Morphotropic Boundary Research Articles

Constructing Morphotropic Phase Boundary in Epitaxial BiFeO3 on SrTiO3 by Suppression of Strain Relaxation

AbstractThe strain‐driven morphotropic boundary in BiFeO3 can enhance the piezoelectric properties. However, the tetragonal phase has generally been observed in BiFeO3 films grown on substrates with intense compressive strain (more than −4.5%) within a limited thickness range (<300 nm) due to significant thickness‐dependent strain relaxation during film growth at high deposition temperatures. This work proposes suppressing thickness‐dependent strain relaxation by decreasing growth temperature. Utilizing a hydrothermal method, the growth temperature of epitaxial BiFeO3 films decreases to 200 °C. As a result, the tetragonal phase is observed in 600‐nm‐thick BiFeO3 film on (001) SrTiO3 substrates (strain equals only −1.5%), accompanied by the monoclinic phase. This SrTiO3‐available morphotropic phase boundary significantly enhances the piezoelectric response in epitaxial BiFeO3 film. Ex situ and in situ measurements, theoretical calculations, and simulation confirm that the SrTiO3‐available morphotropic phase boundary originates from the suppressed strain relaxation. Furthermore, a critical temperature (400 °C), below which the tetragonal phase can be maintained, is identified to offer an applicable strategy for extending strain‐driven morphotropic phase boundary for high‐performance piezoelectric films.

BiFeO3 and BiMnO3 co-dopant in morphotropic boundary of BNT-BT ceramics: study on phase structure and ferro/piezo-electric properties

BiFeO3 and BiMnO3 co-dopant in morphotropic boundary of BNT-BT ceramics: study on phase structure and ferro/piezo-electric properties

Role of Nb5+-Nd3+ co-dopant in morphotropic boundary of electrospun PZT nanoneedles: Study on dielectric and piezoelectric sensitivity

This study focused on the effects of individual and simultaneous modification of electrospun PZT nanostructures with doping by Niobium (Nb5+) and Neodymium (Nd3+) cations. The SEM, EDS, XRD, XPS, STA, and TEM analyses were performed to identify the role of the donor-acceptor on the morphology, crystallography, and morphotropic boundary (MPB) of PZT nanostructures. The results indicated that the nanowhiskers of PZT were formed after post-calcination at 800 ℃ for 2 h. The morphology of the nanowhiskers was not changed drastically with individual doping by Nb and Nd while co-doping caused to morphology switch to the nanoneedles. The perovskite PZT phase; Pb(Zr0.58Ti0.42)O3 (Zr-rich, rhombohedral) phase was achieved with doping by Nb, while Pb(Zr0.52Ti0.48)O3 (Ti-rich, tetragonal) was determined with doping by Nd. With the de-convolution of the Zr 3d spectrum of XPS, it was exhibited that the nearest composition to MPB was attributed to Nb-Nd co-doped PZT. The polycrystalline fiber arranged by tetragonal-rhombohedral was observed. It was also found that the concentration of oxygen vacancy was reduced with doping by Nb, while increased with doping by Nd. The dielectric properties of un-doped and doped PZT were investigated. The dielectric constant of PZT was increased with individual doping by Nb and Nd, while due to the donor-acceptor couple, a synergistic effect was observed for co-doping by Nb-Nd where maximum dielectric was 16 times higher than the un-doped PZT. Also, with measuring the output voltage, the highest piezoelectric sensitivity was observed in the Nb-Nd co-doped PZT sample. Our findings highly suggest the electrospinning method for achieving the nanostructured PZT to be employed in a variety of applications needs a high dielectric constant.

