Processing and properties of Yb-doped BiFeO3 ceramics

Abstract

The authors prepared Yb-doped bismuth iron oxide ceramics ͑Bi 1−x Yb x FeO 3 , with 0 ഛ x ഛ 0.20͒ by rapid liquid phase sintering method and investigated the material's structures and electrical properties. The x-ray diffraction measurements showed that the doping of Yb has induced noticeable lattice distortion in the ceramics, and a largest distortion was observed when the concentration of Yb was 15%. By doping electrical resistivity, ferroelectric and dielectric properties of the ceramics were improved. Among all samples, BiFeO 3 doped with 15% Yb was found to have the smallest leakage current density ͑Ͻ10 −7 A/cm 2 ͒ and the largest remnant polarization ͑8.5 C/cm 2 ͒. The compound BiFeO 3 ͑abbreviated as BFO͒ was first synthesized in the late 1950s. 1 Research in the early stage, which mainly focused on ceramics, revealed that BFO possesses a rhombohedrally distorted perovskite structure ͑lat-tice parameters a = b = c = 0.563 nm and ␣ = ␤ = ␥ = 59.4°͒ in addition to coupled ferroelectric ͑Curie temperature T C ϳ 1103 K͒ and antiferromagnetic ͑Neel temperature T N ϳ 643 K͒ behaviors at room temperature. Despite a high Curie temperature, the bulk BFO exhibits very weak ferroelectric behavior ͑e.g., the spontaneous polarization P s , is only ϳ3.5 C/cm 2 ͒. 2-5 BFO thin films have been studied since the late 1980s. 6 In 2003, Wang et al. reported that a very large ferroelectric polarization ͑remnant polarization P r ϳ 60 C/cm 2 ͒ has been achieved in a BFO thin film epitaxially grown on SrRuO 3 / SrTiO 3 . 7 The significantly enhanced polarization was interpreted as the result of a compressive stress imposed by the SrRuO 3 electrode, which has an in-plane lattice parameter smaller than that of BFO. Because of the compressive stress, the epitaxial BFO film has a tetragonal-like crystal structure ͑a = 0.394 nm, c = 0.400 nm, and ␣ = 89.5°͒ rather than the rhombohedral symmetry in bulk materials and therefore leads to large polarization. Since then more studies have reported with successful development of BFO thin films with polarizations ranging from 50 to 150 m/cm 2 . 2,8-10 Theoretical work has also been conducted to interpret the extraordinarily large ferroelectric polarization in BFO films. 11 The success in the thin film studies has in turn stimulated interest to produce bulk ceramics with improved properties. New processing techniques, such as rapid liquid phase sintering, have been developed to synthesize single-phase BFO ceramics. 12,13 The effect of compositional modification, either by forming of solid solution ͑e.g., with Pb͑Zr 1−x ,Ti x ͒O 3 ͒ 14 or by doping, has also been extensively studied. Quite a number of transition metal elements ͑e.g., Ni, Ti, Cr, and Mn͒ 15-18 and rare-earth elements ͑e.g., La and Nd͒ 19,20 have been employed as dopants. The authors are more interested in the doping of rare-earth elements because this may significantly change both the ferroelectric properties and magnetic behaviors of BFO which could possibly lead to enhanced magnetoelectric effect. 21,22 In this work, we repo...

Effect of Ba ions substitution on multiferroic properties of BiFeO3 perovskite

“…In a ferroelectric, dielectric constant is determined by the polarization. The substitution of Bi with Ba leads to increase in lattice distortion and therefore results in enhanced polarization upto x=0.2, which leads to the increase of dielectric constant [21]. Further increase in Ba concentration leads to decrease in lattice distortion which results in decrease in polarization along with a decrease in dielectric constant.…”

“…A coercive field (H C ) of 0.907 kOe for x=0.1, 1.907 kOe for x=0.2 and1.837 kOe for x=0.3 is observed respectively. Compared with some doped BiFeO 3 compounds [12,13,20,21,24,25], these Ba doped BiFeO 3 ceramics exhibit larger magnetization at room temperature. This spontaneous magnetization of Ba doped BiFeO 3 ceramics might originate from the rhombohedral distorted perovskite structure (space group R3c) of BiFeO 3 , in which both ferroelectric atomic displacements and a weak ferromagnetic ordering might be allowed due to the canting spin arrangement [4].…”

Observation of room temperature saturated ferroelectric polarization in Dy substituted BiFeO3 ceramics

“…14,15 In the present investigation, high quality Dy substituted BFO ceramics have been prepared by sintering the corresponding precursor powders at 780 C. The sintering temperature is greatly decreased by comparing it with that used in traditional solid state reaction methods (usually beyond 850 C [Refs. [11][12][13][14][15][16][17]) and even lower than the melting point of Bi 2 O 3 (which melts at a temperature slightly above 800 C [Ref. 20]).…”

“…[11][12][13][14][15] However, the RT ferroelectricity in bulk BFO still raises many questions. Some BFO-based ceramics have been considered to exhibit weak ferromagnetism and ferroelectricity simultaneously, [12][13][14][15][16][17] but supporting evidences for ferroelectric properties are mostly indirect characteristics. The most indisputable means to substantiate the ferroelectric properties of a material is to measure its polarization hysteresis loops.…”

Studies on structural, electrical and magnetic properties of Dy-doped BiFeO3 thin films

“…Generally, several reasons can be used to explain the enhanced magnetization for the various ions doped BFO films. First, ions doping can change the magnetic structure of BFO due to the canting of the antiferromagnetic sublattices, which is induced by structural distortion or structural transition [32,33]. From the XRD, Rietveld refinement and Raman spectra analysis, Dy doping leads to the structural transition from trigonal with R3c: H space group to trigonal with R3m: R space group in the BD x FO films.…”