Effect of trivalent transition metal ion substitution in multifunctional properties of Dy₂O₃ system

Abstract

The present work describes the systematic study on inducing multiferroic properties in non-magnetic Dy₂O₃ system. The ceramic compounds of Dy_2−xFe_xO₃ (where x = 0.1–1.5) have been prepared by solid state reaction method. The powder X-ray diffraction patterns of all the prepared compounds reveal the strong influence of transition metal ion (Fe) in the Dy₂O₃ crystal structure. By Rietveld analysis, it is determined that with respect to increasing concentration of Fe³⁺ ion at Dy³⁺ site leads to transformation of crystal structure from Cubic to Orthorhombic with varying concentration of DyFeO₃ phase and further increase in Fe³⁺ concentration leads to the formation of Garnet phase in Dy_2−xFe_xO₃ compounds. The scanning electron microscopic images of the samples confirm the change in surface morphology with increasing grain boundaries and porosity due to the substitution of Fe in Dy₂O₃ system which may effects on the electrical transport properties of the materials and increasing concentration of Fe in Dy₂O₃ system is also analyzed by energy dispersive analysis spectra. By Raman spectral analysis, it is identified that the strong absorption band of Cubic Dy₂O₃ compound at 373 cm⁻¹ is gradually shifted to 257 cm⁻¹ which indicates the molecular stretching motion of RE–O bond in REO₆ octahedra and the large deviation in position of intense Raman bands below 300 cm⁻¹ confirms the incorporation of Fe³⁺ ion in the host Dy₂O₃ lattice and imparting large polarizability in the prepared compounds due to translational motions of ReO₆ octahedrons by variation in bond length and reduced mass of the bonding atoms. Diffused reflectance spectroscopy analysis implies the semiconducting nature of all the prepared compounds. It is also identified that the energy gap values goes on decreasing till DyFeO₃ and then starts increasing due to change in crystal structure by cubic to orthorhombic and then orthorhombic to garnet phase. From the magnetization studies, it is found that till even substitution of Fe (i.e. x = 0.1–0.9) in Dy_2−xFe_xO₃ system, the compounds exhibits paramagnetic nature whereas from x = 1.0 i.e. DyFeO₃, the samples exhibits ferromagnetic nature. The variation of magnetization behaviour from paramagnetic to ferromagnetic in higher concentration of Fe explicit the feasibility of attaining ferroic behaviour in Garnet mixed phase ceramic compounds. The electric polarization analysis reveal that while substituting Fe³⁺ ion in Dy³⁺ site by more than 50% of molecular ratio, the compounds exhibits non-zero remanance and coercivity values with respect to applied d.c. electric field and evident peculiar ferroelectric characteristic of those compounds. The maximum saturation polarization achieved in Dy_0.6Fe_1.4O₃ compound is 0.2 µC/cm² and found comparable with the results observed from Bismuth Ferrite related compounds.