Фазовые состояния твердого раствора (1-x)PbFe-=SUB=-0.5-=/SUB=-Nb-=SUB=-0.5-=/SUB=-O-=SUB=-3-=/SUB=--xPbTiO-=SUB=-3-=/SUB=-. Описание на основе многоминимумных моделей

Based on the composition of two multiminimum models, a statistical model has been developed on the basis of which the formation of tetragonal and monoclinic ferroelectric phases in a solid solution (1-x)PbFe0.5Nb0.5O3-xPbTiO3 has been investigated and described. By selecting the parameters of the model, it was possible to reproduce the diagram T(x) of this solid solution. The peculiarity of the diagram is that when approaching the concentration of x~0.1, the temperatures of the phase transitions between the tetragonal and monoclinic phases decrease sharply, turning to zero. It is shown that the disappearance of the monoclinic phase is due to the specifics of the statistical properties of the eight-minimum model describing the subsystem of octahedra with eight minima. The features of the thermodynamic properties of a solid solution in the vicinity of the morphotropic boundary between the tetragonal and monoclinic phases are also investigated

Phase transitions in the ferroelectric relaxor (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 close to the morphotropic phase boundary

Structural transformations of unpoled $(1\ensuremath{-}x)\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3\ensuremath{-}x}\mathrm{PbTi}{\mathrm{O}}_{3}\phantom{\rule{0.28em}{0ex}}(\mathrm{PMN}\text{\ensuremath{-}}\mathrm{PT})$ single crystals ($x=0.28$ and $x=0.32$) were analyzed by calorimetry and acoustic spectroscopy. The compositions are close to the morphotropic boundary (MPB). We find extended two-phase regions where cubic and rhombohedral ($x=0.28$), cubic and tetragonal, tetragonal and monoclinic phases ($x=0.32$) coexist during cooling and heating. The observed structural transitions in PMN-PT are first order, despite their proximity to the MPB. The predicted tricritical points, if they exist, are possibly located extremely close to the MPB.

Braiding Lateral Morphotropic Grain Boundaries in Homogenetic Oxides.

Interfaces formed by correlated oxides offer a critical avenue for discovering emergent phenomena and quantum states. However, the fabrication of oxide interfaces with variable crystallographic orientations and strain states integrated along a film plane is extremely challengingby conventional layer-by-layer stacking or self-assembling. Here, the creation of morphotropic grain boundaries (GBs) in laterally interconnected cobaltite homostructures is reported. Single-crystalline substrates and suspended ultrathin freestanding membranes provide independent templates for coherent epitaxy and constraint on the growth orientation, resulting in seamless and atomically sharp GBs. Electronic states and magnetic behavior in hybrid structures are laterally modulated and isolated by GBs, enabling artificially engineered functionalities in the planar matrix. This work offers a simple and scalable method for fabricating unprecedented innovative interfaces through controlled synthesis routes as well as providing a platform for exploring potential applications in neuromorphics, solid-state batteries, and catalysis.

Morphotropic Relaxor Boundary Construction Highly Boosts the Piezoelectric Properties of Bi-Based Lead-Free Thin Films.

To achieve large electrostrain and low hysteresis, we further optimized a morphotropic phase boundary (MPB) by modulating its local polar symmetries. The construction of a morphotropic relaxor boundary (MRB) in thin films can be achieved by suitable introduction of Bi(Fe0.95Mn0.03Ti0.02)O3 into (Bi0.5Na0.5)TiO3-SrTiO3 to form a solid solution. The designed thin film achieves surprising piezoelectric properties with an inverse piezoelectric coefficient of 179.7 pm V-1 and negligible hysteresis. The composition of two relaxors with different local polar symmetries (tetragonal nanoregions and rhombohedral nanoregions), namely, an MRB, and the coexistence of multiscale domain structures can greatly weaken the anisotropy of polarization, degrade the energy barrier, attenuate the discontinuity of polarization, and achieve a large electrostrain and low hysteresis. The domain dynamics of the PNRs under the action of an external excitation field are analyzed to clarify the enhancement mechanism. This construction of MRBs is feasible for producing lead-free piezoelectric films with high-voltage electrical properties and low hysteresis, and various experimental design and theoretical references are provided.

