Recently, based on the phase-field modeling, it was predicted that Hf1-xZrxO2 (HZO) exhibits the morphotropic phase boundary (MPB) in its compositional phase diagram. Here, we investigate the effect of structural changes between tetragonal (t) and orthorhombic (o) phases on the ferroelectric and dielectric properties of HZO films to probe the existence of MPB region. The structural analysis show that by adjusting the ozone dosage during the atomic layer deposition process and annealing conditions, different ratios of t- to o-phases (f_(t/o) ) were achieved which consequently affect the ferroelectric and dielectric properties of the samples. Polarization versus electric field measurements show a remarkable increase in ferroelectric characteristics (Pr and Ec) of the sample that contains the minimum t-phase fraction (f_(t/o)~ 0.04). This sample shows the lowest dielectric constant compared to the other samples which is due to the formation of ferroelectric o-phase. The sample that contains the maximum f_(t/o)~ 0.41 demonstrates the highest dielectric response. By adjusting the f_(t/o), a large dielectric constant of ~ 55 is achieved. Our study reveals a direct relation between f_(t/o) and dielectric constant of HZO thin films which can be understood by considering the density of MPB region.
We report the finding of unusual scale-dependent symmetry below the ferroelectric Curie temperature in the perovskite Pb(Zr1-xTix)O3 single crystals of morphotropic phase boundary compositions. The crystals of tetragonal symmetry (from x-ray diffraction experiments) on sub-micrometer scale exhibit a macroscopic (optically determined) cubic symmetry. This peculiar optical isotropy is explained by the anomalously small size of tetragonal ferroelectric domains. Upon further cooling the crystals transform to the phase consisting of micrometer-sized domains of monoclinic Cm symmetry.
We investigate the microstructural evolution in a ferroelectric to antiferroelectric phase transition at the morphotropic phase boundary in the Bi(1-x)SmxFeO3 system. Continuous Sm3+ substitution on the A-site induces short-range anti-parallel cation displacements as verified by the appearance of localized 1/4(110) weak spots in selected area electron diffraction patterns for 0.1<x<0.14 samples, and thus onset of antiferroelectricity. Kinetic Monte Carlo simulations confirm that increasing the strength of the anti-parallel interactions (i.e. increasing x) induces a ferroelectric to antiferroel…
We report neutron inelastic scattering experiments on single crystal PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$ doped with 32\% PbTiO$_{3}$, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field $\mathbf{E} \parallel$ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to $\mathbf{E}$ weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to $\mat…
The contributory mechanisms associated with high piezoelectric response in piezoelectric ceramics have been examined by in-situ electric field dependent high energy synchro x-ray diffraction study. A comparative study of electric field induced lattice strain and the propensity for non-180o domain switching on two closeby compositions of a high performance piezoelectric alloy (1-x)PbTiO3-(x)BiScO3, one within the morphotropic phase boundary (MPB) region exhibiting d33 of 425 pC/N and another just outside the MPB region exhibiting d33 of 260 pC/N, unravelled that, inspite of the MPB specimen exh…
Many ferroelectric solid solutions exhibit enhanced electro-mechanical properties at the morphotropic boundary separating two phases with different orientations of polarization. The mechanism of properties enhancement is associated with easy paths for polarization rotation in anisotropically flattened free energy profile. Another mechanism of properties enhancement related to free energy flattening is polarization extension. It is best known at temperature-driven ferroelectric-paraelectric phase transitions and may lead to exceedingly large properties. Its disadvantage is temperature instabili…
A simple model to reproduce strong enhancement of dielectric response near the morphotropic phase boundary (MPB) is proposed. This model consists of long-range dipole-dipole interaction and compositional chemical disorder incorporated by the variation in lengths of dipole moments. By applying Monte Carlo simulation, we show that there appears a ferroelectric boundary phase between two types of antiferroelectric phases at an optimal strength of randomness. In the boundary phase, ferroelectric domain becomes remarkably large and flexible to external electric fields, leading to huge dielectric re…
The structural characteristics of the perovskite- based ferroelectric Pb(Zn1/3Nb2/3)O3-9%PbTiO3 at the morphotropic phase boundary (MPB) region (x≃0.09) have been analyzed. The analysis is based on the symmetry adapted free energy functions under the assumption that the total polarization and the unit cell volume are conserved during the transformations between various morphotropic phases. Overall features of the relationships between the observed lattice constants at various conditions have been consistently explained. The origin of the anomalous physical properties at MPB is discussed.
