In complex oxide heteroepitaxy, strain engineering is a powerful tool to obtain phases in thin films that may be otherwise unstable in bulk. A successful example of this approach is mixed phase bismuth ferrite (BiFeO3) epitaxial thin films. The coexistence of a tetragonal-like (T-like) matrix and rhombohedral-like (R-like) striations provides an enhanced electromechanical response, along with other attractive functional behaviors. In this paper, we compare the energetics associated with two thickness dependent strain relaxation mechanisms in this system: domain walls arising from monoclinic distortion in the T-like phase, and the interphase boundary between the host T-like matrix and tilted R-like phases. Combining x-ray diffraction measurements with scanning probe microscopy, we extract quantitative values using an empirical energy balance approach. The domain wall and phase boundary energies are found to be 113 $\pm$ 21 and 426 $\pm$ 23 mJ.m$^{-2}$, respectively. These numerical estimates will help us realize designer phase boundaries in multiferroics, which possess colossal responses to external stimuli, attractive for a diverse range of functional applications.
We investigate, using density functional theory, how the interaction between the ferroelectric polarization and the chemical structure of the (001) surfaces of bismuth ferrite influences the surface properties and reactivity of this material. A precise understanding ofthe surface behavior of ferroelectrics is necessary for their use in surface science applications such as catalysis as well as for their incorporation in microelectronic devices. Using the (001) surface of bismuth ferrite as a model system we show that the most energetically favoured surface geometries are combinations of surface…
Single phase barium titanate-bismuth ferrite ((1-x)BaTi$_3$-(x)BiFe$_3$, BTO-BFO) solid solutions were prepared using citric acid and ethylene glycol assisted sol-gel synthesis method. Depending on the dopant content the samples are characterized by tetragonal, tetragonal-pseudocubic, pseudocubic and rhombohedral structure as confirmed by Raman spectroscopy and XRD measurements. An increase of the BFO content leads to a reduction in the cell parameters accompanied by a decrease in polar distortion of the unit cell wherein an average particle size increases from 60 up to 350 nm. Non zero piezor…
University of Duisburg-Essen（杜伊斯堡-埃森大学）；European Organization for Nuclear Research (CERN)（欧洲核子研究组织（CERN））；Universidade de Aveiro（阿威罗大学）；Institute for Research in Fundamental Sciences (IPM)（基础科学研究所（IPM））
Bismuth ferrite is one of the most widely studied multiferroic materials because of its large ferroelectric polarisation coexisting with magnetic order at room temperature. Using density functional theory (DFT), we identify several previously unknown polar and non-polar structures within the low-energy phase space of perovskite-structure bismuth ferrite, BiFeO$_3$. Of particular interest is a series of non-centrosymmetric structures with polarisation along one lattice vector, combined with anti-polar distortions, reminiscent of ferroelectric domains, along a perpendicular direction. We discuss…
We study the effects of bismuth doping on the crystal structure and phase transitions in single crystals of the perovskite semiconductor methylammonium lead tribromide, MAPbBr3. By measuring temperature-dependent specific heat capacity (Cp) we find that, as Bi doping increases, the phase transition assigned to the cubic to tetragonal phase boundary decreases in temperature. Furthermore, after doping we observe one phase transition between 135 and 155 K, in contrast to two transitions observed in the undoped single crystal. These results appear strikingly similar to previously reported effects …
Multiferroics in which giant ferroelectric polarization and magnetism coexist are of tremendous potential for engineering disruptive applications in information storage and energy conversion. Yet the functional properties of multiferroics are thought to be affected detrimentally by the presence of point defects, which may be abundant due to the volatile nature of some constituent atoms and high temperatures involved in materials preparation. Here, we demonstrate with theoretical methods that oxygen vacancies may enhance the functionality of multiferroics by radically changing their magnetic in…
Phase transitions in multiferroic BiFeO3 crystals, thin-layers, and ceramics: Enduring potential for a single phase, room-temperature magnetoelectric 'holy grail'
Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independently from the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscope allows for local implantation and patterning down to the nanometer resolution, which is of interest for device applications. We present here a study of bismuth ferrite (BiFeO3) films where strain was patterned locally by helium implantation. Our combined Raman, XRD and TEM study shows that the implantation causes an elongation of the BiFeO3 unit cell and ultimately a transition towa…
Quantum metric quadrupoles in elemental bismuth thin films
Università di Salerno（萨莱诺大学）；Helmholtz-Zentrum Dresden-Rossendorf e.V.（德累斯顿-罗森多夫亥姆霍兹中心）；Maynooth University（梅努斯大学）；Institute for Theoretical Solid State Physics, IFW Dresden and Würzburg-Dresden Cluster of Excellence ct.qmat（德累斯顿IFW理论固体物理研究所及维尔茨堡-德累斯顿卓越集群ct.qmat）；TU Dortmund University（多特蒙德工业大学）
Spatially modulated morphotropic phase boundaries in a compressively strained multiferroic thin film
University of Southern California（南加州大学）；University of Michigan, Dearborn（密歇根大学迪尔伯恩分校）；University of California, Berkeley（加州大学伯克利分校）；Cornell University（康奈尔大学）
