Rietveld Refinement of Nanocrystalline LiFeO₂ Synthesized by Sol-Gel Method and Its Structural and Magnetic Properties

K. Vijaya Kumar, A. Sangeetha, A. T. Raghavender, Z. Skoko, G. Nanda Kumar

Department of Physics, Faculty of Science, University of Zagreb, Bijenicka c., Zagreb, Croatia.
Department of Physics, Indur Institute of Engineering and Technology, Siddipet.
Department of Physics, Jawaharlal Nehru Technological University Hyderabad, College of Engineering, A.P., India.
Dept of Geo-Physics, Osmania University, Hyderabad, A. P., India.
Nanomagnetism Lab, Department of Physics and Astronomy, Seoul National University, Seoul, South Korea.

DOI: 10.4236/jcpt.2012.24022                

Abstract

Nanocrystalline lithium iron oxide LiFeO₂ was synthesized using sol-gel method. Rietveld analysis was performed to confirm the different phases associated in the formation of LiFeO₂. Quantitative Rietveld refinement revealed that sample contains: 39.9 wt% of cubic α – LiFeO₂ phase, 58.5 wt% of monoclinic β - LiFeO₂ and tetragonal 1.7 wt%. of γ - LiFeO₂. The nanocrystalline nature of the prepared samples was confirmed by SEM analysis. The magnetic properties of LiFeO₂ showed ferromagnetic property at room temperature.

Keywords

Nanoparticles; LiFeO₂; Structural and Magnetic Properties

1. Introduction

Lithium iron oxide was found to be the most promising and very interesting materials due to their potential applications as a cathode for rechargeable lithium batteries and also due to low cost and toxicity [1-3]. Lithium iron oxide LiFeO₂ has NaCl type cubic closed packed (ccp) crystal structure with Li⁺ and Fe³⁺ being distributed in octahedral sites. LiFeO₂ crystallizes in different polymorphic modifications (α, β, γ) based on the synthesis techniques and preparation conditions [4-6]. The unit cell of α-LiFeO₂ has cubic distorted form with space group Fm3m. In α-LiFeO₂ structure, Li⁺ and Fe³⁺ ions occupy randomly the octahedral sites [7]. γ-LiFeO₂ structure is tetragonal cation disordered. Li⁺ and Fe³⁺ in the octahedral sites transform from cubic structure (Fm3m) to tetragonal (I4/m) structure [8]. In the case of monoclinic β-LiFeO₂ the cation ordering was detected [5,8]. It was observed that synthesis of LiFeO₂ is a difficult task as several phases are associated during preparation process. Earlier LiFeO₂ have been synthesized by different techniques such as hydrothermal [6,9], citrate precursor method [10], solid state reaction [11], ion exchange reaction [12] etc. and observed different polymorphic phases and improved structural and electrical properties. In this paper we made an attempt to synthesize nanocrystalline LiFeO₂ using sol-gel method. To clearly understand the structural formation and the corresponding phases of LiFeO₂ and the underlying magnetic properties we have carried the present work.

2. Experimental

The LiFeO₂ nanoparticles have been synthesized by sol-gel method [13]. The AR grade citric acid (C₆H₈O₇·H₂O), ferric nitrate (Fe(NO₃)₃·9H₂O) and lithium nitrate (LiNO₃) (≥99%) were used as starting materials. The entire synthesis procedure is described elsewhere [13]. The as prepared powder samples were sintered at 500˚C for 5 h.

Crystallographic structure of LiFeO₂ nanopowder was measured using Philips PW 3020 Bragg-Brentano diffractometer using Cu Kα radiation (wave length λ = 1.54 Å). The morphology of powder was observed using scanning electron microscopy (SEM) from Carl Zeiss. Room temperature magnetization was measured using ADE magnetics DMS 4 Vibrating Sample Magnetometer (VSM).

3. Results and Discussions

Figure 1 shows (a) experimental and (b) calculated X-ray diffraction patterns of nanocrystalline LiFeO₂. Crystal structures of different phases present in the

Conflicts of Interest

The authors declare no conflicts of interest.

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