Synthesis, Crystal Structure, and Optical and Magnetic Properties of the New Quaternary Erbium Telluride EuErCuTe[sub.3]: Experiment and Calculation

This paper reports for the first time on a new layered magnetic heterometallic erbium telluride EuErCuTe[sub.3]. Single crystals of the compound were obtained from the elements at 1120 K using CsI as a flux. The crystal structure of EuErCuTe[sub.3] 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 KZrCuS[sub.3] structure type. In the orthorhombic structure of erbium telluride, distorted octahedra ([ErTe[sub.6]][sup.9−]) form two-dimensional layers ({Er(Te1)2/2e(Te2)4/2k[sup.−]})∞2, while distorted tetrahedra ([CuTe[sub.4]][sup.7−]) form one-dimensionally connected substructures ({Cu(Te1)2/2e(Te2)2/1t[sup.5−]}∞1) along the [100] direction. The distorted octahedra and tetrahedra form parallel two-dimensional layers ({CuErTe3[sup.2−]}∞2) between which Eu[sup.2+] ions are located in a trigonal-prismatic coordination environment (EuTe6[sup.10−]). The trigonal prisms are connected by faces, forming chains ({Eu(Te1)2/2(Te2)4/2[sup.2−]}∞1) along the [100] direction. Regularities in the variations in structural parameters were established in the series of erbium chalcogenides (EuErCuCh [sub.3] with Ch = S, Se, and Te) and tellurides (EuLnCuTe[sub.3] with Ln = Gd, Er, and Lu). Ab-initio calculations of the crystal structure, phonon spectrum, and elastic properties of the compound EuErCuTe[sub.3] 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 EuErCuTe[sub.3] at temperatures below 4.2 K was ferrimagnetic, as were the sulfide and selenide derivatives (EuErCuCh [sub.3] 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.