Remnant Polarization Values Research Articles

Next-generation hybrid nanogenerators using giant piezoelectric lead-free KNNS composites for sustainable self-powered electronics

This study presents a flexible hybrid nanogenerator that utilizes lead-free KNNS-BF-xBNZ materials integrated with polydimethylsiloxane (PDMS) to enhance energy harvesting performance. The findings demonstrate that by combining piezoelectric and triboelectric effects, the energy conversion efficiency of the nanogenerator is significantly improved, resulting in high output voltage and current, suitable for real-world applications. Specifically, the optimal composition of KNNS-BF-xBNZ ceramics, with x = 0.03 mol.%, yields superior piezoelectric, ferroelectric, and dielectric properties, with remnant polarization (Pr), spontaneous polarization (Ps), and piezoelectric coefficient (d33) values reaching 18.8 μmC/cm², 30.3 μmC/cm², and 358 pC/N, respectively. In the hybrid device, incorporating 15 wt% of KNNS-BF-3BNZ into PDMS resulted in the highest open-circuit voltage (VOC) of 107 V and short-circuit current (ISC) of 4.68 μA. The developed hybrid nanogenerator effectively charges capacitors for energy storage, powers LEDs, and drives small electronic devices, such as watches, showcasing its potential for practical energy harvesting applications. The findings suggest that the integration of KNNS-BF-3BNZ with PDMS provides an efficient and scalable pathway for fabricating high-performance nanogenerators, paving the way for advancements in self-powered devices and sustainable energy solutions.

Improved lateral figure-of-merit of heteroepitaxial α-Ga2O3 power MOSFET using ferroelectric AlScN gate stack

In this Letter, we demonstrate heteroepitaxial α-Ga2O3 MOSFETs using an aluminum scandium nitride (AlScN) ferroelectric gate stack. Owing to ferroelectric effects, α-Ga2O3 MOSFETs with the AlScN/HfO2 gate stack (FGFET) exhibited enhanced electrical performance compared with a HfO2 gate dielectric (IGFET) for variable gate–drain lengths (10, 15, 20 μm). A remnant polarization value of the AlScN deposited on a HfO2 layer was measured to be about 30 μC/cm2. The subthreshold swing (SS) and field-effect mobility (μFE) of IGFET was extracted at 1814 mV/dec and 13.9 cm2/V s, respectively. However, the FGFET exhibits a reduced SS of 552 mV/dec with enhanced μFE of 42.7 cm2/V s owing to the negative capacitance of the ferroelectric AlScN. Furthermore, a lateral figure-of-merit of 17.8 MW/cm2 was achieved for the FGFET, far surpassing the 8.3 MW/cm2 of the IGFET. The proposed ferroelectric AlScN/HfO2 stack can be a promising gate structure for improving both transfer and breakdown characteristics in heteroepitaxial α-Ga2O3 power devices.

Structural refinement, dielectric and ferroelectric properties of Cr modified Ba0·90Sr0·10TiO3 ceramics

In this study, we investigated the impact of Chromium substitution on the structural, dielectric and ferroelectric characteristics of Ba0·90Sr0·10Ti1-3x/4CrxO3 (x = 0, 0.005, 0.010, 0.015 and 0.020) ceramics fabricated by solid state reaction method. Rietveld refinement of X-ray diffraction pattern confirmed tetragonal perovskite structure for all the samples. Based on the crystal structure and the lattice parameter obtained through XRD measurement, the Madelung energy of each sample was computed. SEM images revealed a reduction in grain size with rising Cr concentration. TEM, HRTEM, SAED and EDS analysis was carried out for BST-Cr3 sample. Diffused rings observed in Selective Area Electron Diffraction (SAED) patterns indicate the crystallinity of the sample. EDS analysis indicated the presence of Ba, Sr, Ti, O and Cr elements. In the temperature range of 30 °C–150 °C, dielectric measurements (dielectric constant ‘ε’ and tangent loss ‘tanδ’) have been made at different frequencies (1, 10, 50, 100 and 1000 kHz). The samples displayed a diffused phase transition, with noticeable reduction in Curie temperature ‘Tc’ and tangent loss ‘tanδ’ with the substitution of Cr. Polarization versus electric field loops were recorded at different electric fields (5, 10, 15, 20 and 25 kV/cm) and improved values of remnant polarization ‘Pr’ and coercive field ‘Ec’ were observed. A lower Ec value facilitates easier domain movement within the unit cell, leading to enhanced ferroelectric properties. Temperature dependent P-E loops indicated that as the temperature increased, the material became softer accompanied by simultaneous reduction in Pr and Ec values.

