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.

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) Å3. 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, crystal structures and spectroscopic properties of pure YSb2O4Br and YSb2O4Cl as well as Eu3+- and Tb3+-doped samples.

The quaternary halide-containing yttrium(iii) oxidoantimonates(iii) YSb2O4Cl and YSb2O4Br were synthesised through solid-state reactions from the binary components (Y2O3, Sb2O3 and YX3, X = Cl and Br) at 750 °C in evacuated fused silica ampoules with eutectic mixtures of NaX and CsX (X = Cl and Br) as fluxing agents. YSb2O4Cl crystallizes tetragonally in the non-centrosymmetric space group P4212 with unit-cell parameters of a = 773.56(4) pm and c = 878.91(6) pm, whereas YSb2O4Br is monoclinic (space group: P21/c) with a = 896.54(6) pm, b = 780.23(5) pm, c = 779.61(5) pm and ß = 91.398(3)°, both for Z = 4. The two new YSb2O4X compounds contain [YO8]13- polyhedra, which are connected via four common edges to form layers (d(Y3+-O2-) = 225-254 pm) without any Y3+⋯X- bonds (d(Y3+⋯X-) > 400 pm). Moreover, all oxygen atoms belong to ψ1-tetrahedral [SbO3]3- units, which are either connected to four-membered rings [Sb4O8]4- in the chloride (Y2[Sb4O8]Cl2 for Z = 2) or endless chains in the bromide (Y1/2(SbO2)Br1/2 for Z = 8) by common vertices. With distances of 307 pm in YSb2O4Cl and 326 pm in YSb2O4Br there are not even substantial bonding Sb3+⋯X- (X = Cl and Br) interactions at work. Luminescence spectroscopy on samples doped with trivalent europium and terbium showed an energy transfer from the oxidoantimonate(iii) moieties as the sensitizer in the host structure onto the lanthanoid activators.