The physical nature of the ferroelectric (FE), ferrielectric (FEI) and antiferroelectric (AFE) phases, their coexistence and spatial distributions underpin 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 …
Morphotropic phase boundaries (MPBs) show substantial piezoelectric and dielectric responses, which have practical applications. The predicted existence of MPB in HfO2-ZrO2 solid solution thin film has provided a new way to increase the dielectric properties of a silicon-compatible device. Here, we present a new fabrication design by which the density of MPB and consequently the dielectric constant of HfO2-ZrO2 thin film was considerably increased. The density of MPB was controlled by fabrication of a 10-nm [1 nm-Hf0.5Zr0.5O2 (Ferroelectric)/1 nm-ZrO2 (Antiferroelectric)] nanolaminate followed…
We present an ab initio study of the BFCO solid solution formed by multiferroics BiFeO3 (BFO) and BiCoO3 (BCO). We find that BFCO presents a strongly discontinuous morphotropic transition between BFO-like and BCO-like ferroelectric phases. Further, for all compositions such phases remain (meta)stable and retain well-differentiated properties. Our results thus suggest that an electric field can be used to switch between these structures, and show that such a switching involves large phase-change effects of various types, including piezoelectric, electric, and magnetoelectric ones.
The symmetric studies on the structure-property relationship of the unpoled and poled states of 0.67BiFeO3-0.33BaTiO3 (0.67BF-0.33BT) were conducted to understand the origin of the morphotropic phase boundary (MPB) in BF-BT. A typical relaxor-type dielectric anomaly was observed (Tf, ~627 K). The remnant polarization (Pr) and maximum value of electro-strain (Sm) increase clearly during heating (Pr, ~40 uC/cm2; Sm, 0.191 % under 40 kV/cm at 453 K). The first-cycle electro-strain loops indicate the difference in the polar state between 0.67BF-0.33BT and 0.94BiNaTiO3-0.06BaTiO3. Both the unpoled …
Temperature-dependent dielectric permittivity of lead-free (LixNa1-x)NbO3 for nominal x = 0.04-0.20, prepared by solid state reaction followed by sintering, was studied to resolve often debated issue pertaining to exactness of morphotropic phase boundary (MPB) location along with structural aspects and phase stability in the system near MPB. Interestingly, a diffuse phase transition has been observed in the dielectric permittivity peak arising from the disorder induced in A-site and structural frustration in the perovskite cell due to Li substitution. A partial phase diagram has been proposed …
Physically parallel to ferroelectric morphotropic phase boundary, a phase boundary separating two ferromagnetic phase of different crystallographic symmetries was found in TbxDy1-xCo2. High-resolution synchrotron XRD has been carried out to offer experimental evidence for TbxDy1-xCo2. It has been proved that TbxDy1-xCo2 (0.6<x<0.7) is a morphotropic phase boundary and that the crystal structures of tetragonal (x<0.6) and rhombohedral (x>0.7) phase is distorted from a Laves Phase. Here, a first principles calculation provides a theoretical explanation on the origin of MBP in TbxDy1-xCo2 and is …
We report here the structure and dielectric studies on a new lead free (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution to explore the morphotropic phase boundary. The powder x-ray diffraction studies on (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution suggests that structure is tetragonal (P4mm) for the composition with x=0.05 and cubic for the composition with x=0.30 and 0.40. Morphotropic phase boundary is observed in the composition range 0.10<x<0.30, where phase coexistence is observed and composition dependence of room temperature permittivity shows a peak. High temperature dielectric measuremen…
Two-dimensional polarity is intriguing but remains in the early stage. Here a structural evolution diagram is established for GeS monolayer, which leads a noncollinear ferrielectric $δ$-phase energetically as stable as the ferroelectric $α$-phase. Its ferrielectricity is induced by the phonon frustration, i.e., the competition between ferroelectric and antiferroelectric modes, providing more routes to tune its polarity. Besides its prominent properties like large band gap, large polarization, and high Curie temperature, more interestingly, the morphotropic phase boundary between $α$- and $δ$-p…
Raman spectra of PbZr1-xTixO3 ceramics with titanium concentration varying between 0.40 and 0.60 were measured at 7 K. By observing the concentration-frequency dependence of vibrational modes, we identified the boundaries among rhombohedral, monoclinic, and tetragonal ferroelectric phases. The analysis of the spectra was made in the view of theory group analysis making possible the assignment of some modes for the monoclinic phase.
