Physical properties and dielectric response of (Gd, Pr)-dual doped samarium iron garnet

Abstract

Samarium iron garnet, Sm3Fe5O12, co-doped with Gd3+ and Pr3+ ions, having the chemical formula Sm3-2xGdxPrxFe5O12 (0.0 ≤ x ≤ 0.8), were synthesized by the co-precipitation method. The structural study confirmed the cubic crystallization of the Sm3Fe5O12 phase in the addition of two secondary phases, α-Fe2O3 and SmFeO3. The variation of the lattice parameters and crystalline size indicated that both Gd3+ and Pr3+ ions were incorporated into the lattice. The elemental analysis confirmed the stoichiometry proposed for Sm3-2xGdxPrxFe5O12. The co-doping process of SmIG affected the absorbance of photo-radiations, making them possible candidates for transparent electrodes and optoelectronic devices. Energy band gap values were in the range of 2.921–3.004eV. DC electrical conductivity measurements studied the transport properties through which two activation energies were determined. The co-doping process affected the dielectric constants (ε′, ε″, tan δ), which reached a maximum value for x = 0.2. Dielectric relaxation was observed in the measurements, which could be due to the presence of oxygen vacancies as detected in XPS results. The Nyquist plots revealed that all the samples exhibited a negative temperature coefficient of impedance, where the arc of the semicircles decreased as the temperature increased from 413 to 743K. Also, the contribution of the resistance at high-frequency was related to the grains and grain boundaries. The ac conductivity mechanism followed the small polaron and the correlated barrier hopping models. In the temperature range between 333 and 583K, the prepared samples are promising for ion-conducting glasses and ionic crystals.