Sm-BFO STEM Datasets
Sm-doped BiFeO3 STEM datasets collected by Chris Nelson. Sample created at University of Maryland.
Nelson, Christopher↗
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Materials Data on FeBiO3 by Materials Project
BiFeO3 is Orthorhombic Perovskite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Fe3+ is bonded to six O2- atoms to form corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 32°. There are four shorter (2.06 Å) and two longer (2.07 Å) Fe–O bond lengths. Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.30–2.74 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Fe3+ and two equivalent Bi3+ atoms to form distorted corner-sharing OFe2Bi2 tetrahedra. In the second O2- site, O2- is bonded in a 5-coordinate geometry to two equivalent Fe3+ and three equivalent Bi3+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on FeBiO3 by Materials Project
BiFeO3 crystallizes in the tetragonal P4mm space group. The structure is three-dimensional. Fe3+ is bonded in a 5-coordinate geometry to five O2- atoms. There is one shorter (1.85 Å) and four longer (2.02 Å) Fe–O bond length. Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.32 Å) and four longer (2.83 Å) Bi–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Fe3+ and two equivalent Bi3+ atoms to form a mixture of distorted edge and corner-sharing OFe2Bi2 tetrahedra. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one Fe3+ and four equivalent Bi3+ atoms.
36 MATERIALS SCIENCE↗
Feasibility study of ferromagnetic/ferroelectric films for enhanced microwave devices
This report summarizes exploratory work conducted to assess the feasibility of ferromagnetic/ferroelectric films for next-generation microwave devices. From literature review, it is established that while an increasing number of ferroelectric/ferromagnetic composites are being investigated, a number have transition temperatures that are too low and structures that are not robust enough for low cost, room temperature antenna arrays. On the other hand, several promising systems are identified, including the multiferroic BiFeO3 and a composite system of Ba/SrTiO3 and a related perovskite manganite. It is suggested that when the NASA pulsed laser deposition chamber is fully operational, thin films of these systems be investigated. In preparation for such work, we have reconfirmed several structural features of an existing Ba/SrTiO3 film using the x-ray diffractometer at Oberlin College.
Ijiri, Yumi↗
Interfacial-Strain-Controlled Ferroelectricity in Self-Assembled BiFeO 3 Nanostructures
Self-assembled BiFeO 3 -CoFe 2 O 4 (BFO-CFO) vertically aligned nanocomposites are promising for logic, memory, and multiferroic applications, primarily due to the tunability enabled by strain engineering at the prodigious epitaxial vertical interfaces. However, local investigations directly revealing functional properties in the vicinity of such critical interfaces are often hampered by the size, geometry, microstructure, and concomitant experimental artifacts. Ferroelectric switching in the presence of lateral distributions of vertical strain thus remains relatively unexplored, with broader implications for all strain-engineered functional devices. Additionally, by implementing tomographic atomic force microscopy, 3D domain orientation mapping, and spatially-resolved ferroelectric switching movies, local tensile strain significantly impacts the ferroelectric switching, principally by retarding domain nucleation in the BFO nearest to the vertically epitaxial tensile-strained interfaces. The relaxed centers of the BFO pillars become preferred domain nucleation and growth sites for low biases, with up to an order of magnitude change in the edge:center switching ratio for high biases. The new, multi-dimensional imaging approach—and its corresponding insights especially for directly strained interface effects on local properties—thereby advances the fundamental understanding of polarization switching and provides design principles for optimizing functional response in confined nanoferroic systems.
