Study on The Influence of Crystal Structure and Grain Size on Dielectric Properties of Manganese Ferrite (MnFe2O4) Nanoparticles

Manganese ferrite (MnFe2O4) has been successfully synthesized by using coprecipitation methods with a various particles size of 13.1, 13.8, 16.2, 18.1, and 18.4 nm. Analysis of crystal structure properties which has been carried out by using XRD (X-Ray Diffraction) method revealed that all samples belong to cubic spinel structure. The measurement used computerized impedance spectroscopy system in the frequency range of 10120 Hz. The real dielectric constant (εʹ), imaginary dielectric constant (ε”), and impedance (Z) were determined at room temperature as a function of frequency. The dielectric constant (real and imaginary) and impedance decreased with frequency up to 70 kHz, and then it was constant at a frequency more than 70 kHz. The dielectric properties depending on the crystal structure are also investigated, it consists of the degree of crystallinity, lattice parameter, strain, X-ray density and the impurities of the sample. In the range of grain size of 13.1-18.4 nm, the real (εʹ) and imaginary (ε”) dielectric constants, and loss tangent increased with the increase of the grain size. In addition, impedance (Z) decreased with increasing grain size. The dielectric constant was found to be the highest for MnFe2O4 with a particle size of 18.1 nm because of low strain value of 0.028 and high X-ray density value of 5.11. Therefore, a sample with the highest dielectric properties is a sample with grain size of 18.1 nm with real dielectric constant of 311; imaginary of 118; and impedance of 328 kΩ at 10 kHz. The frequency variation of (εʹ and ε”) is explained by Knop phenomenological theory and hopping of electrons between Fe 2+ and Fe 3+ on octahedral sites.