Polycrystalline Ferroelectric Ceramics Research Articles

Morphological evolution of plate-like B-site complex perovskite Pb(ZrxTi1-x)O3 microcrystals

Crystallographic texturing of polycrystalline ferroelectric ceramics is an effective approach to achieve single crystal-like properties via templated grain growth method (TGG). The TGG process strongly depends on the use of anisotropic single crystal templates. In this work, novel B-site complex Pb(ZrxTi1-x)O3(PZT) platelets are successfully fabricated via topochemical molten salt synthesis (TMSS). The Aurivillius phase of PbBi4Ti4O15(PBT) is obtained as precursor by molten salt method. Morphological evolution of Pb(ZrxTi1-x)O3 is investigated by varying the relative molar ratio of reactants and calcination temperature. However, the results of Raman spectroscopy show that the incorporation of Zr4+ content increases the instability of the perovskite structure. At 1100°C, it is possible to synthesize Pb(Zr0.2Ti0.8)O3 plate-like microcrystal templates with high aspect ratios and preferential orientations. These well-shaped microcrystals are suggested as a potential template material for the TGG fabrication of lead-based piezoelectric textured ceramics.

Configurational forces in ferroelectric structures analyzed by a macromechanical switching model

Polycrystalline ferroelectric ceramics are widely used in sensors, actuators, microelectromechanical systems, etc. If a ferroelectric structure possesses some defects like voids or inhomogeneities, its reliability is reduced, and undesired non-homogeneous local concentrations of the electromechanical fields occur. Under the applied external loading, a domain switching region evolves in the vicinity of defects, which is manifested as a reorientation of the remanent polarization vector. In the current work, the nonlinear electromechanical behavior of ferroelectric ceramics is computed by means of three-dimensional finite element analysis, using the phenomenological continuum mechanics model suggested by Landis (J. Mech. Phys. Solids 50(1):127–152, 2002. https://doi.org/10.1016/s0022-5096(01)00021-7) and numerically implemented by Stark (Int. J. Solids Struct. 80:359–367, 2015. https://doi.org/10.1016/j.ijsolstr.2015.09.004). This constitutive law is combined with user-developed elements in Abaqus commercial code for nonlinear coupled electromechanical analyses. By use of the numerical simulations, the evolution of all field variables, in particular of the polarization, is tracked. In a post-processing step, the configurational forces are computed, which express the thermodynamic driving forces acting on the defect. As a typical defect, we consider a circular void in the ferroelectric structure exposed to an alternating electric field. Additionally to the void, other inhomogeneities, namely, a strip of dissimilar material as well as dielectric and piezoelectric inclusions, are investigated. For all cases, the redistribution and evolution of the configurational forces are studied. Besides the essential findings and methodology achieved in this work, the developed software can serve as a basis for further investigations on the failure of composite smart structures and explicit crack modeling using fracture mechanical concepts.

Synthesis and dielectric properties of BCT ceramics co-substituted by Sm3+ and Fe3+ for capacitor applications

Polycrystalline ferroelectric ceramics with compositional formula Ba0.70−x Ca0.30SmxTi1−xFexO3 (BCSTF) with (0, 0.005, 0.010, 0.015 and 0.020) were prepared by solid state reaction route and sintered at 1325 °C for 4 h. Single perovskite phase with tetragonal structure was confirmed from X-ray diffraction (XRD) analysis. The dielectric constant ‘ε’ and tangent loss ‘tanδ’ were studied for all the samples as a function of frequency (100 Hz to 100 kHz) and temperature (30–200 °C). A very small low ‘tanδ’ (0.9% at 100 kHz) was observed. The high value of temperature coefficient of capacitance ‘Tcc’ (~10%) was observed for all the BCSTF samples. P-E hysteresis loops were recorded for sample with x = 0.020 at different temperature. Electrocaloric effect ‘ECE’ was investigated and the temperature change ‘ΔT’ was found to be 0.53 K at 35 kV/cm with a high value of electrocaloric coefficient (0.15 K m/MV). The results show that the prepared ceramics can be useful in applications such as capacitor, dielectric bolometers, electrocaloric applications.

