Critical roles of Mn-ions in enhancing the insulation, piezoelectricity and multiferroicity of BiFeO3-based lead-free high temperature ceramics

A lead-free multiferroic ceramic of BiFe0.96Sc0.04O3-BaTiO3 is a type of ABO(3) perovskite structure, belonging to the R3c space group, but exhibiting poor insulation and weak multiferroicity. In this work, the critical roles of Mn-ions in tailoring the electrical and magnetic properties of BiFeO3-based materials are revealed: the introduction of MnO2 into BiFe0.96Sc0.04O3-BaTiO3 induces a dramatic improvement in insulation, piezoelectricity and multiferroicity. New compositions of BiFe0.96Sc0.04O3-BaTiO3 + x mol% MnO2 were synthesized by a conventional solid-state reaction method. All the ceramics possess a perovskite structure, and a morphotropic phase boundary (MPB) of rhombohedral and monoclinic phases is formed at x = 0.5-1.0. The formation of Fe-Fe3+(2+) and V-O2-(center dot center dot) is noticeably suppressed and the resistivity of the ceramics is increased by similar to 100 times after the addition of 0.5-1.0 mol% MnO2, which make the ceramic polarizable and thus give strong ferroelectricity and considerable piezoelectricity. The ceramics with the MPB composition exhibit high electrical insulation (R = 1.2-1.7 x 10(10) Omega cm), good piezoelectricity (d(33) = 123-143 pC N-1, k(p) = 0.34-0.35), strong ferroelectricity (P-r = 13.1-17.6 mu C cm(-2)), high Curie temperature (590-596 degrees C) and excellent temperature stability of piezoelectric and ferroelectric properties. These improvements are greatly associated with the contribution of Mn-ions in the ceramics. Surprisingly, sharply enhanced ferromagnetism with M-r = 0.4946 emu g(-1) and M-s = 1.0298 emu g(-1) is obtained in the ceramic with x = 7.0, almost one thousand times larger than that of an un-doped ceramic. The origin of unusual ferromagnetism is associated with significant changes in magnetic ordering caused by Mn doping. The high magnetoelectric effect (alpha(33) = 429.6 mV cm(-1) Oe(-1)) is obtained after the addition of 2.0 mol% Mn ions. Our study suggests that the present ceramics may have potential applications in advanced memory devices as promising lead-free high temperature piezoelectric and multiferroic materials.