Flash sintering of bismuth ferrite in-situ using energy dispersive x-ray diffraction

Bismuth ferrite (BiFeO3, or BFO) is a multiferroic oxide ceramic that has unique properties at the nanoscale level at room temperature. For this reason, it is of great interest to study and implement BFO's properties for use in a variety of applications, including multiferroic memory, spintronics, and photovoltaics. However, BFO is difficult to make in bulk, not only because impurity phases can develop and inhibit its multiferroic properties, but also because the phase transition at 825°C from its ferroelectric to paraelectric state acts against the densification process. Flash sintering is a relatively new densification technique that takes less time and energy to make bulk ceramics while exposing the sample to a low electric field. In this study, we investigate the feasibility of flash sintering bismuth ferrite at temperatures below 825°C. Densification occurred at furnace temperatures of 500°C and 350°C, much lower than the transition temperature, to approximately 90% of the theoretical density. During this process, it was observed via energy dispersive X-ray diffraction, a rapid characterization technique used to probe crystallography of bulk materials, that anisotropic lattice expansion occurs when BFO is exposed to an electric field, which is not seen in conventional sintering. Estimating sample temperature during flash sintering is a difficult process, and a few methods are discussed. Finally, several theoretical models of flash sintering mechanisms are addressed to aid in understanding of how this technique works.Ph.D.Includes bibliographical referencesby Mary Anne Wasse