Impact of dysprosium doping on structural, dielectric and magnetic characteristics of bismuth based double perovskites

Dysprosium (Dy) doped BFCO [Bi2-xDyxFeCrO6 (x = 0.2, 0.4, and 0.6)] materials were synthesized using well-known solid state reaction method. From the X-ray diffraction technique, monoclinic structure was confirmed for all samples by employing Rietveld analysis. By using Williamson-Hall method, the strain and crystallite sizes were calculated. From the Fourier Transform Infra-red spectroscopy, metal oxide vibrations are confirmed. Room temperature (RT) Raman spectroscopy was used for identifying optical phonon modes as well as stretching-bending vibrations in the samples. The results from scanning electron microscopy study show that the average grain sizes of the Bi2-xDyxFeCrO6 (x = 0.2, 0.4, and 0.6) nanoparticles are 1.14, 0.87 and 0.70 mu m respectively. For optical characteristics, UV-Vis diffuse reflectance spectroscopy shows decrease in energy band gap with increasing Dy concentration. From the dielectric studies, Maxwell-Wagner model is seen with no hint of phase transition. There are two semicircles on the impedance diagram, signifying the existence of grain and grain-boundary effects. Activation energy values are found in between 0.5-1 eV and hence confirm that the doubly ionized oxygen vacancies (OVs) are accountable for the conduction process. AC conductivity (sigma ac) studies have been carried out and prove that it increases with rising temperature which is attributed to the hopping mechanism. Studies using P-E hysteresis loops demonstrate that when the concentration of Dy increases, remnant polarisation (Pr) also increases. Magnetic field measurements at RT (300 K) as well as at 5 and 100 K along with magnetization variation under zero field cooled (ZFC) and field cooled (FC) conditions were accomplished. With increase in the Dy concentration, the magnetization tends to increase at low temperatures.