Journal of Electromagnetic Analysis and Applications
Vol. 2  No. 1 (2010) , Article ID: 1234 , 5 pages DOI:10.4236/jemaa.2010.21008

Cation Distribution in Lithium Ferrite (LiFe5O8) Prepared via Aerosol Route

Sonal Singhal1,*, Kailash Chandra2


1Department of Chemistry, Panjab University, Chandigarh, India; 2Institute Instrumentation Centre, Indian Institute of Technology, Roorkee, India.


Received July 16th, 2009; revised August 22nd, 2009; accepted September 7th, 2009.

Keywords: Nano Particles, Saturation Magnetization, Coercivity, X-Ray Diffraction, Mössbauer Spectra


Nano size lithium ferrite was prepared through aerosol route and characterized using TEM, XRD, magnetic measurements and Mössbauer spectroscopy. The particle size of as obtained samples were found to be ~10 nm through TEM, that increases upto ~80 nm on annealing at 1200 oC. The unit cell parameter ‘a’ calculated using XRD, confirms the formation of a-LiFe5O8. Room temperature Mössbauer spectra of as obtained sample of all the ferrites exhibited broad doublet suggesting super paramagnetic nature. This doublet further resolved into two doublets and assigned to the surface region atoms and internal region atoms of the particles. The annealed samples (1200 oC) show broad sextets, which were fitted with two sextets indicating different local environment of both tetrahedrally and octahedrally coordinated Fe-cation. Cation distribution obtained from the X-ray, magnetic and Mössbauer data confirms that the three fifth of the iron atom goes in to the octahedral site.

1. Introduction

Lithium iron oxides LiFe5O8 are of increasing scientific interest and are also promising candidates for cathode materials in rechargeable lithium batteries [1,2]. Its high curie temperature, high saturation magnetization and hysterisis loop properties after performance advantages over other spinel ferrites used in microwave frequency and magnetic core applications [1–4]. Two separate crystallographic ordered and disordered forms of LiFe5O8 ­have been isolated. A super structured form in which lithium and iron atoms are ordered is called aLiFe5O8 and has a subgroup of Fd-3m with a primitive cubic unit cell (space group P433 or P413, a = 8.3372 Å) [5]. They are based on the inverse spinel structure with lithium and three fifth of the total Fe3+ occupying octahedral sites [6]. However, disordered form of lithium ferrites has a random statistical distribution of lithium and iron over all the octahedral positions [7]. Various preparation methods have been developed such as double sintering ceramic techniques, hydrothermal precipitate, hydrothermal ball milling and so on [8,9]. The high temperature used in all these techniques lower the magnetization due to the precipitation of a-Fe2O3 or the formation of Fe3O4 [10].

The present work deals with the synthesis of nano particles of lithium ferrite via aerosol route at a temperature ~600 oC. This avoids the precipitation of a-Fe2O3 or Fe3O4. On the other hand in aerosol method particle size, degree of agglomeration, chemical homogeneity can be controlled with relative ease. Aerosol method has the potential of producing multicomponent materials and production of powder by this method is commercially viable [10,11].

The sample so prepared was characterized using transmission electron microscope (TEM), X-ray diffractometer (XRD), magnetic and Mössbauer spectrometer. This work is an attempt to investigate the cation distribution using XRD, magnetic and Mössbauer measurements.

2. Experimental

Nano particles of lithium ferrite (LiFe5O8) were prepared via aerosol route using a setup described in our earlier papers [12–14]. The desired proportions of lithium and iron nitrates were weighed and dissolved in water to prepare 5 x 10-2 M solutions. Air pressure, sample uptake and furnace temperature were maintained at 40 psi, 3-4 ml/min and ~600 oC respectively during preparation. The ferrite powder was deposited on the teflon coated pan.

The elemental analysis was carried out on an electron probe micro analyzer (EPMA) (JEOL, 8600 M) and atomic absorption spectrophotometer (AAS) (GBC, Avanta),

Figure 1. X-ray diffractographs of LiFe5O8 after annealing at various temperatures

while the particle morphology was examined by transmission electron microscope (TEM) (Philips, EM400). The X-ray diffraction (XRD) studies were carried on Xray spectrometer (Bruker AXS, D8 Advance) with FeKa radiation and magnetic measurements were made on a vibrating sample magnetometer (VSM) (155, PAR). Mössbauer spectra were recorded on a constant acceleration transducer driven Mössbauer spectrometer using 57Co(Rh) source of 25 mCi initial activity. The spectrometer was calibrated using a natural iron foil as well as recrystallized sodium nitroprusside dihydrate (SNP) as standards.

3. Results and Discussion

Elemental analytical data for Li and Fe were obtained by EPMA. About 2 mm thick pellet was prepared, fixed on the sample holder and coated with the carbon to make them conducting. Elemental analysis was carried out at eight different points on each pellet with spot size of ~10 mm dia and results were found to be consistent. The results were further verified by atomic absorption spectrophotometer.