Dielectric, ferroelectric, and piezoelectric properties of Gd-modified CaBi2Nb2O9 high Curie temperature ceramics

This paper reports the enhanced piezoelectric properties of gadolinium-modified Ca1−xGdxBi2Nb2O9 (CBN-100xGd, where x = 0–0.07) high Curie temperature polycrystalline ferroelectric ceramics. The crystal structure, microstructural morphology, and electrical properties of Gd-modified CBN ceramics are investigated in detail. The results reveal that the Gd-modified CBN ceramics have a pure two-layer Aurivillius-type structure, and exhibit plate-like grains. The resultant Gd-modified CBN ceramics exhibit better piezoelectric and electromechanical properties by comparison with unmodified CBN. The composition of CBN-3Gd exhibits the optimized piezoelectric performance with a high piezoelectric constant d33 value of 13 pC/N and a high Curie temperature Tc of 947 °C. The dc electrical resistivity is significantly enhanced, and that of the CBN-3Gd is 2.45 × 107 Ω cm at 500 °C and 1.53 × 106 Ω cm at 600 °C, which is larger by two orders of magnitude compared with that of unmodified CBN ceramics at the same temperature. Such good electrical properties suggest that the Gd-modified CBN ceramics are promising materials for high-temperature piezoelectric sensor applications.

Study on microstructural influence of graphene on synthesis of BaTiO3

Abstract A composite of polycrystalline Ferroelectric ceramics Barium titanate (BaTiO3) in perovskite (ABO3) structure with Graphene was prepared from BaCO3 and TiO2 mixture by sonicating, ball milled and followed by sintering at 1000 °C. Graphene of 0.04 mol added to BaTiO3 and sintered at 1000 °C to develop the crystalline and microstructural properties of composite. Composite sintered at 1000 °C temperature mostly shows pure barium titanate (BaTiO3) poly crystalline single phase material with presence of few secondary unwanted phases. X-ray diffraction (XRD) of the composite exhibits substantial effect of graphene on the crystal structure of barium titanate (BaTiO3). Micro Raman confirms the growth of BaTiO3.FESEM of Barium titanate (BaTiO3) with graphene (0.04 mol) almost shows change in crystal growth where grown of phases are clearly distinguished with porous free nature.

Synthesis, dielectric and ferroelectric properties of Sm3+ modified PZTFN ceramics

Polycrystalline ferroelectric ceramics with compositional formula Pb(1-1.5x)SmxZr0.588Ti0.392Fe0.01Nb0.01O3 ‘PSZTFN’, with x = 0.02 in steps of 0.005 were prepared by the conventional solid state route. The prepared samples were investigated for their structural, dielectric and ferroelectric properties. A direct relation was noticed between grain size and maximum dielectric constant ‘εmax’. Remnant polarization ‘Pr’ to saturation polarization ‘Ps’ ratio ‘Pr/Ps’ as recorded from the P-E hysteresis loops was found to be improved. The maximum value of the Pr/Ps ratio and Pr was 0.877 and 47.41 μC/cm2, respectively, for 2% of Sm3+ content. The maximum value of piezoelectric coefficient ‘d33’ is 356 for 2% of Sm3+ content. The enhancement in the Pr and remnant to polarization ratio suggests that the prepared materials are suitable for memory applications.

A phenomenological constitutive theory for polycrystalline ferroelectric ceramics based on orientation distribution functions

A phenomenological constitutive theory for the ferro-electro-elastic response of polycrystalline ceramics with tetragonal perovskite structure is proposed. The state of a material point is characterized by an intrinsic polarization vector, an infinitesimal deformation tensor, and an internal variable representing the orientation distribution of the ferroelectric domains at that point. A class of convex thermodynamic potentials in terms of these state variables is posited, and constitutive relations within the framework of generalized standard materials are then derived. The functional form of the dissipation is selected in such a way that it effects an order reduction of the constitutive description whereby the infinite-dimensional internal variable is reduced to finite-dimensional internal variables representing polarization and deformation due to ferroelectric switching, preserving at the same time the generalized standard structure of the theory. By way of example, a specific set of constitutive functions is considered. The resulting constitutive relations are able to emulate most essential features of ferroelectric and ferroelastic behavior with minimal computational cost and, furthermore, generate stable predictions in contrast to earlier phenomenological theories.