36 MATERIALS SCIENCE↗
High and temperature-insensitive piezoelectric performance in the lead-free Sm-doped BiFeO 3 –BaTiO 3 ceramics with high Curie temperature
Large sensor piezoelectric constant (d 33 = 334 pC/N) and superior actuator piezoelectric constant (d 33 * = 552 pm/V) as well as a high Curie temperature (T C = 454 °C) were obtained simultaneously in the lead-free 0.67Bi 1.03 FeO 3 -0.33Ba 1-x Sm x TiO 3 ceramics. Such an excellent and temperature-insensitive piezoelectric performance with only 10% temperature variation of piezoelectric strain at the range of 25–125 °C is highly desirable for real applications. The structural origin of the enhanced piezoelectric performance is mainly attributed to the morphotropic phase boundary and the highest known tetragonality (c T /a T = 1.02) in such materials. Transmission electron microscopy and electro-mechanical phenomenological theory demonstrate that the superior d 33 and d 33 * are associated with the hybrids nanodomains (60–90 nm) and flattened thermodynamic energy profile owing to the local structure heterogeneity. Furthermore, these results are superior as the piezoelectric properties are temperature-independent and the material has large d 33 *, and high TC compared to other lead-free piezoelectric ceramics.
36 MATERIALS SCIENCE↗
A molecular dynamics study of domain switching in BiFeO 3 nanofilm under DC electric field
The performance of ferroelectric materials is deeply rooted in the domain switching process triggered by an applied electric field. To understand the effect of controlling factors on the domain switching characteristics, nanoscale studies are essential. In this work, an atomistic-scale computational framework is developed to study the domain switching process of bismuth ferrite (BiFeO 3 ) nanofilms. Through a series of molecular dynamics simulations, the effects of duration and magnitude of an electric field, domain size and nanofilm thickness on the domain switching behavior are investigated. The evolution of domains under different magnitudes and durations of the applied electric field is studied, and the results of unswitched and switched cases are summarized in a switching map. Analysis of various nanofilms reveals that by increasing the film thickness, the switching time is increased. Additionally, the nanofilms with different domain sizes and configurations are examined, and the minimum domain size for complete reversal switching is obtained. Our results are helpful to predict and tune the switching process in ferroelectric materials.
36 MATERIALS SCIENCE↗
Evidence of a glassy magnetic transition driven by structural disorder in BiFeO 3 nanoparticles
Important effects appear in low and high temperature magnetometry of multiferroic BiFeO 3 (BFO) nanoparticles as sizes are reduced from 105 nm to 18 nm. In these particles, a magnetic transition appears close to 200 K probably associated with a spin reorientation which is absent in bigger particles. At higher temperatures and up to the bulk ferroelectric Curie temperature (1000 K), two additional magnetic transitions can be identified. Around T N 600 K, a size-dependent magnetic transition appears, associated with an antiferromagnetic transition. A model based on atomic vibration instability can describe the variation of T N with nanoparticle size. Furthermore, for certain sizes, the properties are dominated by the glassy state arising from the disorder produced by the formation of a core-shell structure. This implies that the magnetic behavior of nanoparticles is strongly affected by their crystal structure close to the transition temperature. Finally, the structural disorder which couples to the magnetic properties add control to the magnetic and ferroelectric properties of BFO nanoparticles.
36 MATERIALS SCIENCE↗
Autonomous Multistate Nanoencoding Using Combinatorial Ferroelectric Closure Domains in BiFeO 3
Recent advances in ferroic materials have identified topological defects as promising candidates for enabling additional functionalities in future electronic systems. The generation of stable and customizable polar topologies is needed to achieve multistates that enable beyond-binary device architectures. Here, in this study, we show how to autonomously pattern on-demand highly tunable striped closure domains in pristine rhombohedral-phase BiFeO 3 thin films through precise scanning of a biased atomic force microscopy tip along carefully designed paths. By employing this strategy, we generate and manipulate closed-loop structures with high spatial resolution in an automated manner, allowing the creation of highly tunable and intricate topological domain structures that exhibit distinct polarization configurations without the need for electrode deposition or complex heterostructure growth. As a proof-of-concept for ferroelectric beyond-binary memory devices, we use such topological domains as multistates, engineering an alphabet and automating the symbolic writing/reading process using autonomous microscopy. The resulting information density is compared with that of current commercially available memory devices, demonstrating the potential of ferroelectric topological domains for multistate information storage applications.
BiFeO3↗