Enhanced magnetoelectric properties of the composite films of Bi0.5Na0.5Ti0.98Fe0.02O3-δ-NiFe1.98Nd0.02O4 with different deposition sequences

The films of Bi0.5Na0.5Ti1-xFexO3-δ and NiFe2-xNdxO4 were deposited via spin-coating method. The results indicate that the film of Bi0.5Na0.5Ti0.98Fe0.02O3-δ possesses good ferroelectric performance with remnant polarization as high as 25.2 µC·cm−2 and the film of NiFe1.98Nd0.02O4 possesses a maximal saturation magnetization (282.4 emu·cm−3). The composite films of Bi0.5Na0.5Ti0.98Fe0.02O3-δ-NiFe1.98Nd0.02O4 with different deposition sequences were also prepared. In contrast to single-phase films, magnetoelectric composite films exhibit smaller remnant polarization and saturation magnetization. The film of NiFe1.98Nd0.02O4/Bi0.5Na0.5Ti0.98Fe0.02O3-δ (NB) possesses greater values of remnant polarization, saturation magnetization and magnetoelectric coupling coefficient than those for the composite film of Bi0.5Na0.5Ti0.98Fe0.02O3-δ/NiFe1.98Nd0.02O4 (BN). The composite film of BN exhibits greater magnetoelectric coupling coefficients as high as 169.7 mV·cm−1·Oe−1.

Evidence of self-biased magnetoelectric coupling in eco-friendly (Na0.41K0.09Bi0.5TiO3-Ba0.85Ca0.15Zr0.1Ti0.9O3)-(CoFe2O4) particulate composites

The magnetoelectric (ME) properties of eco-friendly 1-x(0.94Na0.41K0.09Bi0.5TiO3-0.06Ba0.85Ca0.15Zr0.1Ti0.9O3)-x (CoFe2O4) (NKBCZT-CFO) with x = 0, 0.1, 0.2, 0.3 and 0.4 particulate composites were investigated. The X-ray diffraction studies provided evidence for the simultaneous existence of constituent phases (ferroelectric and ferromagnetic) in the composite. The structural and surface morphology analysis of the composite affirmed the homogeneous and densely packed distribution of CFO grains within the NKBCZT matrix. The composite's multiferroic behavior at room temperature was confirmed through the characterization of P vs E and M vs H hysteresis loops. The observed values of remnant polarization (Pr) and coercive field (Ec) are 26.7 μC/cm2 and 35.5 kV/cm, respectively, for 10 mol% of CFO. The increase in CFO content resulted in a decrease in the ferroelectric properties, possibly due to the conductive behaviour exhibited by CFO, and correlated with leakage current measurement. For the composite containing 40 mol% of CFO, the estimated values of remanent (Mr), saturation (Ms) magnetization, coercive field (Hc), and magnetic moment (µB) are 2.35 emu/g, 21.85 emu/g, 104.2 Oe, and 0.86 µB, respectively. The non-Debye type dielectric relaxation processes have been observed in the composites, and the electron hopping mechanism resulted in a higher dielectric constant (εʹ). Enhancement in relaxor nature had been observed through Vogel-Fulcher analysis with CFO content. The evidence of ME coupling was revealed through the direct ME voltage coefficient (αME) and magnetocapacitance (MC) measurement. The observed maximum value of MC measured at 1 kHz for the 20 mol% CFO is ∼5.6 %. Self-biased ME coupling (non-zero αME at HDC = 0 Oe) was observed in 20 and 30 mol% of CFO composite. The highest measured value of αME for 20 and 30 mol% CFO is 3.63 mV/cm.Oe and 4.09 mV/cm.Oe at HDC = 0 Oe respectively. The strong ME interaction and significant value of self-biased ME αME suggest that these composites can be explored for magnetic sensor and ME memory device applications.