Structural, thermally stable dielectric, and energy storage properties of lead-free (1 − x)(Na0.50Bi0.50)TiO3 − xKSbO3 ceramics

Effect of substitution and external applied static electric field on the structural and dielectric properties for lead-free (1 − x)(Na0.50Bi0.50)TiO3 − xKSbO3 (0 ≤ x ≤ 0.06) polycrystalline ferroelectric ceramics, fabricated via a modified sol–gel method, were investigated. Structural analysis of synchrotron radiation X-ray diffraction data confirmed the rhombohedral R3c phase for all unpoled samples. After poling, the tetragonal P4bm phase appeared with the rhombohedral phase in all the substituted samples. In poled samples, the phase fraction of the rhombohedral phase suppressed from ~ 93 (for x = 0.03) to ~ 87% (for x = 0.06), while tetragonal phase fraction increased from ~ 7 to ~ 13% as a function of substitution. The high-temperature dielectric analysis confirmed the reduction in depolarization temperature with increasing substitution. Also lattice disorder creates a plateau type dielectric anomaly, which leads to thermally stable dielectric constant ~ 2970 ± 10% (200–390 °C) and ~ 2830 ± 10% (125–400 °C) for x = 0.03 and 0.06 samples, respectively. Ferroelectric measurements showed that ambient temperature ferroelectric properties are improved for x = 0.03 composition with an observed remnant polarization (2Pr ~ 53.4 µC/cm2) and coercive field (2Ec ~ 94.7 kV/cm) as compared to parent NBT compound (2Pr ~ 44.7 µC/cm2, 2Ec ~ 124.5 kV/cm). In addition, at high-temperature, antiferroelectric like ordering enhances the recoverable energy density ~ 0.73 J/cm3 (efficiency ~ 72.3%) for x = 0.06 samples as compared to parent NBT (recoverable energy density ~ 0.05 J/cm3, efficiency ~ 2.4%). These improvements in electrical properties were correlated with structural changes as a function of composition and temperature. Obtained properties suggest that substituted samples might be a suitable candidate for high-temperature stable capacitors (operating temperature > 200 °C), ferroelectric, and energy storage applications.

Investigation of dielectric and piezoelectric properties in aliovalent Eu3+‐modified Pb(Mg1/3Nb2/3)O3‐PbTiO3 ceramics

AbstractRare earth (Eu3+)‐modified Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) polycrystalline ferroelectric ceramics were fabricated by high‐temperature solid‐state sintering, the phase structure, dielectric and piezoelectric properties were investigated. Eu3+ addition was found to significantly improve dielectric and piezoelectric properties of PMN‐PT, where the optimized properties were achieved for the composition of 2.5 mol%Eu: 0.72PMN‐0.28PT, with the piezoelectric d33 = 1420 pC/N, dielectric εr = 12 200 and electromechanical k33 = 0.78, respectively. All these results indicate that the Eu3+‐doped PMN‐PT ceramics are promising candidates for high‐performance room‐temperature piezoelectric devices.

Crystal structure correlation of ferroelectric and dielectric properties of Nb doped PZT95/5

Pb(Zr0.95Ti0.05)1−xNbxO3 (x = 0.0, 0.02 and 0.025) polycrystalline ferroelectric (FE) ceramics were synthesized using conventional solid state method. The Rietveld refined X-ray diffraction pattern show all the compositions crystallize in the rhombohedral phase with R3c space group. The scanning electron microscopy result depicts the decrease in grain size with increase in niobium (Nb) doping. The temperature dependent dielectric permittivity shows the Nb doping increases the Curie temperature (Tc) and decreases the dielectric constant (er) at Tc. FE analysis shows doping of Nb increases the remnant polarization (Pr) and decreases the coercive field (Ec).

Tailored dielectric and magnetic properties of composite electroceramics with ferroelectric and ferrimagnetic components

High-frequency coaxial waveguide measurements are used to evaluate composition- and frequency-dependent complex permittivities and permeabilities of polycrystalline ferroelectric and ferrimagnetic ceramics. Material dielectric and magnetic property measurements were performed on ferroelectric barium titanate (BaTiO3) and ferrimagnetic yttrium iron garnet (YIG), with the upper measurement frequency bound below gyromagnetic resonance of YIG. These polycrystalline materials were chosen because of their widespread use in voltage- and magnetic field-tunable devices. Wideband frequency material measurements were used to predict dielectric and magnetic properties of various two-phase composite media incorporating BaTiO3 and YIG. Two effective medium theories were used: an asymmetric, modified Maxwell-Garnett type and a symmetric Bruggeman model. The Bruggeman effective medium model is extended to include three-phases. The three-phase Bruggeman predictive model is employed when controlled porosity is introduced into the composite and when two component phases are combined with polytetrafluoroethylene.

