Laboratory of Theory and Optimization of Chemical and Technological Processes, University of Tyumen, 625003 Tyumen, Russia.
Institute of Chemistry and Chemical Technology, Federal Research Center KSC SB RAS, 660036 Krasnoyarsk, Russia.
Int J Mol Sci. 2022 Jan 28;23(3):1503. doi: 10.3390/ijms23031503.
In this work, we report on the synthesis, in-depth crystal structure studies as well as optical and magnetic properties of newly synthesized heterometallic quaternary selenides of the EuLnCuSe composition. Crystal structures of the obtained compounds were refined by the derivative difference minimization (DDM) method from the powder X-ray diffraction data. The structures are found to belong to orthorhombic space groups (structure type BaMnS for EuLaCuSe and structure type EuCuS for EuLnCuSe, where Ln = Sm, Gd, Tb, Dy, Ho and Y) and (structure type KZrCuS for EuLnCuSe, where Ln = Tm, Yb and Lu). Space groups and were delimited based on the tolerance factor t', and vibrational spectroscopy additionally confirmed the formation of three structural types. With a decrease in the ionic radius of Ln in the reported structures, the distortion of the (LnCuSe) layers decreases, and a gradual formation of the more symmetric structure occurs in the sequence BaMnS → EuCuS → KZrCuS. According to magnetic studies, compounds EuLnCuSe (Ln = Tb, Dy, Ho and Tm) each exhibit ferrimagnetic properties with transition temperatures ranging from 4.7 to 6.3 K. A negative magnetization effect is observed for compound EuHoCuSe at temperatures below 4.8 K. The magnetic properties of the discussed selenides and isostructural sulfides were compared. The direct optical band gaps for EuLnCuSe, subtracted from the corresponding diffuse reflectance spectra, were found to be 1.87-2.09 eV. Deviation between experimental and calculated band gaps is ascribed to lower states of Eu in the crystal field of EuLnCuSe, while anomalous narrowing of the band gap of EuYbCuSe is explained by the low-lying charge-transfer state. Ab initio calculations of the crystal structures, elastic properties and phonon spectra of the reported compounds were performed.
在这项工作中，我们报告了新合成的 EuLnCuSe 组成的异金属四元硒化物的合成、深入的晶体结构研究以及光学和磁性性质。通过粉末 X 射线衍射数据的导数差最小化（DDM）方法对获得的化合物的晶体结构进行了精修。发现这些结构属于正交晶系空间群 （结构类型为 BaMnS，EuLaCuSe；结构类型为 EuCuS，EuLnCuSe，其中 Ln = Sm、Gd、Tb、Dy、Ho 和 Y）和 （结构类型为 KZrCuS，EuLnCuSe，其中 Ln = Tm、Yb 和 Lu）。根据容忍因子 t'，限定了空间群 和 ，振动光谱进一步证实了三种结构类型的形成。在所报道的结构中，随着 Ln 离子半径的减小，（LnCuSe）层的变形减小，并且在 BaMnS→EuCuS→KZrCuS 的顺序中逐渐形成更对称的结构。根据磁性研究，化合物 EuLnCuSe（Ln = Tb、Dy、Ho 和 Tm）各自表现出铁磁性质，转变温度范围为 4.7 至 6.3 K。化合物 EuHoCuSe 在低于 4.8 K 的温度下表现出负磁化效应。比较了讨论的硒化物和等结构的硫化物的磁性。从相应的漫反射光谱中减去 EuLnCuSe 的直接光学带隙，发现为 1.87-2.09 eV。实验和计算带隙之间的偏差归因于 EuLnCuSe 晶体场中 Eu 的较低 态，而 EuYbCuSe 带隙的异常变窄则归因于低位的电荷转移态。对所报道化合物的晶体结构、弹性性质和声子谱进行了从头算计算。
