Effect of trivalent transition metal ion substitution in multifunctional properties of Dy_2O_3 system

摘要

The present work describes the systematic study on inducing multiferroic properties in non-magnetic Dy_2O_3 system. The ceramic compounds of Dy_(2-x)Fe_xO_3 (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 Dy_2O_3 crystal structure. By Rietveld analysis, it is determined that with respect to increasing concentration of Fe~(3+) ion at Dy~(3+) site leads to transformation of crystal structure from Cubic to Orthorhombic with varying concentration of DyFeO_3 phase and further increase in Fe~(3+) concentration leads to the formation of Garnet phase in Dy_(2-x)Fe_xO_3 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 Dy_2O_3 system which may effects on the electrical transport properties of the materials and increasing concentration of Fe in Dy_2O_3 system is also analyzed by energy dispersive analysis spectra. By Raman spectral analysis, it is identified that the strong absorption band of Cubic Dy_2O_3 compound at 373 cm~(-1) is gradually shifted to 257 cm~(-1) which indicates the molecular stretching motion of RE-O bond in REO_6 octahedra and the large deviation in position of intense Raman bands below 300 cm~(-1) confirms the incorporation of Fe~(3+) ion in the host Dy_2O_3 lattice and imparting large polarizability in the prepared compounds due to translational motions of ReO_6 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 DyFeO_3 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-x)Fe_xO_3 system, the compounds exhibits paramagnetic nature whereas from x=1.0 i.e. DyFeO_3, 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 Fe~(3+) ion in Dy~(3+) 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_(0.6)Fe_(1.4)O_3 compound is 0.2 μC/cm~2 and found comparable with the results observed from Bismuth Ferrite related compounds.