3.1 Transmission Electron Microscope

The TEM micrograph of a very small amount of as obtained samples placed on the carbon grid shows spherical particles of ~100-300 nm size as reported in our earlier papers [13,14]. However, after agitating ultrasonically and taking the suspended particles on the carbon grid shows well separated particles of size ~10 nm. The micrographs for sample annealed at 1200 oC shows that the particle size increases with annealing temperature. It is widely believed that the net decrease in free energy of solid-solid and solid-vapour interface provides the necessary driving force for particle growth during annealing process [15].

3.2 X-Ray Diffractographs

The powder X-ray diffractographs of as obtained sample and that of annealed at various temperatures is given in Figure 1. The diffraction pattern of as obtained samples confirms the amorphous nature of the samples. Peaks start appearing and the lines become sharper as the annealing temperature increases due to the grain growth at higher temperatures. The crystallite size was calculated from the most intense peak (311) using Sherrer equation [16]. It is seen that the particle size increases upto ~80 nm as the annealing temperatures are raised to 1200 oC. The lattice parameters were calculated using Powley as well as Le Bail refinement methods (built in TOPAS V2.1 of BRUKER AXS) and found to be a = b = c = 8.33103 Å and V = 578.22 Å3. The data confirm the presence of a-LiFe5O8 formation. Rietvald analysis of the annealed sample further confirms a single phase cubic spinel structure, a-LiFe5O8, as given in Figure 2.

X-ray diffraction intensity calculations were carried out using the formula suggested by Buerger [17]

Ihkl = │Fhkl2PLp

where, notations have their usual meanings. It is well known that, the intensity ratio of planes I(220)/I(400), I(220)/I(440) and I(400)/I(440) are considered to be sensitive to the cation distribution, therefore, these ratios were used in estimating cation distribution. Finally, the cation distribution is estimated from X-ray intensity calculations for the best fit cation distribution and found to be [Fe2]A[LiFe3]BO8.

3.3 Magnetic Measurements

Magnetic hysteresis loops, at room temperature were recorded for the as obtained as well as annealed sample. Typical loops for as obtained LiFe5O8 and after annealing at 1200 oC are shown in Figure 3. The as obtained sam-

Figure 2. Rietvald analysis of LiFe5O8 after annealing the sample at 1200 0C

Figure 3. Hysterisis loop of lithium ferrite sample (a) as obtained and (b) after annealing at 1200

ple exhibits no hysteresis, which may be attributed to superparamagnetic relaxation as confirmed by XRD. The values of saturation magnetization and magnetron nB (the saturation magnetization per formula unit in Bohr magnetron) at 300 K for the annealed sample were obtained from the hysterisis loop and found to be 66.92 emu/g and 4.99 respectively. According to Neel’s two sublattice model of ferrimagnetism, the magnetic moment per formula unit (mB), nBN(x) is expressed as:

nBN(x) = MB(x) – MA(x)

where MB and MA are the Band Asublattice magnetic moment in mB respectively. The nBN(x) value was calculated using the ionic magnetic moments of Fe3+ and Li+ which are 5 mB and 0 mB respectively. The calculated value (5 mB) clearly indicates the inverse spinel structure with lithium and three fifth of the total Fe3+ occupying octahedral sites and two fifth occupying tetrahedral site.

3.4 Mössbauer Spectra

Figure 4 shows the typical Mössbauer spectra of LiFe5O8 at room temperature for the as obtained sample. The presence of broad doublet in this figure indicates the superparamagnetic nature of the sample. Since in the small particles (<10 nm) a substantial fraction of atoms resides on the surface, a different environment is experienced by them as compared to those inside the particle. Therefore, this broad doublet was fitted with two sets of doublets, one for atoms in the surface region (d = 0.45 mms-1 and DEQ = 1.02 mms-1) and the other for those in the internal region (d = 0.45 mms-1 and DEQ = 0.60 mms-1) of the particles. Larger quadrupole splitting due to surface region atoms compared to internal region atoms can be attributed to the existence of a broader distribution of interatomic spacing and partly disordering in the surface region of the ultrafine particles. It is clear that the contri-

Figure 4. Mössbauer spectra of lithium ferrite (a) as obtained and (b) after annealing at 1200 0C

bution of surface region atoms is 42 % of total area of the experiment spectrum. This is in agreement with the percentage (44 %) of the volume of surface region atoms to the total volume of the particle with an average grain size (8 nm) by Ma et al. [18].

The Mössbauer spectra recorded at 300 K after annealing at 1200 oC (Figure 4b) exhibit two normal zeeman split sextets due to the A-site Fe3+ ions and other due to B-site Fe3+ having hyperfine fields 500 and 484 kOe respectively, which indicates ferrimagnetic behaviour of the sample. The cation distribution was also calculated using the intensity ratio of the sextets corresponding to the tetrahedral and octahedral sites. The intensity ratio was found to be 2 : 3 which further confirms that the three fifth iron atoms goes in to octahedral site. The cation distribution obtained from the X-ray intensity data and magnetic moment data agrees fairly well with the cation distribution estimated from Mössbauer data.

4. Conclusions

Lithium ferrite has been prepared successfully with particle size ~10 nm by aerosol route with high yield. After annealing the sample at 1200 oC confirms the formation of single phase a-LiFe5O8. The cation distribution obtained from the X-ray, magnetic and Mössbauer data confirms that the three fifth of the iron atom goes in to the octahedral site.

