Electron Paramagnetic Resonance (EPR) Investigations of Iron-Doped Ferroelectric Ternary Thallium Chalcogenides

In this review article, we summarize the results of the first investigations of EPR spectra of iron-doped ternary thallium chalcogenides TlInS2, TlGaSe2, and TlGaS2 in a wide temperature interval including previously reported structural phase transitions. In these compounds, Fe ions substituted Ga and/or In sites in crystal structure and served as local probes to study ligand crystal field and its local symmetry around these paramagnetic sites. An overview of our recent EPR studies carried out at room temperature and in the temperature interval including structural phase transitions is provided. The results revealed the fine structure of EPR spectra of the paramagnetic Fe3 + ions and the local symmetry of crystal field (CF) at Fe3 + site and CF parameters. As a result of summarizing the low-temperature EPR investigations a discussion about active atomic groups, possible atomic displacements, and the local symmetry changes during the low-temperature phase transformations is presented.