Optimization of functional properties of lead-free BiFeO3-BaTiO3

Abstract

In the present work, the optimization of synthesis conditions of lead-free (1-x)BiFeO3-xBaTiO3 (x being the mol fraction) solid solution is conducted to improve its functional properties. Two common routes to prepare this solid solution are given in the literature. In the first route, precursor oxides of Barium (BaCO3), Titanium (TiO2), Bismuth (Bi2O3) and Iron (Fe2O3) are mixed together and heat treated. While in the second route, Barium Titanate (BaTiO3) is used as a precursor and mixed with the Bismuth and Iron oxide and then heat treated. For this work, the second method was taken into consideration, which led to the synthesis of two BaTiO3 samples. These samples underwent a calcination process for 10 hours and 18 hours, respectively. Quantity of excess Bi2O3 is also added from 0 to 2 mol % while preparing solid solution samples to compensate for the bismuth volatilization effect. This led to the synthesis of five different samples. These samples were structurally characterized using synchrotron-based X-Ray Diffraction, which showed no signs of secondary phases, and the Le Bail fitting of XRD data proved the existence of Pm-3m and R3c phases together. Morphological characterization of these samples was done using field emission scanning electron microscopy, which revealed bimodal grains with grain boundaries. These two characterizations did not reveal any significant difference among these five samples. However, when electrical measurements were done, the (1-x)BF-xBT sample, which had been prepared using BaTiO3 for a shorter calcination period of 10 hours and had 1% excess Bi2O3 in it showed the highest dielectric constant of 32000 at 10kHz frequency and had lowest dielectric loss as well among five samples. Polarization- Electric Field loops showed similar results for this sample and exhibited typical ferroelectric response with remnant polarization of 32ℳC/cm2, the coercive field of 30 kV/cm, and saturated polarization of 40ℳC/cm2.