Moderation of [Bi3+/Na1+] molar ratio for enhancement of dielectric and energy storage properties of NaNbO3 ceramics

Lead-free (Na1−3xBix)(Nb0.75Ti0.25)O3 (x = 0.0, 0.05, 0.1, 0.125 and 0.15) (NN-BT) ceramics were synthesized using solid-state reaction technique. The effect of Bi3+ into the crystal structure, dielectric, ferroelectric and energy storage properties of NNT ceramics were investigated. Pure NNT shows present perovskite structure with orthorhombic crystal structure at x ≤ 0.125, while Na3NbO8-NaNbO3 composite phase has been detected at x = 0.15. The tolerance factor (τ) decreased from 0.97 (x = 0.0) to 0.82 (0.15) which signified the composition deviated from perovskite structure at 0.15. Significant enhancement of dielectric constant at room temperature has been achieved by increasing Bi-content and the maximum value (∼1500) obtained at 0.1. The largest value of maximum polarization (Pmax) and smallest value of remnant polarization (Pr) were achieved at x = 0.1 due to orthorhombic NaNbO3 and rhombohedral (Na0.5Bi0.5)TiO3 coexistence phases. The substitution of monovalent (Na1+) by trivalent (Bi3+) lead to create sodium vacancies into the A-sites of NNT lattice subsequently increased the cations disorder and charge misfit. The maximum recoverable energy storage density (Wrec = 17.5 J cm−3) and energy storage efficiency (η = 80%) were achieved at x = 0.1, E ∼ 700 kV cm−1. Partially, (NNTB0.1) exhibit an outstanding stability of energy storage properties in terms of temperature range (25 to 150 °C) and frequency stability (2–20Hz). The present results imply the moderation ratio of Bi/Na plays an important role for enhancement of energy storage properties of NaNbO3 anti-ferroelectric ceramics.

Structural phase coexistence enhances the energy storage density of (Bi0.5Na0.5)0.8Ba0.2Ti1-ySnyO3 lead-free ceramics

In the present study, BaSnO3 was introduced into polycrystalline NBT-BT ferroelectric ceramics and conducted a comprehensive investigation into the structural, dielectric, ferroelectric, and energy storage characteristics of the (Bi0.5Na0.5)0.8Ba0.2Ti1-ySnyO3 (BNBTS) ceramics. The coexistence of structural phases P4mm and Amm2 was observed through Rietveld refinement and also confirmed by Raman analysis. The formation energy decreases with an increase in substitution concentration favouring the formation of the orthorhombic phase. The SEM analysis revealed a denser microstructure characterised by smaller grain sizes, which favourably enhances energy storage density. Furthermore, Raman spectroscopic analysis unveiled a softening of Ti–O bonds, indicating the emergence of macroscopic relaxor behaviour. Dielectric studies provided evidence of a transition from ferroelectric to relaxor behaviour, an observation further confirmed by P-E loop measurements. This transition can be linked to the partial substitution of Sn4+ ions for Ti4+ ions, disrupting the ferroelectric long-range order within the matrix phase. Notably, the polarization-electric field (P-E) loop of BNBTS2 ceramics exhibited a substantial value of polarization (Ps) 30 μC/cm2 with a reduced value of remnant polarization (Pr) 2.29 μC/cm2. These characteristics contributed to the achievement of higher energy recovery (Wrec) and lower energy loss (Wloss) values, measuring 1.184 J/cm3 and 0.142 J/cm3, respectively, with a notable efficiency of 88.8%. Consequently, the system of ternary ceramics demonstrates promise as a potential option for energy storage ceramics among NBT-BT-based materials.

Structure, ferroelectric, and enhanced fatigue properties of sol–gel-processed new Bi-based perovskite thin films of Bi(Cu1/2Ti1/2)O3–PbTiO3

Bi-based perovskite ferroelectric thin films have wide applications in electronic devices due to their excellent ferroelectric properties. New Bi-based perovskite thin films Bi(Cu1/2Ti1/2)O3–PbTiO3 (BCT–PT) are deposited on Pt(111)/Ti/SiO2/Si substrates in the present study by the traditional sol–gel method. Their structures and related ferroelectric and fatigue characteristics are studied in-depth. The BCT–PT thin films exhibit good crystallization within the phase-pure perovskite structure, besides, they have a predominant (100) orientation together with a dense and homogeneous microstructure. The remnant polarization (2P r) values at 30 μC/cm2 and 16 μC/cm2 are observed in 0.1BCT–0.9PT and 0.2BCT–0.8PT thin films, respectively. More intriguingly, although the polarization values are not so high, 0.2BCT–0.8PT thin films show outstanding polarization fatigue properties, with a high switchable polarization of 93.6% of the starting values after 108 cycles, indicating promising applications in ferroelectric memories.

