Phase Relations in the Tl2Te-TlBiTe2-TlGdTe2 Compositions Region of the Tl-Bi-Gd-Te System and Magnetic Properties of the TlBi1−xGdxTe2 Solid Solutions

Abstract

Heavy p-elements-rare earth element tellurides are important multifunctional materials with thermoelectric, magnetic, optical, topological insulating, and other properties. This paper presents the results of a study of phase equilibria in the Tl₂Te-TlBiTe₂-TlGdTe₂ system and the magnetic properties of the TlBi_1−xGd_xTe₂ solid solutions. A diagram of solid-phase equilibria of the indicated system has been constructed. According to the data obtained, it is characterized by the formation of wide areas of homogeneity based on the initial compounds of the TlBiTe₂-TlGdTe₂ boundary system and a continuous series of solid solutions along the Tl₉BiTe₆-Tl₉GdTe₆ section (δ-phase). It has been shown that the homogeneity regions of the TlBiTe₂ (β₁) and TlGdTe₂ (β₂) compounds form a narrow (1-2 mol.%) band extending to 35 and 10 mol.% TlGdTe₂ and TlBiTe₂, respectively, along the boundary TlBiTe₂-TlGdTe₂ system while the homogeneity area of the δ-phase significantly extends into the compositions region rich in Tl₂Te. Based on powder diffraction patterns, the phase compositions of the alloys and the crystallographic parameters of the identified solid solutions were determined. The work also presents several polythermal sections, isothermal sections at 760 and 800 K of the phase diagram, as well as a projection of the liquidus and solidus surface of the Tl₂Te-Tl₉BiTe₆-Tl₉GdTe₆ subsystem. Magnetic properties of TlBi_1−xGd_xTe₂ samples were investigated by magnetization and Electron Paramagnetic Resonance (EPR) measurements. It was found that these samples behave as a Curie-Weiss paramagnet containing Gd³⁺ ions with no indications of magnetic ordering or freezing down to 2 K.