We report on the discovery of a lead-free morphotropic phase boundary in Sm doped BiFeO3 with a simple perovskite structure using the combinatorial thin film strategy. The boundary is a rhombohedral to pseudo-orthorhombic structural transition which exhibits a ferroelectric (FE) to antiferroelectric (AFE) transition at approximately Bi0.86Sm0.14FeO3 with dielectric constant and out-of-plane piezoelectric coefficient comparable to those of epitaxial (001) oriented Pb(Zr,Ti)O3 (PZT) thin films at the MPB. The discovered composition may be a strong candidate of a Pb-free piezoelectric replacement…
The structure and properties of the ferromagnet Tb_{1-x}Dy_xFe_2 (Terfenol-D) 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 f…
We present anelastic and dielectric spectroscopy measurements of PbZr(1-x)Ti(x)O(3) with 0.455 < x < 0.53, which provide new information on the low temperature phase transitions. The tetragonal-to-monoclinic transformation is first-order for x < 0.48 and causes a softening of the polycrystal Young's modulus whose amplitude may exceed the one at the cubic-to-tetragonal transformation; this is explainable in terms of linear coupling between shear strain components and tilting angle of polarization in the monoclinic phase. The transition involving rotations of the octahedra below 200 K is visible…
We report neutron inelastic scattering on single crystal 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3 (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB). Data were obtained between 100 K and 600 K under zero and non-zero electric field applied along the cubic [001] direction. The lowest energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however the square of the soft mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the s…
A first-principles-derived approach is used to study structural, piezoelectric and dielectric properties of Pb(Zr_{1-x}Ti_{x})O_{3} (PZT) solid solutions near the morphotropic phase boundary at low temperature. Three ferroelectric phases are found to exist: a tetragonal phase for larger x compositions, a rhombohedral phase for smaller x compositions, and the recently discovered monoclinic phase in between. In this monoclinic phase, the polarization associated with the Zr atoms behaves differently from the polarization associated with the Ti atoms. As the composition x decreases, the former rot…
Using data obtained from first-principles calculations, we show that the position of the morphotropic phase boundary (MPB) and transition temperature at MPB in ferroelectric perovskite solutions can be predicted with quantitative accuracy from the properties of the constituent cations. We find that the mole fraction of PbTiO$_3$ at MPB in Pb(B$'$B$''$)O$_3$-PbTiO$_3$, BiBO$_3$-PbTiO$_3$ and Bi(B$'$B$''$)O$_3$-PbTiO$_3$ exhibits a linear dependence on the ionic size (tolerance factor) and the ionic displacements of the B-cations as found by density functional theory calculations. This dependenc…
A monoclinic phase was recently discovered near the morphotropic phase boundary in several high-performance piezoelectric perovskite solid solutions, but its properties have not been reported. In this paper the dielectric, piezo- and ferroelectric properties of the monoclinic Pm phase in the (1-x)Pb(Mg1/3Nb2/3)O3 -xPbTiO3 perovskite system are studied. In a (001)-oriented crystal of composition x=0.33, ferroelectric hysteresis loops with remanent polarization of 23 uC/cm^2 are displayed. In poled monoclinic crystals, under unipolar drive up to 10 kV/cm, the domain walls remain unchanged, the p…
Enhanced room-temperature electromechanical coupling in the lead-free ferroelectric system $(1-x)$BaZr$_{0.2}$Ti$_{0.8}$O$_{3}$ - $x$Ba$_{0.7}$Ca$_{0.3}$TiO$_{3}$ (abbreviated as BZCT) at $x=0.5$ is attributed to the existence of a morphotropic phase region (MPR) containing an intermediate orthorhombic ($O$) phase between terminal rhombohedral ($R$) BZT and tetragonal ($T$) BCT phases. However, there is ambiguity regarding the morphotropic phase transition in BZCT at room temperature - while some experiments suggest a single $O$ phase within the MPR, others indicate coexistence of three polar …