Enhanced ferroelectric and piezoelectric response by MnO2 added Bi0.5(K0.2Na0.8)0.5TiO3 ceramics

Morphotropic phased boundary (MPB) existent Bi0.5(K0.2Na0.8)0.5TiO3:xwt%MnO2 (BKNT:xMn) ceramic system is fabricated to investigate the ferroelectric and piezoelectric properties. All the ceramic samples have maintained the tetragonal (P4mm)-rhombohedral (R3c) structural duality due to MPB regional investigation of BKNT. The addition of MnO2 in BKNT has improved the multifunctional properties of the material at x ​= ​0.15. BKNT:0.15Mn ceramic has shown the maximum density of 6.98 ​g/cm3, remnant polarization (Pr) ​∼ ​32.5 ​μC/cm2, high impedance of ∼108 ​Ω, d33 of 206 ​pC/N, which are much improved properties than pure single phase BKNT and Bi0.5K0.5TiO3 ceramics. The dependence of dielectric constant (εr) on temperature suggests the relaxor behavior and the high Curie temperature (TC) ​∼ ​410 ​°C for BKNT:0.15Mn ceramic, higher than the TC ​∼ ​360 ​°C of pure BKNT ceramic. The poled ceramics have maintained the stable piezoelectric properties till 300 ​°C. The introduction of multivalence Mn has improved the multifunctional properties of the material significantly, making it a strong candidate to be utilized in actuators and sensors.

A combined theoretical and experimental study of the phase coexistence and morphotropic boundaries in ferroelectric-antiferroelectric-antiferrodistortive multiferroics

The physical nature of the ferroelectric (FE), ferrielectric (FEI) and antiferroelectric (AFE) phases, their coexistence and spatial distributions underpins the functionality of antiferrodistortive (AFD) multiferroics in the vicinity of morphotropic phase transitions. Using Landau-Ginzburg-Devonshire (LGD) phenomenology and a semi-microscopic four sublattice model (FSM), we explore the behavior of different AFE, FEI, and FE long-range orderings and their coexistence at the morphotropic phase boundaries in FE-AFE-AFD multiferroics. These theoretical predictions are compared with the experimental observations for dense Bi1-yRyFeO3 ceramics, where R is Sm or La atoms with the fraction 0 ≤ y ≤ 0.25, as confirmed by the X-ray diffraction (XRD) and Piezoresponse Force Microscopy (PFM). These complementary measurements were used to study the macroscopic and nanoscopic transformation of the crystal structure with doping. The comparison of the measured and calculated AFE/FE phase fractions demonstrate that the LGD-FSM approach well describes the experimental results obtained by XRD and PFM for Bi1-yRyFeO3. Hence, this combined theoretical and experimental approach provides further insight into the origin of the morphotropic boundaries and coexisting FE and AFE states in model rare-earth doped multiferroics.

Designed morphotropic relaxor boundary ceramic exhibiting large electrostrain and negligible hysteresis

Electromechanical materials with large electrostrain and low hysteresis are strongly desired for high-precision actuator applications. Despite extensive studies for more than half a century, it is still a challenge to obtain large electrostrain and low hysteresis simultaneously due to the so-called strain-hysteresis trade-off. Here, we report a mechanism to overcome this trade-off: a ceramic composition locating at a morphotropic relaxor boundary (MRB), exhibits enhanced electrostrain and reduced hysteresis as compared with off-MRB compositions. The MRB, a composition-induced boundary separating two relaxors with different local polar symmetries, is attained by transforming an morphotropic phase boundary (MPB) in Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) through doping lanthanum. The performances of large electrostrain of 0.227% and negligible hysteresis of 3% of MRB composition are the best, as evidenced by occupying a virgin region in the strain-hysteresis chart of relaxor electromechanical ceramics. Moreover, this MRB ceramic maintains the large electrostrain and low hysteresis over a temperature range from 35 to -35 °C. The understanding of abnormal effects of MRB is established through combining microstructure observations and Landau theory analysis: the MRB composition with morphotropic nanodomain structure and higher degree of local structural heterogeneity shows a flatter energy profile with much lower energy barrier, thereby leading to a large electrostrain and negligible hysteresis. Our work demonstrates that the MRB is an effective mechanism to design relaxor materials with large electrostrain and low hysteresis simultaneously. We predict that more high-performance MRB electromechanical materials will be found in properly doped MPB systems.

Geometrical frustration and piezoelectric response in oxide ferroics

Ferroic perovskite oxides remain a major topic of interest in material science and condensed matter physics. Their versatile structure can accommodate many transition metal ions leading to a variety of useful properties, such as, among others, ferroelectricity. Several mechanisms behind the ferroelectricity of perovskites have been proposed. Using advanced x-ray scattering techniques and 3D modeling, the increased piezoelectric response of the exemplary sodium-potassium niobate ferroics is shown to arise from the presence of local fluctuations in the tilt pattern of the constituent niobium-oxygen octahedra. The result implies that the search for perovskite ferroics with increased functionality need not necessarily concentrate on systems exhibiting a morphotropic boundary and/or distinct polar nanodomains. Inducing local structural disorder in a controlled manner, e.g. through measured metal ion substitution, may become worthwhile.

