Abstract: Porous bismuth ferrite ceramics were synthesized by sacrificial pore former method. A mixture of BiFeO3 and 20 wt% of various pore formers including high density polyethylene, polyethylene glycol, polyvinyl alcohol, urea and graphite was intensively milled for 10 h in a planetary ball mill, uniaxially cold pressed and then subjected to the multi-stage heat treatment. The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure. Density and porosity measurements showed that by employing 20 wt% of high density polyethylene and graphite, a porous sample with a maximum porosity of nearly 40% could be obtained. Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7 μm, uniform pore distribution as well as interconnected pores. Moreover, reactions between BiFeO₃ matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO₃ phase in the final porous samples. Analysis of X-ray diffraction patterns illustrated that in the samples processed with graphite, high density polyethylene and polyvinyl alcohol as pore former, BiFeO₃ matrix phase partially or completely decomposed to intermediate phases of Bi₂Fe₄O₉ and Bi₂₅FeO₄0. Using of urea did not damage the matrix phase and porous BiFeO₃ within the original perovskite structure could be prepared. Furthermore, thermodynamic investigation was carried out for prediction of possible interactions between matrix phase and pore former at elevated temperatures.

Key words: Multiferroic, Bismuth ferrite, Porous ceramics, Sacrificial pore former, Porosity, Phase composition