Since Lithium ferrite and mixed lithium ferrites have very high potential for cathode materials in rechargeable lithium batteries, microwave applications and, especially as replacements for garnets, due to their low cost. The squareness of the hysteresis loop and superior temperature performance are other prominent advantages that have made them very promising candidates for application in microwave devices. In this communication we report our studies on the synthesis of lithium ferrite and their magnetic properties and the work is going on with the mixed lithium ferrites to improve their magnetic properties and their applications in different fields.


  1. P. D. Baba and G. M. Argentina, “Microwave lithium ferrites: An overview,” IEEE Transactions Microwave Theory and Techniques, Vol. 22, pp. 652–658, June 1974.
  2. H. M. Widatallah, C. Johnson, F. J. Berry, and M. Pekala, “Synthesis, structural, and magnetic characterisation of magnesium-doped lithium ferrite of composition Li0.5Fe2.5 O4,” Solid State Communications, Vol. 120, pp. 171–175, October 2001.
  3. V. Berbenni, A. Mariniand, and D. Capsoni, “Solid state reaction study of the system Li2CO3/Fe2O3,” Z. Naturforsch, Vol. 53(a), pp. 997–1003, November 1998.
  4. J. S. Baijal, S. Pehanjoubam and D. Kothari, “Hyperfine interactions and magnetic studies of Li-Mg ferrites,” Solid State Communications, Vol. 83, pp. 679–681, September 1992.
  5. H. M. Widatallah and F. J. Berry, “The influence of mechanical milling and subsequent calcination on the formation of lithium ferrites,” Journal of Solid State Chemistry, Vol. 164, pp. 230–236, March 2002.
  6. N. K. Gill and R. K. Puri, “D.C. resistivity of Cr3+ substituted lithium ferrites,” Journal of Materials Science Letters, Vol. 4, pp. 396–398, April 1985.
  7. H. Yang, Z. Wang, M. Zhao, J. Wang, D. Han. H. Luo, and L. Wang, “A study of the magnetic properties of nanocrystalline LiFe5O8 and Li0.5Fe2.3Cr0.2O4 particles,” Materials Chemistry and Physics, Vol. 48, pp. 60–63, March 1997.
  8. A. Ahniyaz, T. Fujwara, S. Song, and M. Yoshimura, “Low temperature preparation of β-LiFe5O8 fine particles by hydrothermal ball milling,” Solid State Ionics, Vol. 151, pp. 419–423, November 2002.
  9. R. Laishram, C. Prakash, S. Phanjoubam, and H. N. K. Sarma, “Mössbauer effect studies on lithium ferrite substituted with chromium and antimony,” Modern Physics Letters, Vol. B17, pp. 67–73, January 2003.
  10. E. J. Cukauskas, L. H. Allen, H. S. Newman, R. L. Henry, and P. K. Van Damme, “The properties of Y1Ba2Cu3O7−δ thin films with silver doping prepared by spray pyrolysis,” Journal of Applied Physics, Vol. 67, pp. 6946–6952, June 1990.
  11. M. J. Hampden-Smith and T. T. Kodas,” Chemical aspects of aerosol synthesis of inorganic materials,” Journal of Aerosol Science, Vol. 26, S547–S548, September 1995.
  12. S. Singhal, A. N. Garg and K. Chandra, “Evolution of the magnetic properties during the thermal treatment of nanosize BaMFe11O19 (M=Fe, Co, Ni and Al) obtained through aerosol route,” Journal of Magnetism and Magnetic Materials, Vol. 285, pp. 193–198, January 2005.
  13. S. Singhal, S. K. Barthwal, and K. Chandra, “Preparation and characterization of nanosize nickel-substituted cobalt ferrites (Co1−xNixFe2O4),” Journal of Solid State Chemistry, Vol. 178, pp. 3183–3189, October 2005.
  14. S. Singhal, S. K. Barthwal, and K. Chandra,” Structural, magnetic and Mössbauer spectral studies of nanosize aluminum substituted Nickel-zinc ferrites,” Journal of Magnetism and Magnetic Materials, Vol. 296, pp. 94–103, January 2006.
  15. A. C. F. Costa, E. Tortella, M. R. Morelli, E. F. Neto, and R. H. G. A. Kiminami, “Sintering of Ni-Zn ferrite nanopowders by the constant heating rate (CHR) method, Materials Research,” Vol. 7, pp. 523–528, December 2004.
  16. H. P. Klug and L. E. Alexander, “X-ray diffraction procedures for poly crystalline and amorphous materials,” Second Edition, Wiley, 1974.
  17. M. G. Buerger, “Crystal structure analysis,” Wiley Interscience, New York, 1960.
  18. Y. G. Ma, M. Z. Jin, M. L. Liu, G. Chen, Y. Sui, Y. Tian, G. J. Zhang, and Y. Q. Jia, “Effect of high pressure on Mössbauer spectra of NiFe2O4 ultrafine particles with different grain sizes, ” Materials Chemistry and Physics, Vol. 65, pp. 79–84, June 2000.