Fluctuations of Current in Polycrystalline Ferroelectric Ceramics

Experimental data on fluctuations of leakage currents over time in samples of polycrystalline ferroelectric ceramics (SBPZT-1, ceramics based on sodium bismuth lead zirconate–titanate) upon the application of a constant electric field are considered. Variations in the type of leakage current dependence on time with an increase in electric field strength on samples with different values of the loss-angle tangent are determined. Exponential decay is accompanied by random jumps, i.e., variations in the values of the leakage current.

Effect of co-substitution of Sm3+ and Fe3+ ions on structural and dielectric properties of BaTiO3 ceramics

The material series of polycrystalline ferroelectric ceramics with compositional formula (Ba1-xSmx)(Ti1-xFex)O3 (with 0 ≥ x ≥ 0.01 in steps of 0.0025) was prepared by solid-state reaction method. The samples were sintered at 1300 °C (for x = 0) and 1325 °C for (x > 0). The sintered samples were subjected to X-ray diffraction (XRD) analysis and found to have single phase with tetragonal perovskite structure. Average grain size decreases with increase in substituent content. Dielectric behavior was studied as a function of temperature at different frequencies (1, 10,100,1000 kHz). The lattice constant ‘c’, tetragonality‘c/a ratio’ and Curie temperature ‘Tc’ was found to decrease with increase in the substituent content whereas the room temperature dielectric constant increases with substituent content. Large value of temperature coefficient of capacitance ‘Tcc’> 10%/°C near Tc was observed for all the samples.

Multiscale simulations of defect dipole–enhanced electromechanical coupling at dilute defect concentrations

The role of defects in solids of mixed ionic-covalent bonds such as ferroelectric oxides is complex. Current understanding of defects on ferroelectric properties at the single-defect level remains mostly at the empirical level, and the detailed atomistic mechanisms for many defect-mediated polarization-switching processes have not been convincingly revealed quantum mechanically. We simulate the polarization–electric field (P–E) and strain–electric field (ε–E) hysteresis loops for BaTiO3 in the presence of generic defect dipoles with large-scale molecular dynamics and provide a detailed atomistic picture of the defect dipole–enhanced electromechanical coupling. We develop a general first-principles-based atomistic model, enabling a quantitative understanding of the relationship between macroscopic ferroelectric properties and dipolar impurities of different orientations, concentrations, and dipole moments. We find that the collective orientation of dipolar defects relative to the external field is the key microscopic structure feature that strongly affects materials hardening/softening and electromechanical coupling. We show that a small concentration (≈0.1 at. %) of defect dipoles dramatically improves electromechanical responses. This offers the opportunity to improve the performance of inexpensive polycrystalline ferroelectric ceramics through defect dipole engineering for a range of applications including piezoelectric sensors, actuators, and transducers.

Enhanced electrocaloric effect in lead-free 0.9(K0.5Na0.5) NbO3 [sbnd]0.1Sr(Sc0.5Nb0.5)O3 ferroelectric nanocrystalline ceramics

The environmentally friendly and low-cost ferroelectric refrigeration based on the electrocaloric effect (ECE) has attracted considerable attention to replace the conventional vapor compression cooling technology. The ECE has been experimentally demonstrated in lead-free 0.9(K0.5Na0.5)NbO30.1Sr(Sc0.5Nb0.5)O3 (KNN-0.1SSN) polycrystalline ferroelectric ceramics using an indirect thermodynamic method. A large electrocaloric effect (adiabatic temperature change) of 0.28 K was observed near the transition temperature of 357 K for electric field 25 kV/cm, and that corresponds to an electrocaloric responsivity of ΔT/ΔE = 0.27 × 10−7 K mV−1, significantly larger than the pristine KNN based ceramics. A concurrent increment in specific entropy change of the material was also observed. The results indicate that ferroelectric KNN-0.1SSN materials possess a huge potential for electrocaloric refrigeration as a micro-cooler for electronic devices.

