Single Crystal Growth and Hierarchical Ferroelectric Domain Structure of (1- x)BiFeO₃- xPbTiO₃ Solid Solutions

Besides outstanding multiferroic performance, BiFeO₃ has recently demonstrated a potential for novel promising applications in domain wall nanoelectronics employing domain walls with different functional properties. Rarely observed in ferroelectrics, charged domain walls are of special interest for such applications as they possess enhanced electric conductivity. In this work, single crystals of the multiferroic (1-x)BiFeO₃-xPbTiO₃ solid solution were successfully grown using a flux method. Structural characterization by X-ray diffraction confirmed perovskite rhombohedral R3c and tetragonal P4mm phases in crystals with x ≈ 0.2 and x ≈ 0.6, respectively. The domain structure of crystals was established with the help of polarized light microscopy, scanning electron microscopy, and piezoresponse force microscopy. In tetragonal crystals, a complex hierarchical structure of 90° lamella domains is observed with the thickness of lamellae varying from dozens of nanometers to dozens of micrometers. In the rhombohedral composition, twin 109° domains are realized with the domain width of about several micrometers. Besides, the nano- and submicrometer sized rounded 180° domains are embedded randomly among twin domains in both tetragonal and rhombohedral crystals. Mechanical and electrical compatibility conditions are satisfied for all observed 90° and 109° domain walls. However, the 180° walls in tetragonal crystals are proved to be charged. Successful fabrication of high-quality single crystals with the desirable structures of charged and uncharged domain walls can enhance the multiferroic performance and also open a door to explore promising domain boundaries related phenomena.