Bismuth ferrite suffers from high leakage currents and the presence of a complex incommensurate spin cycloidal magnetic ordering, which has limited its commercial viability and has led researchers to investigate the functionality of doped BiFeO3 ceramics. In particular, the substitution of rare earths onto the Bi3+ site of the perovskite lattice have been shown to lead to improved functional properties, including lower leakage currents and the suppression of the magnetic spin cycloid. There is particular interest in materials with compositions close to structural morphotropic phase boundaries, because these may lead to materials with enhanced electronic and magnetic properties analogous to the highly relevant PbZrO3– PbTiO3 solid solution. However, many contradictory crystal structures and physical behaviors are reported within the literature. To understand the structure–property relationships in these materials, it is vital that we first unravel the complex structural phase diagrams. We report here a comprehensive review of structural phase transitions in rare-earth-doped bismuth ferrite ceramics across the entire lanthanide series. We attempt to rationalize the literature in terms of the perovskite tool kit and propose an updated phase diagram based on an interpretation of the literature.

Composition-driven structural phase transitions in rare-earth-doped bifeo 3 ceramics: a review

A lead-free multiferroic ceramic of BiFe0.96Sc0.04O3–BaTiO3 is a type of ABO3 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 and is noticeably suppressed and the resistivity of the ceramics is increased by ∼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 × 1010 Ω cm), good piezoelectricity (d33 = 123–143 pC N−1, kp = 0.34–0.35), strong ferroelectricity (Pr = 13.1–17.6 μC cm−2), high Curie temperature (590–596 °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 Mr = 0.4946 emu g−1 and Ms = 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 (α33 = 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.

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

Effect of Dy-substitution on structural, electrical and magnetic properties of multiferroic BiFeO3 ceramics

Structural, dielectric and impedance characteristics of (Bi0.5Na0.5)TiO3-BaTiO3 electronic system

Phase transition and conduction mechanism of rare earth based tungsten-bronze compounds

A new ferroelectric oxide Li2Pb2Pr2W2Ti4Nb4O30: Synthesis and characterization

Dielectric and impedance spectroscopy of BiFeO3–NaTaO3 multiferroics

Detailed studies of electrical and resistive properties of Bi2NdTiVO9 (a member of the Aurivillius family), fabricated by a method of standard high-temperature solid-state reaction, are discussed here. The compound crystallizes in the orthorhombic crystal structure. The surface morphology studies show a uniform distribution of grains. The single semicircle of the complex impedance plot and the value of the nonlinear coefficient of the J∼E graph suggest that the polarization in the material is due to grain effect only. The semiconducting nature (i.e., negative temperature coefficient of resistance) is observed in the temperature dependence of bulk resistance and J–E characteristics of the sample. The frequency dependence of impedance and electrical modulus of the material shows the existence of non Debye-type of relaxation. The activation energy obtained from the relaxation and conduction processes is found to support the activation of oxygen vacancies in the compound. An analysis of ac conductivity, based on the Jonscher’s power law, suggests that the conduction mechanism in the material can be explained using CBH model (i.e., hopping of oxygen ions between vacancies). The nature and existence of electric field dependent polarization (P–E hysteresis loop) at room temperature show that the material has ferroelectric property.

R.N.P. Choudhary

Papers

Phase transition and conduction mechanism of rare earth based tungsten-bronze compounds

A new ferroelectric oxide Li2Pb2Pr2W2Ti4Nb4O30: Synthesis and characterization

Dielectric and impedance spectroscopy of BiFeO3–NaTaO3 multiferroics

Structural, dielectric, impedance and modulus spectroscopy of Bi 2 NdTiVO 9 ferroelectric ceramics

Ferroelectric and ferromagnetic properties of Gd-modified BiFeO3