A newly developed YbFeO3-YbCrO3-YbMnO3 pseudo-ternary phase diagram: Crystal structure, optical properties, and dielectric properties of seven selected orthorhombic ternary solid solution compounds

Abstract

We construct a YbFeO₃-YbCrO₃-YbMnO₃ pseudo-ternary phase diagram that illustrates the different equilibrium phases regions where orthorhombic, hexagonal, and orthorhombic, and hexagonal phases at room temperature coexist. Thirty-three Yb:Fe:Cr:Mn molar ratio compositions were designed using solid-state reactions. They were characterized by X-ray diffraction. Poor miscibility of the hexagonal single phase in a small region of the YbMnO₃-YbFeO₃ pseudo-binary phase was found. The maximum miscibility of Mn into the orthorhombic phase is found in the YbFe_0.50Cr_0.25Mn_0.25O₃, YbFe_0.375Cr_0.375Mn_0.25O₃, and YbFe_0.25Cr_0.50Mn_0.25O₃ intermediate ternary ceramic compound. Beyond this concentration of Mn, the YbFeO₃ - YbCrO₃ - YbMnO₃ pseudo-ternary system breaks down into mixing hexagonal and orthorhombic phases. Once the different phases were established; the crystalline structure, microstructure as well as optical and dielectric properties were investigated in seven selected compositions in the orthorhombic zone, where the total Fe – Cr and the partial Mn miscibility tunes the cell volume. SEM images reveal grains coalescence, indicating incipient fusion in the YbFeO₃ sample. As Cr and Mn increase, the sign of incipient fusion and grain size decreases. The dielectric properties were evaluated as a function of temperature, and through these quantities it is found that the electrical conductivity increases for the intermediate ceramic compound. This fact agrees with the optic band gap, E_g, which decreases for these intermediate compounds. According to the dielectric study, we found that the decrease in the E_g is mainly associated with charge carriers polarons (∼0.20–0.25 eV) at low-temperature and oxygen vacancies (0.55–0.61 eV) at high temperatures.