Ferroelectric Morphotropic Phase Boundary Research Articles

Inducing a magnetic morphotropic phase boundary in (0.7) BiNdxFeO3-(0.3)BaTiO3 (0 ≤ x ≤ 0.05) system

Multiferroics materials processing ferroelectric and magnetic properties are being explored widely for device applications around the world. Herein, a composite multiferroic material was designed which is expected to show enhanced magnetoelectric (ME) multiferroic properties. In this unique idea, a lead free (0.7)BiFeO3-(0.3)BaTiO3 system with ferroelectric morphotropic phase boundary (MPB) was chosen and a magnetic MPB is induced through Nd incorporation. The MPB was confirmed through X-ray diffraction and Raman studies. The hysteresis loops confirmed the ferroelectric nature of solid solutions and the increase in polarization is related to the induced structural changes. A consistent increase in magnetization with Nd content indicates weaking of R3c symmetry of BiFeO3 due to continuous suppression of the spiral spin structure leading to transition from antiferromagnetic to ferromagnetic response. The presence of ferroelectric and ferromagnetic nature along with the existence of MPB indicates that solid solutions are promising candidates for magnetoelectric multiferroic applications.

Effect of local compositional heterogeneity on the piezoelectric property at ferroelectric morphotropic phase boundary – A phase field study

In this work, the effect of local compositional heterogeneity on the domain structure and piezoelectricity at ferroelectric morphotropic phase boundary (MPB) is studied by phase field simulations. It is found that the local compositional heterogeneity leads to a unique domain structure at MPB, i.e., a mixture of tetragonal, monoclinic and rhombohedral domains. Although polarization rotation occurs for both MPB samples with and without local compositional heterogeneity, the piezoelectric d33 coefficient becomes reduced for the sample with local compositional heterogeneity because polarization rotation becomes more difficult on average. This work unravels the effect of local compositional heterogeneity on the piezoelectric property of ferroelectric MPB.

Topology of ferroelectric phase diagrams with morphotropic phase boundary and their piezoelectric properties

ABSTRACT Ferroelectric materials at morphotropic phase boundary (MPB) exhibit large piezoelectric coefficients and thus are widely used as piezoelectric actuators and sensors. Three different phase diagram topologies have been reported in various ferroelectric MPB systems: one with a cubic(C)-tetragonal(T)-orthorhombic(O)-rhombohedral(R) quadruple point; another with a C-T-R triple point and the other with a C-T-R along with a T-O-R triple point. However, it is unclear which phase diagram topology would give the best piezoelectric property. Here in this work, we obtain the above three different MPB phase diagram topologies by Landau free energy. It was found that among the three phase diagram topologies, the one with a T-O-R triple point exhibits superior piezoelectric property at the T-O-R triple point because of the small polarization anisotropy required by the simultaneous thermodynamic equilibrium of three ferroelectric phases. This work could guide the design of piezoelectric materials.

Polarization Spinodal at Ferroelectric Morphotropic Phase Boundary.

Here, we report a new phenomenon of uniform and continuous transformation of a single polarization domain into alternating nanodomains of two polarization vectors with the same magnitude but different directions at ferroelectric morphotropic phase Boundary (MPB). The transformation is fully reversible and could enhance the piezoelectric coefficient d_{33}. Further free energy calculations illustrate that such a polarization "decomposition" process occurs within the region on the Landau free energy curve with respect to the polarization direction where the second derivative becomes negative, which is similar to spinodal instability in phase transformations such as spinodal ordering or isostructural phase separation (e.g., spinodal decomposition). This "polarization spinodal" uncovers a new mechanism of polarization switching that may account for the ultrahigh ahysterestic piezoelectric strain at the MPB. This work could shed light on the development of phase transition theory and the design of novel ferroelectric memory materials.

Phase field simulation of grain size effects on the phase coexistence and magnetostrictive behavior near the ferromagnetic morphotropic phase boundary

The grain size effects on the phase coexistence and magnetostrictive response of Tb1−xDyxFe2 polycrystals near the ferromagnetic morphotropic phase boundary (MPB) are revealed through phase-field modeling. It shows that phase coexistence is a universal phenomenon in polycrystals for both ferromagnetic and ferroelectric MPB and that the range of compositions for phase coexistence increases with decreasing grain sizes. A large, reversible, and anhysteretic magnetostrictive response at low external fields is also found in the fine-grained polycrystals around the ferromagnetic MPB, which offers us a route to developing nanocrystalline magnetostrictive materials.

