MICROWAVE SYNTHESIS OF BISMUTH ORTHOPHERRITE

Abstract

Nanocrystals, thin films, heterostructures based on nanoscale bismuth ferrite, a ferroelectric with high Curie temperatures (1123 K) and the antiferromagnetic Neel point (643 K) are promising as high-efficiency magneto-electric materials. Solid phase synthesis of materials based on ferrites due to their refractoriness requires a long time and high temperatures up to 1500 °C, which leads to a significant increase in the energy intensity of the synthesis processes. It is a pressing challenge to synthesize multifunctional nanomaterials based on bismuth ferrite using simple and low-cost methods. The main purpose of this work is to develop and optimize the synthesis of BiFeO₃ nanopowder using microwave and ultrasonic radiation. The choice of the crystalline hydrates Fe(NO₃)₃∙9Н₂О and Bi(NO₃₎₃·5H₂O as precursors is conditioned by the intensive absorption of microwave radiation by water molecules due to their significant dipole moment and the ability to reorient and rotate under microwave action. Microwave radiation stimulates decomposition of salt precursors, dehydration and synthesis of bismuth ferrite due to homogeneity and high speed of microwave heating and acceleration of the processes of the "nucleation" under the influence of "nonthermal" effects. Using the XRD and IRS methods, optimal parameters of BiFeO₃ synthesis have been established, which makes it possible to obtain chemically homogeneous samples without Bi₂O₃: precipitant – NaOH, microwave exposure time (power 700 W) is 15 minutes, ultrasonic treatment is 10 minutes, thermal annealing at 500 °C is 2 hours. The size of the coherent scattering regions of bismuth ferrite samples synthesized at these parameters is in the range of 54-80 nm, the average value is 67 nm. The TEM method has shown that the BiFeO₃ nanoparticles synthesized under these conditions have a shape close to spherical and they have a fairly narrow dispersion in size (35-60 nm). The developed technique of bismuth ferrite synthesis activated by microwave and ultrasonic radiation significantly reduces the time and energy intensity of the process in comparison with solid-phase synthesis and ensures high chemical homogeneity of the product.

ACKNOWLEDGEMENTS

The reported study was supported by a grant from the Russian Foundation for Basic Research (project No. 16-43-360595 r_a).

The research was carried out using the equipment of the Centre for Collective Use of Scientific Equipment of Voronezh State University.