Unveiling the role of vanadium doping in modulating morphological and electrical properties of piezoelectric Na0.46K0.46Li0.08NbO3 ceramics for energy harvesting

We report the enhancement of ferro/piezo-electric properties of lead-free alkali based perovskite Na0.46K0.46Li0.08NbO3 (NKLN) by vanadium doping (NKLNV) for high performing piezoelectric devices. Lead-free NKLN and NKLNV ceramics are synthesized via solid state reaction route as a substitute to the lead-based ceramic for the applications in sensors, transducers, and other electronic devices. The structural phase of synthesized ceramics is found to be pure perovskite as observed from powder X-ray diffraction. In dielectric studies, Curie temperature is found to be around 450 °C for both the samples. SEM images revealed the formation of homogeneous microstructure with well-defined grains. Dense polycrystalline ceramics having grain size of about 5 μm are obtained as a result of sintering at optimised temperature of 1050 °C. The micrographs showed that the grain size begins to evolve with reduced porosity in vanadium doped NKLN. Vicker's microhardness indentation test is performed for different loads at dwell time of 30 s, in which it was observed that the V-doping has enhanced the hardness. In ferroelectric studies, NKLNV shows higher value of remnant polarization as compared to NKLN as observed in P-E hysteresis loop. Fine microstructure and larger grain size felicitated the movement and reorientation of dipoles which resulted in enhanced piezoelectric coefficient for vanadium substituted NKLN ceramics. Flexible energy harvesters were fabricated by making a composite with PDMS, and then coating a thick film over ITO/PET sheet. NKLNV-based flexible device showed an improvement in open-circuit output voltage of 13.8 V under gentle finger tapping. NKLNV ceramics are a viable lead-free alternative for dielectric, piezoelectric, and ferroelectric applications.

HfO2-ZrO2 Ferroelectric Capacitors with Superlattice Structure: Improving Fatigue Stability, Fatigue Recovery, and Switching Speed.

HfO2-ZrO2 ferroelectric films have recently gained considerable attention from integrated circuit researchers due to their excellent ferroelectric properties over a wide doping range and low deposition temperature. In this work, different HfO2-ZrO2 superlattice (SL) FE films with varying periodicity of HfO2 (5 cycles)-ZrO2 (5 cycles) (SL5), HfO2 (10 cycles)-ZrO2 (10 cycles) (SL10), and HfO2 (15 cycles)-ZrO2 (15 cycles) (SL15) were studied systematically. The HfZrOx (HZO) alloy was used as a comparison device. The SL5 film demonstrated improved ferroelectric properties compared to the HZO film, with the 2 times remnant polarization (2Pr) values increasing from 41.4 to 48.6 μC/cm2 at an applied voltage of 3 V/10 kHz. Furthermore, the first-order reversal curve diagrams of different SL and HZO capacitors at different states (initial, wake-up, fatigue, and recovery) were measured. The SL capacitors were found to effectively suppress the diffusion of defects during P-V cycling, resulting in improved fatigue stability characteristics and fatigue recovery capability compared to the HZO capacitor. Moreover, an improved switching speed of the SL films compared to the HZO capacitor was concluded based on the inhomogeneous field mechanism (IFM) model. These results indicate that the SL structure has a high potential in future high-speed ferroelectric memory applications with excellent stability and recovery capability.

A comparative study by mechanical activation and conventional processes of BaTi0.95W0.05O3 ferroelectric ceramic

BaTi0.95W0.05O3 is synthesized by both mechanical activation process and conventional solid-state reaction technique for comparative study. The prepared sample is characterized by XRD and SEM. There is proper formation of perovskite structure in BTW from both of the methods confirmed by XRD. Scanning electron microscopy (SEM) depicts that the micro-grains obtained by the mechanical activation method had comparatively fine structure compared to that of the conventional solid-state process. The mechanically activated samples display enhanced electrical properties showing a high value of the dielectric constant and a low value of the dielectric loss. The remnant polarization (Pr) value and d33 values were also high in samples synthesized by the mechanical method.

