Structure of ceramics treated with hot-pressing

BiFeO3 ceramics synthesized at high temperature and pressure is observed to possess large spontaneous polarization and magnetism. The selected-area electron diffraction patterns indicate the coexistence of polycrystalline and nanocrystalline grains in the hot-pressed samples. Raman spectroscopic studies reveal that the Bi–O bond strain and cations (Fe3+) away from the oxygen octahedral center induce the polarization. The Fe–O bond strain, oxygen octahedral rotation around the [111] axis, and electromagnons build a long-range interaction between electrical polarization and magnetic moment reorientation to form an incommensurate spiral magnetic structure. This work clearly shows that the hot-pressed treatment can modify the structure and properties of BiFeO3 ceramics.