Morphotropic Relaxor Boundary in a Relaxor System Showing Enhancement of Electrostrain and Dielectric Permittivity.

In ferroelectric and relaxor-ferroelectric materials, piezoelectric and dielectric properties are significantly enhanced at the morphotropic phase boundary (MPB), a boundary between different ferroelectric phases with different macroscopic symmetries. By contrast, in relaxor systems, such an MPB does not exist because relaxors of different compositions possess the same macroscopic symmetry. Here, we report the existence of a morphotropic relaxor boundary (MRB) in the single phase relaxor region of a K_{0.5}Na_{0.5}NbO_{3}-xBaTiO_{3} system, which is a composition-induced boundary between two relaxors with different local polar symmetries (tetragonal versus rhombohedral) but with the same macroscopic cubic symmetry. At the MRB the electrostrain increases by ∼3 times and the permittivity increases by ∼1.5 times over a wide temperature range of more than 100K, as compared with off-MRB compositions. Our Letter demonstrates that the MRB may become an effective mechanism to enhance the dielectric and electrostrictive properties of relaxors.

THE USE OF THE PROFILE ANALYSIS OF DIFFRACTION PEAKS FOR DETERMINATION OF THE PHASE RELATIONSHIPS IN THE SYSTEM (1 -2<i>x</i>)BiScO<sub>3</sub> <i>x</i>PbTiO<sub>3</sub> • <i>x</i>PbMg<sub>1/3</sub>Nb<sub>2/3</sub>O<sub>3</sub> NEAR THE MORPHOTROPIC BOUNDAR

To determine the phase relationships in the system (1 - 2x)BiSc03 • xPbTi03 • xPbMg1/3Nb2/303 near the morphotropic boundary, the ceramic samples for x = 0.34 and x = 0.46 were studied by the XRD method. The profiles of nine regions of the XRD patterns were analyzed using WinFit software. In both cases, a much better agreement with the experimental data was observed with the introduction of additional phases with cubic symmetry. The simulation of the full x-ray diffraction patterns of the samples using the Le Bail method was also carried out. The studied samples contain two phases: the main with a cubic (o = 4.0432 A) (x = 0.34) and tetragonal (o = 3,9963 А, с = 4.0580 A) (x = 0.46) unit cells and additional one. The additional phases with broad diffraction peaks can be considered cubic (with the unit cell parameters a - 4.045 A and a - 4.017 A, respectively).

Polymorphic phase transition and morphotropic phase boundary in Ba1−x Ca x Ti1−y Zr y O3 ceramics

This paper deals with Ca and Zr co-doped BaTiO3 (BCTZ(x, y)) (x = 0.1, 0.13, 0.2 and y = 0.05, 0.1, 0.15). These ceramics were prepared using the conventional solid state method. The symmetry, dielectric properties, Raman spectroscopy, ferroelectric behavior and piezoelectric effect were examined. X-ray diffraction (XRD) results display that morphotropic boundary occurs from tetragonal to orthorhombic region of BCZT(x=0.1, 0.2, y=0.05, 0.1) and polymorphic phase transitions from tetragonal to orthorhombic, orthorhombic to rhombohedral regions of BCZT(x=0.13, y=0.1). The evolution of the Raman spectra was investigated as a function of compositions at room temperature, in correlation with XRD analysis and dielectric measurements. We note that the substitution of Ca in Ba site and Zr ions in Ti site slightly decreased the cubic-tetragonal temperature transition (T C) and increased the orthorhombic–tetragonal (T 1) and rhombohedral–orthorhombic (T 2) temperatures transitions. The ferroelectric properties were examined by a P–E hysteresis loop. The two parameters ΔT 1 and ΔT 2 are defined as ΔT 1 = T C − T 1 and ΔT 2 = T C − T 2, they come close to T C for x = 0.13, y = 0.1, which reveals that this composition is around the polymorphic phase. The excellent piezoelectric coefficient of d 33 = 288 pC N−1, the electromechanical coupling factor k p = 40%, high constant dielectric 9105, coercive field E c = 0.32 (KV mm−1) and remanent polarization P r = 0.1 (µc mm−2) were obtained for composition x = 0.13, y = 0.1.

