Superlattice induced by electron-beam irradiation in magnetic ferroelectric BiMnO3

Single-phased polycrystalline BiMnO3 (hereinafter abbreviated as BMO) ceramic was fabricated via high-pressure solid-state reaction. Microstructure modification of selective grains, signalled by emergence of superlattice diffraction, was scrutinized by means of electron diffraction (ED) combined with high-resolution transmission electron microscopy (HRTEM). It was clearly evidenced that the well established C2 monoclinic substructure (a = 9.53 angstrom, b = 5.61 angstrom, c = 9.85 angstrom and beta = 110.67 degrees) of BMO (Atou et al 1999 J. Solid State Chem. 145 639) is metastable and prone to be transformed to a new pseudocubic superstructure (a approximate to b approximate to c approximate to 15.8 angstrom and a alpha approximate to beta approximate to gamma approximate to 90 degrees) (Yang et al 2006 Phys. Rev. B 73 024114) when irradiated continuously by an electron beam. Magnetization measurement unveiled a unique ferromagnetic phase transition at 103 K, which corroborated our speculation that as-prepared BMO ceramic is free of polymorphism at ambient conditions.