Structural characterization, dielectric, and magnetic properties of Ti-doped YFeO3 multiferroic compound

Crystal structure, and magnetic and dielectric properties were studied in Ti-doped YFeO₃ polycrystalline samples. The crystal structure and chemical state of the Fe/Ti cations were characterized by a combination of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It is found that a narrow solid-solubility limit is achieved (~ 6%) and the d⁰–ness of Ti⁴⁺ is not favored in the YFeO₃ matrix. A change in the valence states of Fe and Ti cations explains not only the low solubility limit but also the anomalous increase of the volume cell. Soft magnetic hysteresis curves in the M vs H curves indicate that the weak ferromagnetic contribution prevails for all the studied samples. Furthermore, by means of differential calorimetry (DSC) it was possible to identify the AFM transition which decreases with increasing Ti content. On the other hand, the change of the step-like anomaly to a broad peak in the permittivity (ε′) and loss tangent (tan δ) as Ti content increases resemble to a relaxor ferroelectric transition. The endothermic peak (DSC) around the magnetic transition and the broad peaks in the ε′(T) data seem to indicate the existence of a local polarization coupled with AFM transition at ~ 650 K. Two types of charge carriers were found in the doped systems, oxygen vacancies at high temperatures, and small polarons at low temperatures, respectively. Besides, it is found that the introduction of those charge carriers in the YFeO₃ matrix occurs by the change of oxidation state from Fe³⁺ to Fe²⁺ through Ti³⁺.