Rhombohedral-Orthorhombic Ferroelectric Morphotropic Phase Boundary Associated with a Polar Vortex in BiFeO3 Films.

Strongly correlated oxides exhibit multiple degrees of freedoms, which can potentially mediate exotic phases with exciting physical properties, such as the polar vortex recently found in ferroelectric oxide films. A polar vortex is stabilized by competition between charge, lattice, and/or orbital degrees of freedom, which displays vortex-ferroelectric phase transitions and emergent chirality, making it a potential candidate for designing information storage and processing devices. Here, by a combination of controlled film growth and aberration-corrected scanning transmission electron microscopy, we obtain nanoscale vortex arrays in [110]-oriented BiFeO3 films. These vortex arrays are stabilized in ultrathin BiFeO3 layers sandwiched by two coherently grown orthorhombic scandate layers, exhibiting a ferroelectric morphotropic phase boundary constituted by a mixed-phase structure of polar orthorhombic BiFeO3 and rhombohedral BiFeO3. Clear polarization switching and piezoelectric signals were observed in these multilayers as revealed by piezoresponse force microscopy. This work presents a feature of a polar vortex in BiFeO3 films showing morphotropic phase boundary character, which offers a potential degree of manipulating phase components and properties of ferroelectric topological structures.

Role of the electronic structure in the morphotropic phase boundary of TbxDy1−xCo2 studied by first-principle calculation

Physically parallel to ferroelectric morphotropic phase boundary, a phase boundary separating two ferromagnetic phases of different crystallographic symmetries was experimentally found in TbxDy1−xCo2 via high-resolution synchrotron X-ray diffraction. However, lack of the theoretical support makes the morphotropic phase boundary in ferromagnetic system debatable. Here, a first-principle calculation was employed to investigate the electronic structure variation during the morphotropic phase transition in TbxDy1−xCo2. It offers a theoretical basis for the ferromagnetic phase of different crystallographic symmetries in TbxDy1−xCo2. It also provides an explanation for why morphotropic phase boundary occurs in TbxDy1−xCo2 alloys and offers a serviceable method to search for the morphotropic phase boundary phenomena in other alloys via computational rather than experimental method.

Coexisting ferroelectric and magnetic morphotropic phase boundaries in Dy-modified BiFeO3-PbTiO3 multiferroics

Morphotropic phase boundary (MPB) in ferroelectric solid solutions can significantly enhance the dielectric and piezoelectric performances of the materials. Similarly, magnetic MPB has been found to exist in a few ferromagnets and is proved to be greatly beneficial to the magnetostrictive response. In this letter, we report the finding of a magnetic MPB in the multiferroic 0.66Bi1−xDyxFeO3-0.34PbTiO3 system, which overlaps the structural MPB of ferroelectric phases. A (weak) ferromagnetic state is induced at room temperature by Dy for the rhombohedral compositions with x ≥ 0.10. Upon cooling down from room temperature, the tetragonal compositions (x ≤ 0.05) show only one magnetic phase transition from the paramagnetic to antiferromagnetic phase, while the rhombohedral compositions exhibit a series of magnetic phase transitions from the (weak) ferromagnetic state to an antiferromagnetic order then to another weak ferromagnetic phase. A magneto-structural phase diagram has been established that reveals the presence of a magnetic MPB and a ferroelectric MPB. More significantly, the ferroelectric and magnetic MPB regions are found to overlap with each other, pointing to interesting kinds of multiferroic couplings.

Extensive domain wall motion and deaging resistance in morphotropic 0.55Bi(Ni1/2Ti1/2)O3–0.45PbTiO3 polycrystalline ferroelectrics

Domain wall motion is known as a major source of extrinsic contributions to the dielectric and piezoelectric properties of ferroelectric materials. In the present work, we report the extent of non-180° domain wall motion during strong and weak electric field amplitudes in situ using time-resolved, high-energy X-ray diffraction in the ferroelectric morphotropic phase boundary composition 0.55Bi(Ni1/2Ti1/2)O3–0.45PbTiO3 (BNT-45PT). After application of strong electric fields, two phases are shown to coexist. In the tetragonal phase of this material, the extent of 90° domain wall motion is significant and the domain alignment is nearly saturated. Weak (subswitching) cyclic electric fields are then also shown to induce domain wall motion. Deaging, or the progressive loss of preferred domain orientation during sequentially increasing field amplitudes, is notably low in these materials, showing that the initial domain alignment is strongly stabilized. Overall, the in situ measurements reveal that domain wall motion significantly impacts the structure and properties of BNT-45PT and reinforces the importance of understanding domain wall motion contributions to the physical properties of ferroelectrics.