Effects caused by antiferroelectric nanodomains in PZT-based coarse-grained ceramics with compositions from the morphotropic boundary region

Presented results demonstrate importance of taking into account such a phenomenon as the solid solution decomposition at the boundaries separating coexisting phases in lead zirconate-titanate-based solid solutions with compositions belonging to the morphotropic boundary region of the “temperature–composition” phase diagram. It is shown that in the local decomposition of solid solutions in the vicinity of the boundaries separating the tetragonal and rhombohedral phases in lead zirconate-titanate-based solid solutions lead to the changes of the solid solution’s chemical composition and to the formation of segregates. It is also shown that the proper thermoelectric treatment of samples containing these segregates can give substantially higher values of piezoelectric parameters in the lead zirconate-titanate-based compounds.

Composition Dependence of Crystal Structure, Electronic Structure, Ferroelectric and Piezoelectric Properties of (K,Na,Li)NbO3

INTRODUCTION Pb(Zr,Ti)O3-based piezoelectric ceramics have been widely used in electronic devices because of their excellent piezoelectric properties. Recently, owing to growing concern about environmental problems, the development of alternative piezoelectric ceramics is highly expected because Pb(Zr,Ti)O3 (PZT) contain a toxic element. (K,Na)NbO3(KNN) is one of the promising candidates.1) Superior characteristics of PZT is considered to be due to the morphotropic boundary (MPB), and KNN is also known to have a phase boundary similar to MPB. However, the characteristics and the crystal structure in the phase boundary are not well understood at the moment. It was also reported that substituting Li to the A-site of the perovskite structure ABO3 induces phase transition to tetragonal the KNN.2) From such backgrounds, we synthesized (K0.45Na0.55Lix)NbO3 and tried to reveal the composition dependence of the properties, the crystal and electronic structures in the phase boundary. In addition, we replaced the B-site by Ta, V and Mo partially, and then examined effects of the substitutions on the properties. EXPERIMENTAL Starting materials were wet-mixed in appropriate proportions, and then calcined in air for 2 h at 900 ℃. Thereafter, the samples were ground by a ball mill, and then sintered by the spark plasma sintering (SPS) method under a uniaxial pressing at 50 MPa for 5 min at 1050 ℃ in vacuum. For the obtained products, an recovery annealing treatment was performed at 900 ℃ for 4 h in O2. The identification of the phases and the evaluation of the lattice parameters were performed by XRD. Metal compositions of the ceramics were measured by ICP. Relative densities of the pellets were estimated by the Archimedes method. P-E hysteresis loop measurements were carried out at various frequencies using a TF-2000FE device (aixACCT) with the virtual ground mode. The surface and cross-section morphologies of the samples were observed by SEM. The temperature dependences of the dielectric permittivity (ε s ) and dielectric losses (tanδ) of the samples were measured by a LCR meter (HP-4284A). For average crystal structure analysis, we performed Rietveld analysis (RIETAN-FP) using synchrotron X-ray diffraction patterns.(BL19B2, spring-8) The electron densities were determined by the maximum entropy method (MEM) using the Dysnomia program. RESULTS AND DISCUSSION Figure 1 shows XRD patterns of (K0.45Na0.55Lix)NbO3 (x=0~0.07). These samples could be identified as the perovskite structures with the tetragonal (P4mm) and/or the orthorhombic (Amm2) symmetries. According to the crystal structure analysis by Rietveld method, in the composition of x=0.04~0.07, good fit can be obtained in a two-phase analysis of Amm2 and P4mm. These results indicate that there is a phase boundary around the composition range. It was found that all of the sample were sufficiently dense by the Archimedes method and the SEM observation. Measurements of P-Ehysteresis loop, the relative dielectric constant and dielectric loss demonstrated that the properties were improved in the x = 0.05~ 0.07. Such a change of the properties were examined from the electronic structure analysis by MEM and crystal structure analysis by Rietveld method. Further, we also investigated B-site substitution with a phase boundary, and evaluated their effect of the ferroelectric properties. REFERENCE 1)Y. Saito, et al. Nature, 432,84 (2004). 2) Hongliang Du, et al. Appl. Phys. Lett. 91, 182909 (2007). Figure 1

