Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

Experimental and Theoretical Insights on the Structural, Electronic, and Magnetic Properties of the Quaternary Selenides EuPrCuSe3 and EuNdCuSe3

Magnetic semiconductors EuPrCuSe3 and EuNdCuSe3 were obtained by using the halide flux method. Their crystal structures and magnetic properties were studied and discussed. Optical properties of the obtained selenides were studied by the means of diffuse reflectance spectroscopy, which revealed the values of 1.92/1.97 and 0.90/0.94 eV for the direct and indirect band gaps of Ln = Nd/Pr, respectively. The structural, electronic, and magnetic properties of the obtained compounds were additionally studied with spin-polarized density functional theory calculations, wherein both systems were found to be two new examples of semiconducting quaternary selenides with disperse conduction bands of Nd/Pr 5d character. The modeling showed that various magnetic orderings in the systems have subtle influences on the alignments/overlaps between the Se/Cu, Eu, and Pr/Nd bands, and that the spin-state energetics are very dependent upon the treatment of electron correlation, but a distinguishing feature in the case of ferromagnetic coupling is that the spin density on the Se atoms is maximized. Overall, the calculations are in good agreement with the experimental characterization of ferromagnetism in the bulk crystals, wherein the ferromagnetic transition occurs at temperatures of about 2.5 K for EuPrCuSe3 and about 3 K for EuNdCuSe3.

Synthesis, Crystal Structure, and Optical and Magnetic Properties of the New Quaternary Erbium Telluride EuErCuTe3: Experiment and Calculation

This paper reports for the first time on a new layered magnetic heterometallic erbium telluride EuErCuTe3. Single crystals of the compound were obtained from the elements at 1120 K using CsI as a flux. The crystal structure of EuErCuTe3 was solved in the space group Cmcm (a = 4.3086(3) Å, b = 14.3093(9) Å, and c = 11.1957(7) Å) with the KZrCuS3 structure type. In the orthorhombic structure of erbium telluride, distorted octahedra ([ErTe6]9-) form two-dimensional layers (Er(Te1)2/2e(Te2)4/2k-)∞2, while distorted tetrahedra ([CuTe4]7-) form one-dimensionally connected substructures (Cu(Te1)2/2e(Te2)2/1t5-∞1) along the [100] direction. The distorted octahedra and tetrahedra form parallel two-dimensional layers (CuErTe32-∞2) between which Eu2+ ions are located in a trigonal-prismatic coordination environment (EuTe610-). The trigonal prisms are connected by faces, forming chains (Eu(Te1)2/2(Te2)4/22-∞1) along the [100] direction. Regularities in the variations in structural parameters were established in the series of erbium chalcogenides (EuErCuCh3 with Ch = S, Se, and Te) and tellurides (EuLnCuTe3 with Ln = Gd, Er, and Lu). Ab-initio calculations of the crystal structure, phonon spectrum, and elastic properties of the compound EuErCuTe3 were performed. The types and wavenumbers of fundamental modes were determined, and the involvement of ions in the IR and Raman modes was assessed. The experimental Raman spectra were interpreted. The telluride EuErCuTe3 at temperatures below 4.2 K was ferrimagnetic, as were the sulfide and selenide derivatives (EuErCuCh3 with Ch = S and Se). Its experimental magnetic characteristics were close to the calculated ones. The decrease in the magnetic phase transition temperature in the series of the erbium chalcogenides was discovered.

Single Crystals of EuScCuSe3: Synthesis, Experimental and DFT Investigations

EuScCuSe₃ was synthesized from the elements for the first time by the method of cesium-iodide flux. The crystal belongs to the orthorhombic system (Cmcm) with the unit cell parameters a = 3.9883(3) Å, b = 13.2776(9) Å, c = 10.1728(7) Å, V = 538.70(7) ų. Density functional (DFT) methods were used to study the crystal structure stability of EuScCuSe₃ in the experimentally obtained Cmcm and the previously proposed Pnma space groups. It was shown that analysis of elastic properties as Raman and infrared spectroscopy are powerless for this particular task. The instability of EuScCuSe₃ in space group Pnma space group is shown on the basis of phonon dispersion curve simulation. The EuScCuSe₃ can be assigned to indirect wide-band gap semiconductors. It exhibits the properties of a soft ferromagnet at temperatures below 2 K.

Synthesis, structures and magnetic properties of the Eu-based quaternary tellurides EuGdCuTe3 and EuLuCuTe3

Novel paramagnetic tellurides EuGdCuTe3 and EuLuCuTe3, with the transition to a ferrimagnetic state at ∼8 K and ferromagnetic state at ∼3 K, respectively, are reported.

A Challenge toward Novel Quaternary Sulfides SrLnCuS3 (Ln = La, Nd, Tm): Unraveling Synthetic Pathways, Structures and Properties

We report on the novel heterometallic quaternary sulfides SrLnCuS₃ (Ln = La, Nd, Tm), obtained as both single crystals and powdered samples. The structures of both the single crystal and powdered samples of SrLaCuS₃ and SrNdCuS₃ belong to the orthorhombic space group Pnma but are of different structural types, while both samples of SrTmCuS₃ crystallize in the orthorhombic space group Cmcm with the structural type KZrCuS₃. Three-dimensional crystal structures of SrLaCuS₃ and SrNdCuS₃ are formed from the (Sr/Ln)S₇ capped trigonal prisms and CuS₄ tetrahedra. In SrLaCuS₃, alternating 2D layers are stacked, while the main backbone of the structure of SrNdCuS₃ is a polymeric 3D framework [(Sr/Ln)S₇]_n, strengthened by 1D polymeric chains (CuS₄)_n with 1D channels, filled by the other Sr²⁺/Ln³⁺ cations, which, in turn, form 1D dimeric ribbons. A 3D crystal structure of SrTmCuS₃ is constructed from the SrS₆ trigonal prisms, TmS₆ octahedra and CuS₄ tetrahedra. The latter two polyhedra are packed together into 2D layers, which are separated by 1D chains (SrS₆)_n and 1D free channels. In both crystal structures of SrLaCuS₃ obtained in this work, the crystallographic positions of strontium and lanthanum were partially mixed, while only in the structure of SrNdCuS₃, solved from the powder X-ray diffraction data, were the crystallographic positions of strontium and neodymium partially mixed. Band gaps of SrLnCuS₃ (Ln = La, Nd, Tm) were found to be 1.86, 1.94 and 2.57 eV, respectively. Both SrNdCuS₃ and SrTmCuS₃ were found to be paramagnetic at 20–300 K, with the experimental magnetic characteristics being in good agreement with the corresponding calculated parameters.