Temperature dependent structural changes in a nearly pure monoclinic phase composition (x=0.525) of Pb(Zr_xTi_1-x)O_3 (PZT) have been investigated using Rietveld analysis of high-resolution synchrotron powder x-ray diffraction data and correlated with changes in the dielectric constant and planar electromechanical coupling coefficient. Our results show that the intrinsic piezoelectric response of the tetragonal phase of PZT is higher than that of the monoclinic phase. It is also shown that the high piezoelectric response of PZT may be linked with an anomalous softening of the elastic modulus (…
The complex elastic compliance and dielectric susceptibility of (Na_{0.5}Bi_{0.5})_{1-x}Ba_{x}TiO_{3} (NBT-BT) have been measured in the composition range between pure NBT and the morphotropic phase boundary included, 0 <= x <= 0.08. The compliance of NBT presents sharp peaks at the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the tetragonal region of the phase diagram, up to now impossible due to the strong lattice disorder and small distortions and polarizations involved. In spite of ample evidence of disorder and structural heterogeneity, the R-T t…
The competitions between ferroelectric and rotational instabilities in rhombohedral PZT near x = 0.5 are investigated using first principles density functional supercell calculations. As expected, we find a strong ferroelectric instability. However, we also find a substantial R-point rotational instability, close to but not as deep as the ferroelectric one. This is similar to the situation in pure PbZrO_3. These two instabilities are both strongly pressure dependent, but in opposite directions so that lattice compression of less than 1% is sufficient to change their ordering. Because of this, …
For decades it has been a well-known fact that among the few ferroelectric compounds in the perovskite family namely BaTiO3, KNbO3, PbTiO3 Na1/2Bi1/2TiO3 the dielectric and piezoelectric properties of BaTiO3 is considerably higher than the others in polycrystalline form at room temperature. Further, similar to ferroelectric alloys exhibiting morphotropic phase boundary, single crystals of BaTiO3 exhibits anomalously large piezoelectric response when poled away from the direction of spontaneous polarization at room temperature. These anomalous features in BaTiO3 remained unexplained so far from…
We present here the results of the room temperature dielectric constant measurements and Rietveld analysis of the powder x-ray diffraction data on $(1-x)[Pb(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$(PMN-$x$PT) in the composition range $0.20 \leq x \leq 0.45$ to show that the morphotropic phase boundary (MPB) region contains two monoclinic phases with space groups Cm (or $M_B$ type) and Pm (or $M_C$ type) stable in the composition ranges $0.27 \leq x \leq 0.30$ and $0.31 \leq x \leq 0.34$, respectively. The structure of PMN-$x$PT in the composition ranges $0 \leq x \leq$ 0.26, and $0.35 \leq x \leq1$ is …
It appeared worthwhile to us to present a state-of-the-art look at the field of ferroelectrics. We are certainly not attempting to provide a complete review of all aspects of the field of ferroelectrics over the last years but we wish to transport a flavour of the current excitement in the field through the (subjective) choice of four specific examples of current interest: (i) Piezoelectrics and the morphotropic phase boundary, (ii) Multiferroics, (iii) The effect of high pressure on ferroelectrics and (iv) Strain-engineering in ferroelectric oxide thin films. For each topic we will try to wor…
Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB), at which the relevant material's properties approach their maximum. Based on a synchrotron x-ray diffraction study of MPB PZT, bulk fatigue is unambiguously found to arise from a less effective field induced tetragonal-to-monoclinic transformation, at which the degradation of the polarization flipping is detected by a less intense and more diffuse anomaly in the atomic displacement parameter of lead. The time dependence of the ferroelectric response…
Relaxor ferroelectrics are complex materials with distinct properties different from classic ferroelectrics. Probing frequency depended dielectric susceptibility is its trait. Other empirical laws build on classic ferroelectrics are still applicable to relaxor ferroelectrics. Here we report an abnormal improved dielectric in La doped relaxor ferroelectric 0.4PNN-0.6PHT, which deviated from the consistent variation relationship with piezoelectric coefficient. A mesoscale mechanism is proposed to reveal the origin of the improved dielectric response in 0.4PNN-0.6PHT, where the polar nanoregions …
