Synthesis and magnetic properties of chromium‑based cu(cr‑ti)s thiospinels and their deficient structures cu‑cr ti s obtained by copper extraction

Abstract

The crystalline structure of spinels is extremely flexible due to the presence of several sublattices in which the cations can be distributed and localized in different crystallographic sites depending on their sizes, oxidation states or coordination numbers. Cationic substitution and ions-extraction are appropriate tools to change the oxidation state inside the spinel structure, thus substantially modifying the magnetic properties. The spinel sulfide CuCr2S4 is a metallic ferromagnet with TC = 377 K, where Cr is mixed-valence Cr3+/Cr4+, while CuTi2S4 is a Pauli paramagnet, with Ti in a mixed-valence state (singlet ground state for Ti3+ ; nonmagnetic, S = 0, state for Ti4+). The copper ion Cu+ is in a closed-shell configuration. The mixed spinel CuCr2‑xTixS4 gives the possibility to change the oxidation state of Cr ions when titanium ions are introduced. Another way to control the oxidation state of the ions is by copper extraction from the lattice, thus producing a change in the magnetic behavior of the material. We report the synthesis, crystallographic and magnetic properties of the solid solution CuCr2‑xTixS4 and its deficient‑spinel structure obtained by copper extraction. Powder samples of CuCr2‑xTixS4 were prepared in quartz ampoules at 900 °C. Deficient spinels Cu1‑yoyCr2‑xTixS4 were prepared by mild treatment with oxidizing agents such as iodine in acetonitrile at 50 °C.