Voigt Profile is Suitable for Impedance Spectroscopic Analysis of BLSF Ceramics

Abstract: In our earlier studies, samarium-modified bismuth layer-structured ferroelectrics (BLSF), namely SmxBi3-x TiNbO9 (SBTN); (x=0, 0.2, 0.4, 0.6. 0.8, and 1.0), prepared by solid-state reaction method, have shown broad dielectric relaxations. Among all the compositions, Bi2.6Sm0.4TiNbO9 (BST-0.4) has shown a lower tolerance factor, high remnant polarization (Pr) value, and low stretching factor. In addition, the compound has shown interesting broad dielectric relaxation and non-Debye nature. The specific reasons for the broad relaxation remain unclear. To gain more insights, we synthesized multi rare earth ion substituted compounds, namely, Bi2.6La0.2Sm0.2TiNbO9 (sample A) and Bi2.6La0.2Gd0.2TiNbO9 (sample B), using the conventional solid-state reaction method. A single impedance spectroscopic approach alone may not be sufficient to explain the asymmetric or non-Debye behavior, therefore Lorentzian, Gaussian, and Voigt fitting were adopted in the present investigation. From the analysis, the Voigt profile (Vf and Vʹf) is found to be a valuable alternative tool to understand the broad impedance non-Debye relaxations. Finally, results were corroborated by dc-conductivity data. Keywords: BLSF, Modulus spectroscopy, Relaxation, Defect-mechanism, Gaussian, Lorentz and Voigt fitting, Dc conductivity.

Influence of the Annealing Environment on the Structure and Ferroelectric Properties of Lead Titanate Thin Films

Lead titanate thin films of pyrochlore phase were deposited using layer-by-layer reactive magnetron sputtering on a heated platinized silicon substrate. It was found that the pyrochlore phase transition to the perovskite phase was initiated at 700 °C, and the properties of the PbTiO3 films could be controlled by changing the annealing environment. The thin films annealed in air and oxygen environments (1.33 Pa) have a tetragonal structure. The highest values of remnant polarization and the coercive field were 38 μC/cm2 and 130 kV/cm, respectively, but the largest dielectric loss was determined for the films annealed in air. The remnant polarization, coercive field and dielectric loss were reduced when the annealing of films was performed using oxygen gas at 1.33 Pa pressure. The films annealed in vacuum showed a rhombohedral (and ferroelectric) structure with the lowest remnant polarization and coercive field values. Such a structure was not observed for lead titanate at room temperature. It was observed that the surface morphology strongly depended on the reaction rate, which was influenced by the oxygen concentration in the environment.

Exploration of temperature driven conduction process and ferroelectric properties of Mn doped GdCrO3

This work delivers the research findings of the temperature dependent DC resistivity, AC impedance and ferroelectric polarization of GdCr1−xMnxO3 (x = 0 and 0.3). Mixed valence states of Cr (Cr3+ and Cr4+) are explored using the x-ray photoelectron spectroscopy analysis. The exponential decay of DC resistivity on escalating the temperature advocates the semiconducting-like nature for the probed samples. The DC resistivity data of these samples fit well into small-polaron hopping and variable range hopping models. The impedance attributes of these samples were scrutinized over a broad spectrum of temperatures at selected frequencies. The values of the real and imaginary parts of impedance unveil substantial reduction on raising the temperature, thereby signifying the increase in conductivity of the samples. Pristine sample displays an electrical relaxation peak at 65 °C, which translates towards the lower temperature at higher frequencies. Further, the semicircular behavior of Nyquist plots at higher temperatures indicates the reduction of the charge transfer resistance. The equivalent circuits of Nyquist plots are generated using Z-view software. From these plots, it is perceived that grain boundary resistance upsurges while the grain resistance and capacitance drops upon doping. The ferroelectric measurements reveal that the coercive field (Ec) values decrease whereas the values of maximum polarization (Pm), remnant polarization (Pr) and energy storage increase in 30% doped GdCrO3. These observations establish that electrical and ferroelectric properties of GdCrO3 system can be tuned with appropriate Mn doping.

