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Abstract
The phase transitions and domain structure of the promising PbO-free solid solution series, (0.95-x)BiFeO3-xLaFeO3-0.05La2/3TiO3, were investigated. X ray diffraction (XRD) revealed a transition from a ferroelectric R3c to a PbZrO3-like (Pbam) antiferroelectric (AFE) structure at x = 0.15 followed by a transition to a paraelectric (PE, Pnma) phase at x > 0.30. The ferroelastic/ferroelectric twin domain width decreased to 10–20 nm with increasing x as the AFE phase boundary was approached but coherent antiphase tilted domains were an order of magnitude greater. This domain structure suggested the local symmetry (20 nm) is lower than the average structure (R3c, a−a−a−) of the tilted regions. The PE phase (x = 0.35) exhibited a dominant a−a−c+ tilt system with Pnma symmetry but diffuse reflections at ∼1/4{ooe} positions suggest that short range antipolar order is residual in the PE phase. The complex domain structure and phase assemblage of this system challenge the conventional interpretation of phase transitions based on macroscopic symmetry. Instead, it supports the notion that frustration driven by chemical distributions at the nanometric level influences the local or pseudo-symmetry as well as the domain structure, with XRD giving only the average macroscopic structure.
Highlights
BiFeO3 (BFO) is one of the most extensively researched perovskite compounds because of its room temperature multiferroic properties
X ray diffraction (XRD) revealed a transition from a ferroelectric R3c to a PbZrO3-like (Pbam) antiferroelectric (AFE) structure at x 1⁄4 0.15 followed by a transition to a paraelectric (PE, Pnma) phase at x > 0.30
The complex domain structure and phase assemblage of this system challenge the conventional interpretation of phase transitions based on macroscopic symmetry
Summary
BiFeO3 (BFO) is one of the most extensively researched perovskite compounds because of its room temperature multiferroic properties. It is simultaneously ferroelectric (FE) with a Curie temperature, TC % 1100 K,1 and antiferromagnetic (AFM) with a Neel temperature, TN % 643 K.2. Polarization versus electric field loops do not saturate due to a combination of high Curie temperature (TC) and conductivity.[9]. As a room temperature multiferroic, BFO is an obvious choice for applications such as multiple state memory elements, electric field controlled magnetic resonance devices, and transducers with magnetically modulated piezoelectricity.[10]. One of the issues currently facing BFO is that the multiferroic properties are inaccessible due to its antiferromagnetic nature, which leads to cancellation of macroscopic magnetization and generally hinders linear magnetoelectric coupling.[11]. The processing of phase-pure BFO is very difficult and is usually associated with parasitic phases such as Bi25FeO39 and Bi2Fe4O9, due in part to the volatile nature of Bi2O3.12
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