Erbium Doped Cobalt Nano-Ferrites : Preparation and structural Properties

Edapalli Sumalatha, D. Ravinder,N.V.Krishna Prasad2, Khalid Mujasam Batoo, Emad H. Raslan and Muhammad Hadi Department of Physics, Osmania University, Hyderabad-500007, Telangana, India 3Department of Physics, GITAM Deemed to be University, Bangalore, Karnataka-562163, India King Abdullah Institute for Nanotechnology, King Saud University, P.O. Box-2455, Riyadh11451, Saudi Arabia. Department of Physics, College of Science,King Saud University, P.O. Box-2455, Riyadh-11451, Saudi Arabia. *Corresponding Author Email ID: ravindergupta28@rediffmail.com Abstract: Synthesized nano-ferrits of Cobalt-Erbium having chemical formula CoErxFe2-xO4(x= 0 to 0.030 with step size 0.05) were characterized using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Structural variables that include lattice constant (a), crystallite size (D), X-ray density (dx) and surface area (s) were computed from XRD patterns. XRD patterns confirmed single phase cubic spinal structure while TEM results revealed homogeneous nature of particles accompanied by clusters without impurity peaks. The observed results are explained on the basis of composition.

moderate dielectric constant, high initial permeability and saturation magnetization. Doping and thermal changes during synthesis and processing of cobalt-ferrites alter the distribution of metal ions influencing their structure and magnetic properties [6]. It is reported that the net magnetic moment of lanthanide series elements/ions depend on f-orbital electron number in which Er +3 is of small size (89 pm) with large magnetic moment (7 μB) [7]. Low eddy current and high resistivity makes ferrites better choice than metals [8]. The present work reports the preparation and characterization of erbium doped cobalt ferrites using Citrate-gel auto combustion.

Synthesis of Cobalt-Erbium nano-ferrites with citrate-gel auto combustion technique
Cobalt Nitrate (Co(NO3)2·6H2O), Ferric Nitrate (Fe(NO3)3·9H2O), Erbium Nitrate (Er (NO3).6H2O), Citric Acid (C6H8O7·H2O) and Ammonia solution (NH3) of 99.9% purity weighed as per stoichiometric ratio were used as starting materials. Liquefaction of metal nitrates in distilled water was done and the mixture was stirred at 300 rpm for one hour to obtain a clear homogeneous solution. Next citric acid in aqueous form and metal nitrate was maintained in 1:3 ratio for all samples. Now, ammonia solution was added drop by drop to maintain Ph=7. This solution on stirring was heated at 100 °C temperature for ten to twelve hours to form a viscous gel. The water contained in the mixture gets evaporated slowly to form dry gel generating internal combustion to form a black colored sample. This sample was manually grinded and calcinated at 500°C for four hours. Later these samples in pellet or powder form are characterized with XRD ( Bruker, CuKα,λ = 0.15406nm) and TEM ( Model JEOL2100F,Japan). Figure.1 depicts the XRD pattern of Co-Er nano-ferrites which indicated single-phase cubic spinel structure without any impurity peak. Figure. where 'λ' = wavelength of X-ray,'β'= peak width at half maximum height and constant 'K'=0.9.

XRD Analysis of Co-Er nano-ferrites:
The data related to intense peak (311) was used in estimating the size (L). The results indicated reduction in size of crystallite from 20.84 nmto14.40 nm ( x=0.0 to 0.030). The values of lattice parameter, crystal size, X-ray density and surface area has been displayed in Table.1. It can be seen from the table that lattice parameter increases with increase in erbium content. This increase is due to replacement of eight small Co 2+ and Fe 3+ ions with big Er 3+ ions. Huge difference in radii of these three ions induce strain during lattice formation and diffusion processes.
Requirement of more energy in absorbing RE 3+ ions with more radii while replacing Fe 3+ to form RE-O bond decreases crystallization energy leading to particles of small size. Earlier reports indicated similar results on RE-ion substituted cobalt ferrites [15][16][17][18][19][20]. Therefore, XRD results are liable for expansion of unit cell due to larger Er 3+ ion doping in CFO. Calculation of X-ray density (Dx) was done using the equation [21] dx = 8 *
X-ray density is found to increase from 5.3344gm/cm 3 to 5.3392gm/cm 3 (x = 0.00 to x =0.030) with increasing Er 3+ content. Cobalt ferrite in inverse spinel form has tetrahedral site half occupied by Fe +3 and octahedral sites occupied by remaining half of Fe +3 and Co -2 ions [22,23].
Any change in site occupation by Fe +3 and Co -2 ions might be due to preparation technique and affect cell constant. Here, S= area of surface, D= crystallite size, d=Bulk density

TEM Analysis:
Phase structure and morphology studies of the synthesized samples were taken up by using TEM analysis. Figure3. shows the TEM images and their respective SAED images with particle size distribution chart for all samples respectively. TEM and SAED images demonstrated spherical shape and low thickness for majority of the nanoparticles along with few elongated particles.
TEM images confirmed well distanced particles for lower concentration of Er +3 ions and increase in Er +3 ion substitution leads to agglomeration of particles due to magnetic nano-particle interaction. TEM images indicated the particle size ranging between 16nm-24nm.

Conclusions:
Erbium substituted Co-Er nano-ferrites were synthesized and characterized. Significant induced effect of Erbium was observed on crystal structure and morphology. Crystal size decreased with increased Erbium content. Study of CoErxFe2-xO4 for compositions with cobalt content (x=0.0 to 0.030) indicated decrease in crystallite size with increasing erbium content and increased particle surface area making it suitable for a good adsorbent. Hence these adsorbents can be used