Temperature and Composition-Induced Structural Transitions in Bi1-xLa (Pr)xFeO3 Ceramics

Bi1-xLaxFeO3 and Bi1-xPrxFeO3 ceramics of the compositions near the morphotropic phase boundary have been studied by X-ray and neutron diffraction techniques and differential thermal analysis. The structural phases characterized by the long-range polar, antipolar, and nonpolar ordering as well as the phase coexistence regions have been identified using the diffraction data depending on the dopant concentration and temperature. As a result of these studies the three phase region has been observed for the Pr-doped compounds and the phase diagrams have been constructed. The detailed evolution of the structural parameters permitted to itemize the factors affecting the structural phase transitions and clarify the origin of the enhanced electromechanical properties in these materials. The performed structural analysis disclosed different character of the chemical bonds in the La-and Pr-doped BiFeO3 compounds. Further, the role of the rare-earth ions in the covalency of the chemical bonds is discussed.