A dielectric nonlinear response in model two-phase composites, prepared from a displacive ferroelectric material with a dominant dielectric response due to a single oscillator ferroelectric mode and a dielectric material, is characterized by the existence of new modes due to geometric resonances below the percolation threshold in the ferroelectric matrix. The geometric nature of oscilations depends on composition and geometric properties of the mixture. Generation of higher frequency modes is studied within our model and discussed for displacive ferroelectric materials of the $BaTiO_{3}$ type.…
We report the ferroelectric property in Tb2Ti2O7 pyrochlore, prepared by a two-step solid-state reaction method. A concave P-E (polarisation vs electric field) loop observed from 382 K confirms ferroelectricity, below which the loop remains as pointed or banana-shaped. Dielectric plots clearly show an anomaly at 383 K and the magnetic data reveals a deviation from 380 K supporting the observed ferroelectric ordering. The origin of ferroelectricity in Tb2Ti2O7 is discussed which is due to the structural distortion in TiO6 octahedron.
Here, we report the unusual behaviour shown by the (BiFeO3)1-x-(PbTiO3)x (BF-xPT) films prepared using a multilayer deposition approach by chemical solution deposition method. Thin film samples of various compositions were prepared by depositing several bilayers of BF and PT precursors by varying the BF or PT layer thicknesses. X-ray diffraction showed that final samples of all compositions show mixing of the two compounds resulting in a single phase mixture, also confirmed by transmission electron microscopy. In contrast to bulk equilibrium compositions, our samples show a monoclinic (MA type…
We calculate the pyrocoefficient, static dielectric susceptibility profiles and its thickness dependence of ferroelectric thin films. Also, the temperature dependences of above quantities have been calculated. For the calculations we use Landau phenomenological theory, leading to Lame equations. These equations subject to boundary conditions with different extrapolation length on the surfaces have been solved numerically. The divergency of pyroelectric coefficient and static dielectric susceptibility in the vicinity of thickness induced ferroelectric phase transition (i.e. at $l\approx l_c$ or…
We report here the presence of three coexisting ferroelectric phases in a lead-free lithium sodium niobate (Li$_{x}$Na$_{1-x}$NbO$_{3}$; LNNx) system stable for $0.15 \leq x \leq 0.80$, which contrasts the review report of Dixon and Lightfoot [Phys. Rev. B $\textbf{97}$, 224105 (2018)]. More importantly, we have identified LNN20 as an important composition for technological applications due to its high dielectric permittivity, low loss, and high ferroelectric response. The anomalous dielectric and ferroelectric responses in LNN20 have been attributed to the morphotropic phase boundary like nat…
Though the electrical responses of the various polymorphs found in ferroelectric polycrystalline thin film HfO$_2$ are now well characterized, little is currently understood of this novel material's grain sub-structure. In particular, the formation of domain and phase boundaries requires investigation to better understand phase stabilization, switching, and interconversion. Here, we apply scanning transmission electron microscopy to investigate the atomic structure of boundaries in these materials. In particular, we find orthorhombic/orthorhombic domain walls and coherent orthorhombic/monoclin…
An analysis of the dynamic dielectric and electro-optic relaxation response of thin film ferroelectrics is presented. The analysis is based upon the relaxation of ferroelectric domains with a continuous distribution of sizes given by percolation theory. The resulting temporal response is described by the expression (t^-m) exp(-(t/tau)^beta). The analysis was applied to KNbO3 thin films. Measurements of the polarization, birefringence and dielectric transients show qualitative agreement with the model over 11 orders of magnitude in time.