Crystal structure and piezoelectric and magnetic properties of Bi1–x Sm x FeO3 solid solutions

The crystal structure and piezoelectric and magnetic properties have been studied in Bi1‒xSmxFeO3 solid solutions with the compositions near the morphotropic boundary between rhombohedral and orthorhombic (Rh–Orh) phases. The coexistence areas of rhombohedral and antipolar orthorhombic phases, as well as the evolution of structural phases at the interface, have been established. A maximum piezoelectric signal is found for the two-phase composition with the dominating rhombohedral phase, and an increase in the piezoresponse is caused by the decreasing structural stability of the sample. The evolution of magnetic properties in Bi1–xSmxFeO3 compounds has been elucidated depending on the substitutional ion concentration. The orthorhombic phase composites are the weak ferromagnetics with the residual magnetization of ~0.2 emu/g.

Separate Kinetics of the Polar and Antiferrodistortive Order Parameters in the Antiferroelectric Transition of PbZr1-xTixO3 and the Influence of Defects

Abstract The transition from the rhombohedral-ferroelectric to the lower temperature orthorhombic-antiferroelectric phase in Zr-rich PZT involves two order parameters (OPs): 1) the polar OP for the displacements of the cations with respect to the O octahedra; 2) an antiferrodistortive OP responsible for tilting of the octahedra. It is shown that at Ti compositions near the morphotropic boundary with the FE phase (0.046 ≤ x ≤ 0.054), the two OPs may be almost independent of each other at cooling rates of 0.5 K/min or faster, depending on the sample history. This fact gives rise to a great variety of shapes of the curves of the elastic compliance s(T), but all of them can be fitted very well as superpositions of variously broadened steps for each of the modes involved in the transitions, including the tilt transition occurring in the untransformed FE fraction. The evolution of the s(T) curves includes enhancements up to a factor of four during aging for weeks in the region of the AFE/FE coexistence. Restiffening and reduction of the thermal hysteresis of the AFE/FE transition are recovered by heating up to 800-900 K. It is proposed that ageing is due to the clustering of relatively mobile defects, most likely O vacancies, at the domain walls in the coexisting AFE/FE phases. Such defect structures are probably at the origin of intense thermally activated relaxation processes observed above TC in the dielectric and anelastic spectra, and can be annealed out above 800 K, allowing the AFE transition to recover a fast kinetics.

Anomalously thick domain walls in ferroelectrics

Using the Landau theory we demonstrate the possibility of unusual, anomalously thick ferroelectric domain walls, where the order parameter rotates with a nearly constant modulus as in ferromagnets. The effect occurs in 90 degrees charged domain walls and is associated with the easy polarization rotation near the morphotropic phase boundary. This magneticlike profile is unique to charged domain walls due to the availability of free charges which screen the depolarizing field resulting from polarization rotation. In contrast to previously known thick ferroelectric domain walls, the large thickness of 90 degrees charged domain walls near the morphotropic boundary is predicted for a wide temperature interval. This property may be favorable for potential applications.

XRD and Raman spectroscopy studies of (Bi1–xLaxFeO3)0.5(PbTiO3)0.5 solid solution

(Bi1–xLaxFeO3)0.5(PbTiO3)0.5 solid solution obtained by mechanochemical synthesis was characterized by X-ray diffraction (XRD), atomic force microscopy and Fourier transform near-infrared Raman spectroscopy. The single-phase solid solution with La content between x = 0 and 0.5 was prepared. The solid solution exhibits a tetragonal symmetry P4mm for 0 ≤ x ≤ 0.2. It was found that Raman spectra undergo a significant change for the solid solution with La content between x = 0.16 and 0.20. It may indicate the existence of a morphotropic boundary in this range of the La content. Detailed XRD study on (Bi0.5La0.5FeO3)0.5(PbTiO3)0.5 pointed to a rhombohedral symmetry R3c.