Evolution of crystal structure and ferroic properties of La-doped BiFeO3 ceramics near the rhombohedral-orthorhombic phase boundary

Bi1−xLaxFeO3 ceramics (0.15 ⩽ x ⩽ 0.2) across the rhombohedral-orthorhombic phase boundary have been studied using X-ray and neutron diffraction, magnetization measurements and piezoresponse force microscopy (PFM). The regions of structural stability of the polar, anti-polar and non-polar phases have been identified depending on the dopant concentration and a temperature and the structural phase diagram has been further clarified. The factors influencing phase transitions (size effects, chemical bonds peculiarities, local chemical inhomogeneities, etc.) have been estimated. PFM measurements testified a maximal piezoelectric response for a compound with the dominant rhombohedral phase in a metastable state. Magnetic properties have been discussed assuming weak ferromagnetic state with a major contribution from the orthorhombic phase. An evolution of structural parameters across the phase boundary decisive for improved ferroelectric and magnetic properties has been analyzed.

► Phase diagram as a function of La concentration and temperature has been specified.
► Dominant role of the orthorhombic phase in remanent magnetization is revealed.
► Maximal piezoelectric response is specific to metastable rhombohedral phase.
► Increased piezoelectric signal is explained by intrinsic and extrinsic contributions.