work contains the results of complex experimental research of the compounds EuLnCuS(3) (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 EuLnCuS(3) (Ln = Sm, Gd-Lu): for EuSmCuS3 T-alpha <->beta = 1437 K, Delta H-alpha <->beta = 7.0 kJ.mol(-1), T-beta <->gamma = 1453 K, Delta H-beta <->gamma = 2.6 kJ.mol(-1); for EuTbCuS3 T-alpha <->beta = 1478 K, Delta H-alpha <->beta = 1.6 kJ.mol(-1), T-beta <->gamma = 1516 K, Delta H-beta <->gamma = 0.9 kJ.mol(-1), T-gamma <->delta = 1548 K, Delta H-gamma <->delta = 1.6 kJ.mol(-1); for EuTmCuS3 T-alpha <->beta = 1543 K, T-beta <->gamma = 1593 K, T-gamma <->delta = 1620 K; for EuYbCuS3 T-alpha <->beta = 1513 K, T-beta <->gamma = 1564 K, T-gamma <->delta = 1594 K; for EuLuCuS3 T-alpha <->beta = 1549 K, T-beta <->gamma = 1601 K, T-gamma <->delta = 1628 K. In the EuLnCuS(3) 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 rLn(3+) as well as influencing of phenomenon of crystallochemical contraction were observed. For delimiting between space groups Cmcm and Pnma in the compounds ALnCuS(3), the use of the tolerance factor t' = IR(A)center dot IR(C) + axIR(B)(2) was verified. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This work investigated the compounds EuLnCuS(3) (Ln = La-Lu) through complex experimental research and DFT calculations, focusing on vibrational modes, elastic properties, and polymorphous transitions. Despite the narrow temperature range, ferro- or ferrimagnetic states were observed in the EuLnCuS(3) series. The study also highlighted the tetrad effect in the changes of melting temperature and microhardness, as well as the influence of crystallochemical contraction phenomenon.