Morphotropic Phase Boundaries in Ferromagnets:Tb1−xDyxFe2Alloys

The structure and properties of the ferromagnet Tb(1-x)Dy(x)Fe(2) are explored through the morphotropic phase boundary (MPB) separating ferroic phases of differing symmetry. Our synchrotron data support a first order structural transition, with a broadening MPB width at higher temperatures. The optimal point for magnetomechanical applications is not centered on the MPB but lies on the rhombohedral side, where the high striction of the rhombohedral majority phase combines with the softened anisotropy of the MPB. We compare our findings with single ion crystal field theory and with ferroelectric MPBs, where the controlling energies are different.

Deaging and Asymmetric Energy Landscapes in Electrically Biased Ferroelectrics

In ferroic materials, the dielectric, piezoelectric, magnetic, and elastic coefficients are significantly affected by the motion of domain walls. This motion can be described as the propagation of a wall across various types and strengths of pinning centers that collectively constitute a force profile or energetic landscape. Biased domain structures and asymmetric energy landscapes can be created through application of high fields (such as during electrical poling), and the material behavior in such states is often highly asymmetric. In some cases, this behavior can be considered as the electric analogue to the Bauschinger effect. The present Letter uses time-resolved, high-energy x-ray Bragg scattering to probe this asymmetry and the associated deaging effect in the ferroelectric morphotropic phase boundary composition 0.36BiScO3 - 0.64PbTiO3.

Ferroelectric phases and relaxor states in the novel lead-free (1 − x) Bi1/2K1/2TiO3 − x BiScO3 system (0 ≤ x ≤ 0.3)

The novel lead-free Bi-based ferroelectric system with perovskite structure (1 − x) Bi1/2K1/2TiO3 − x BiScO3, chemically designed to show a ferroelectric morphotropic phase boundary (MPB) and high piezoelectric response, was synthesized by the conventional solid-state reaction method for compositions with 0 ≤ x ≤ 0.3. X-ray diffraction analysis shows that the samples possess perovskite-type structure for x < 0.3 and reveals a phase evolution in the symmetry from tetragonal for x < 0.1 to pseudocubic for 0.1 ≤ x ≤ 0.3. Electrical and piezoelectric properties of ceramic samples were systematically investigated, and results indicate that a ferroelectric MPB is not formed, but instead a transition from conventional ferroelectric to relaxor ferroelectric behavior occurs when increasing the (Bi, Sc) content between 5 and 10%. The origin of this unexpected effect, and its implications in the design of novel lead-free piezoelectric materials are discussed.

Effect of Sn:Ti variations on electric filed induced AFE–FE phase transition in PLZST antiferroelectric ceramics

The effect of Sn:Ti variations on antiferroelectric to ferroelectric phase transition of (Pb 0.97La 0.02)(Zr 0.65Sn 0.35− x Ti x )O 3 ( x = 0.08–0.11) ceramics with compositions near antiferroelectric to ferroelectric morphotropic phase boundary was studied. X-ray diffraction showed that all samples were tetragonal phase at room temperature. With the increase of x from 0.08 to 0.1, all samples showed the typical antiferroelectric double loops. The critical value E AF of the electric-field induced antiferroelectric to ferroelectric phase transition decreased from 64 kV/cm to 38 kV/cm, and the electric field E FA of induced-ferroelectric to antiferroelectric phase transition decreased from 44 kV/cm to 10 kV/cm. A high polarization of the sample with x = 0.1 can be induced with a lower electric filed. The variations of Sn:Ti ratio had no effect on hysteresis of Δ E (= E AF − E FA), but Δ E reduced with temperature increasing. The virgin sample of which x = 0.11 was intrinsic antiferroelectric phase, but the remanent polarization of induced-ferroelectric phase remained after electric-field was removed at room temperature.

Development And Modification Of Photorefractive Properties In The Tungsten Bronze Family Crystals

The Sr1-xBaxNb2O6 (SBN) and Ba2-xSrxK1-yNayNb5O15 (BSKNN) tungsten bronze solid-solution systems are shown to be promising photo-refractive materials. Because of the versatility of the bronze structure, both the response time and spectral response can be controlled by altering the type of dopant and its crystallographic site preference. This paper reviews the current status of the tungsten bronze crystals SBN and BSKNN for photorefractive applications in terms of their growth, electro-optic character, and the role of cerium dopants. Ferroelectric morphotropic phase boundary (MPB) bronze materials are also discussed as potentially important for future development.