We report far-infrared dielectric properties of powder form ferroelectric SrTiO3. Terahertz time-domain spectroscopy (THz-TDS) measurement reveals that the low-frequency dielectric response of SrTiO3 is a consequence of the lowest transverse optical (TO) soft mode TO1 at 2.70 THz (90.0 1/cm), which is directly verified by Raman spectroscopy. This result provides a better understanding of the relation of low-frequency dielectric function with the optical phonon soft mode for ferroelectric materials. Combining THz-TDS with Raman spectra, the overall low-frequency optical phonon response of SrTiO…
In this work, we address the issue of peaking of piezoelectric response at a particular composition in the morphotropic phase boundary (MPB) region of (Pb0.940Sr0.06)(ZrxTi1-x)O3 (PSZT) piezoelectric ceramics. We present results of synchrotron x-ray powder diffraction, dielectric, piezoelectric and sound velocity studies to critically examine the applicability of various models for the peaking of physical properties. It is shown that the models based on the concepts of phase coexistence, polarization rotation due to monoclinic structure, tricritical point and temperature dependent softening of…
An accurate estimate of the ferroelectric polarization in ferroelectric-dielectric stacks is important from a materials science perspective, and it is also crucial for the development of ferroelectric based electron devices. This paper revisits the theory and application of the PUND technique in Metal-Ferroelectric-Dielectric-Metal (MFDM) structures by using analytical derivations and numerical simulations. In an MFDM structure the results of the PUND technique may largely differ from the polarization actually switched in the stack, which in turn is different from the remnant polarization of t…
We have proposed the phenomenological description of dielectric hysteresis loops in ferroelectric semiconductors with charged defects and prevailing extrinsic conductivity. Exactly we have modified Landau-Ginsburg approach and shown that the macroscopic state of the aforementioned inhomogeneous system can be described by three coupled equations for three order parameters. Both the experimentally observed coercive field values well below the thermodynamic one and the various hysteresis loop deformations (constricted and double loops) have been obtained in the framework of our model. The obtaine…
Recently a new monoclinic phase in the PbZr(1-x)TixO3 ceramic system has been reported by Noheda et al. for the composition x= 0.48. In the present work, samples with Ti contents of x= 0.47 and 0.50, which are both tetragonal below their Curie points, have been investigated. In the sample with x= 0.50, the tetragonal phase was found to transform to a monoclinic phase at about 200 K as the temperature was lowered. The sample with x= 0.47 showed a complicated region of phase coexistence between 440-320 K, becoming rhombohedral at around 300 K. No further symmetry change was found down to 20 K. D…
We identify a first-order, isosymmetric transition between a ferrielectric (FiE) and ferroelectric (FE) state in $A$-site ordered LaScO$_{3}$/BiScO$_{3}$ and LaInO$_{3}$/BiInO$_{3}$ superlattices. Such a previously unreported ferroic transition is driven by the easy switching of cation displacements without changing the overall polarization direction or crystallographic symmetry. Epitaxial strains less than 2% are predicted to be sufficient to transverse the phase boundary, across which we capture a ~5X increase in electric polarization. In a fashion similar to classic Pb-based perovskite cera…
Ferroelectric domain structure evolution induced by an external electric field was investigated by means of nematic liquid crystal (NLC) method in two strontium-barium niobate single crystals of nominal composition: Sr_{0.70}Ba_{0.30}Nb_{2}O_{6} (SBN:70 - relaxor) and Sr_{0.26}Ba_{0.74}Nb_{2}O_{6} (SBN:26 - ferroelectric). Our results provide evidence that the broad phase transition and frequency dispersion that are exhibited in SBN:70 crystal have a strong link to the configuration of ferroelectric microdomains. The large leakage current revealed in SBN:26 may compensate internal charges acti…
Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramics have demonstrated excellent dielectric, ferroelectric and piezoelectric properties in comparison to lead-based materials. The synthesis of pure and crystalline BCZT nanopowders at low temperatures of 25, 80 and 160 C was reported previously by using a sol-gel method followed by a hydrothermal route. In this study, the structural, dielectric and ferroelectric properties of sintered BCZT ceramics at 1250 °C for 10h were investigated. XRD measurements revealed the presence of a single perovskite phase at room temperature with the coexistence of…
The origin of the functional properties of complex oxide superlattices can be resolved using time-resolved synchrotron x-ray diffraction into contributions from the component layers making up the repeating unit. The CaTiO3 layers of a CaTiO3/BaTiO3 superlattice have a piezoelectric response to an applied electric field, consistent with a large continuous polarization throughout the superlattice. The overall piezoelectric coefficient at large strains, 54 pm/V, agrees with first-principles predictions in which a tetragonal symmetry is imposed on the superlattice by the SrTiO3 substrate.
CuCrS2, a Heisenberg antiferromagnet with layered edge sharing triangular lattice, exhibits a spiral magnetic order. Dielectric (E) and polarization studies show magnetoelectric (ME) coupling at Neel temperature (T_N=38 K) where simultaneous dielectric and magnetic long range order occur. The compound shows a diffused ferroelectric (FE) transition and slow relaxation dynamics above T_N, indicative of relaxor FE behavior. Interestingly, memory effect and magnetic field induced rejuvenation are also observed in E, establishing cooperative glassy dynamics and ME coupling even above T_N. We discus…
New relaxor ferroelectric system has been synthesized. BLTN exhibits a smeared maximum of permittivity, characteristic of classic relaxor behaviour, with a peak shift from 185 K at 100 Hz to 300 K at 1 GHz. BNTN undergoes a first order ferroelectric phase transition at 389 K and BLNTN exhibits both a ferroelectric phase transition at 274 K and relaxor behaviour at higher temperatures.
The nanodomain pattern in ferroelectric/dielectric superlattices transforms to a uniform polarization state under above-bandgap optical excitation. X-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. The reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation.
A series of Pb-free ferroelectric materials Ba0.9Sr0.1Ti1-xSnxO3 (BSTS-x) with 0 < x < 0.15 was successfully prepared via solid-state reaction method. The effect of Sn substitution on the crystal structure, microstructure, dielectric behavior, ferroelectric and tunable features of BSTS-x ceramics were systematically investigated. Room temperature (RT) x-ray diffraction (XRD) analysis using the Rietveld refinement method reveals that all the synthesized BSTS-x ceramics were well crystallized into single perovskite structure. The results show a tetragonal phase for 0.00 < x < 0.02, which evolves…
Within the modified model of proton ordering of one-dimensional ferroelectric having hydrogen bonds of PbHPO$_4$-type, their thermodynamic and dynamic characteristics are studied and calculated taking into account the linear (by crystal deformations $\varepsilon_i$ ($i=1,3$) and $\varepsilon_4$) contributions into the energy of a proton system but without taking into account the tunneling in the two-particle cluster approximation. There has been obtained a good quantitative description of the temperature dependence of polarization, static dielectric permittivity, heat capacity and frequency de…
Ferroelectric perovskite oxides possess a large electrocaloric (EC) effect, but usually at high temperatures near the ferroelectric/paraelectric phase transition temperature, which limits their potential application as next-generation solid-state cooling devices. We use classical molecular dynamics to study the electric field induced phase transitions and EC effect in PMN-PT (PbMg1/3Nb2/3O3-PbTiO3). We find that the maximum EC strength of PMN-PT occurs within the morphotropic phase boundary (MPB) region at 300 K. The large adiabatic temperature change is caused by easy rotation of polarization…
