Low-Temperature Crystallization of Barium Ferrite Nanoparticles by a Sodium Citrate-Aided Synthetic Process

Abstract

This article describes the synthesis of barium ferrite nanoparticles at low crystallization temperatures using a sodium citrate-aided process. Monodispersed barium ferrite amorphous nanoparticles were synthesized by the formation of metal−citrate complexes at pH 10, followed by hydrolysis at 100 °C. The mean particle diameter was 4.7 nm with a specific surface area of 137.8 m2/g. This is the first time that sodium citrate has been used as a chelating agent in the synthesis of barium ferrite nanoparticles. Sodium citrate plays two important roles in the process: it allows the homogeneous mixing of two metal cations in the as-synthesized barium ferrite amorphous nanoparticles, and it retards particle growth via the formation of surface citrate complexes, inhibiting the agglomeration of the nanoparticles. The amorphous precursor nanoparticles were transformed into a hexagonal structure by calcination at elevated temperatures (500−750 °C) in air. XRD patterns showed that the amorphous phase of the nanoparticles was completely transformed to the hexagonal phase after calcination at 600 °C for 100 min, with no intermediate phase evident. This crystallization temperature was lower than previously reported crystallization temperatures. Crystallization behavior was examined using thermal analysis and FTIR measurements. Particle size, measured from SEM images, was increased from 35 to 130 nm by elevating the calcination temperature from 600 to 750 °C. Barium ferrite nanoparticles calcinated at 600 °C had high magnetic properties: the coercivity and saturation magnetization values were 3580 Oe and 43 emu/g, respectively.