Predicting the effective response of bulk polycrystalline ferroelectric ceramics via improved spectral phase field methods

Understanding the electromechanical response of bulk polycrystalline ferroelectric ceramics requires scale-bridging approaches. Recent advances in fast numerical methods to compute the homogenized mechanical response of materials with heterogeneous microstructure have enabled the solution of hitherto intractable systems. In particular, the use of a Fourier-based spectral method as opposed to the traditional finite element method has gained significant interest in the homogenization of periodic microstructures. Here, we solve the periodic, electro-mechanically-coupled boundary value problem at the mesoscale of polycrystalline ferroelectrics in order to extract the effective response of barium titanate (BaTiO3) and lead zirconate titanate (PZT) under applied electric fields. Results include the effective electric hysteresis and the associated butterfly curve of strain vs. electric field for mean stress-free electric loading. Computational predictions of the 3D polycrystalline response show convincing agreement with our experimental electric cycling and strain hysteresis data for PZT-5A. In addition to microstructure-dependent effective physics, we also show how finite-difference-based approximations in the spectral solution scheme significantly reduce instability and ringing phenomena associated with spectral techniques and lead to spatial convergence with h-refinement, which have been major challenges when modeling high-contrast systems such as polycrystals.

An effective constitutive model for polycrystalline ferroelectric ceramics: Theoretical framework and numerical examples

We present an efficient, physics-based constitutive model for bulk polycrystalline ferroelectric ceramics, which links domain switching mechanisms and phase transitions at the microscale to the observed electro-thermo-mechanically coupled material response at the macroscale. In particular, a convexified energy density is formulated based on domain volume fractions and extended to polycrystals via the common Taylor assumption of uniform strains (alternative descriptions are discussed as well). The chosen kinetic relations admit to account for differences in 90°- and 180°-domain wall motion and rate effects. The model is applied to tetragonal barium titanate (BaTiO3) and we present results for both material point calculations and finite element simulations, which demonstrate good qualitative agreement with experiments. We deliberately target bulk polycrystalline ferroelectrics in contrast to thin films that have been studied extensively.

Influence of internal electric and elastic fields on characteristics of heterogeneous ferroelectric materials

Dielectric properties of polycrystalline ferroelectric ceramics and ferroelectrics with compensated impurities were investigated. Electric fields at the boundaries between crystallites and the fields created by a random distribution of impurities were calculated. It was shown, that the influence of these fields leads to an increase in the effective dielectric constant and to a displacement of the phase transition temperature in these ferroelectrics to lower temperatures. These effects are associated with an asymmetric nonlinear dependence of the thermodynamic potential near to the equilibrium value of spontaneous polarization vector. The asymmetry of this dependence in the random electric and elastic fields with a zero mean value reduces the length of the spontaneous polarization vector. The polarization reduced by the indicated fields lies in a region with less curvature of the thermodynamic potential that effectively means growth the value of dielectric constant of the studied system.

Effect of Reoriented Nanodomains on Crystal Structure and Piezoelectric Properties of Polycrystalline Ferroelectric Ceramics

It has been widely accepted that electric fields induce a reversible structural phase transition and thus yield giant piezoelectric responses in ferroelectric ceramics. Based on detailed measurements of polycrystalline (Li0.5Nd0.5)2+-modified 0.95Bi0.5Na0.5TiO3-0.05BaTiO3 ceramics, we demonstrate in this study that coherent diffraction from nanodomains in ferroelectric ceramics masks the real crystal structure. The observed electric-field-induced phase transformation behavior is a consequence of relaxor-to-ferroelectric transformation caused by changes in the coherence length of the nanodomains. A driving mechanism of the structure–property relationship in which high piezoelectric properties originate from correlated ordering of nanodomains during poling is proposed.

Broadband control of the viscoelasticity of ferroelectrics via domain switching

We show that the viscoelastic properties of polycrystalline ferroelectric ceramics can be significantly altered over a wide range of mechanical frequencies when domain switching is controlled by cyclic electric fields. The dynamic stiffness of lead zirconate titanate is shown to vary by more than 30%, while damping increases by an order of magnitude. Experimental results are interpreted by the aid of a continuum-mechanics model that captures the nonlinear electro-mechanically coupled material response for the full electric hysteresis.