Investigations on structural, morphological, dielectric, and ferroelectric properties of BiFeO3/BiMnO3 composite ceramics prepared via sol–gel synthesis route

In this work, we report the preparation of BiFeO3/BiMnO3 (BFO/BMO) composite material, via the chemical substitution method, by adopting the sol–gel method. The X-ray diffraction studies confirmed the formation of two distinct phases in the prepared sample. Field emission scanning electron microscopic images revealed the two different morphologies, and the compositional studies verified the presence of the respective elements in these different grains. The dielectric constant value almost doubled in the composite sample than the single-phase BFO sample. The dielectric constant values at a frequency of 105 Hz were found to be 46 and 73 for the BFO and BFO/BMO samples, respectively. The remnant polarization value was found to reduce from 8.3 µC/cm2 (for BFO) to 0.3 µC/cm2 for biphasic BFO/BMO samples.

Study on the properties of sodium bismuth titanate coating prepared by supersonic plasma spraying

In order to realize the preparation of environmentally friendly piezoelectric ceramic coatings on the surface of metallic materials, sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT) ceramic coatings were prepared by supersonic plasma spraying. The surface morphology, cross-sectional morphology, phase structure, and elemental valence variations of the BNT coating were examined, as well as the dielectric and ferroelectric properties of the BNT coating. The results show that the coating has a good quality and a single perovskite structure. The dielectric constant was stable at about 425 and the dielectric loss was stable at about 0.06 when the test frequency reached 200 kHz. The coating exhibits good hysteresis lines under different applied electric fields. When the applied electric field was 40 kV/cm, the remnant polarization value of the prepared coating was 11.47 µC/cm2. It can be seen that the BNT piezoelectric coating prepared by supersonic plasma spraying has good ferroelectric and dielectric properties, which lays a solid foundation for in-situ monitoring of environmentally friendly lead-free BNT piezoelectric coating.

Properties of PBZTS Ferroelectric Ceramics Obtained Using Spark Plasma Sintering.

In this paper, spark plasma sintering was used to obtain and investigate (Pb0.97Ba0.03)(Zr0.98Ti0.02)1-xSnxO3 (PBZTS) ceramic materials for x = 0, 0.02, 0.04, 0.06, and 0.08. Crystal structure, microstructure, dielectric and ferroelectric properties, and electrical conductivity tests of a series of samples were carried out. The SPS sintering method ensures favorable dielectric and ferroelectric properties of PBZTS ceramic materials. X-ray studies have shown that the material has a perovskite structure. The samples have a densely packed material structure with properly crystallized grains. The fine-grained microstructure of the PZBZTS material with high grain homogeneity allows the application of higher electric fields. Ceramic samples obtained by the SPS method have higher density values than samples obtained by the classical method (FS). The permittivity at room temperature is in the range of 245-282, while at the phase transition temperature is in the range of 10,259-12,221. At room temperature, dielectric loss factor values range from 0.006 to 0.036. The hysteresis loops of PBZTS ceramics have a shape typical for ferroelectric hard materials, and the remnant polarization values range from 0.32 to 0.39 µC/cm2. The activation energy Ea values of the PBZTS samples result mainly from the presence of oxygen vacancies. The PZT material doped with Ba and Sn and sintered via the SPS method has favorable physical parameters for applications in modern devices such as actuators or pulse capacitors.

Effect of preparation methodologies on the electrical properties of lead-free 0.985(K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3-0.015(Bi0.5Na0.5)ZrO3 piezoceramics

Two methods of preparation namely, one-step solid state method and two-step solid state method, were used to synthesize composite 0.985(K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3-0.015(Bi0.5Na0.5)ZrO3 (0.985KNNLS-0.015BNZ) piezoceramics. In one-step method, all the raw materials were mixed in their stoichiometric ratios and then calcined to yield the desired composite. In two-step method, calcined samples of (K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3 (KNNLS) and (Bi0.5Na0.5)ZrO3 (BNZ) were initially prepared following the above procedure, these calcined powders were mixed according to the required compositional ratios and then again calcined to get the final composite. The calcined powders were again high-energy ball-milled in isopropanol medium at the speed of 250 rpm for 10 h. The powders were pressed into pellets and sintered at 1060 °C for 2 h. According to XRD analysis and Raman spectra, both the resulting ceramic samples show pure perovskite structure. The study reveals the great influence of the preparation technique on the microstructural, electrical and pieozoelectric properties of the resulting ceramics. Significantly higher value of Curie temperature Tc = 331 °C was observed for ceramics prepared via two-step method as compared to Tc = 197 °C for ceramics synthesized via one-step method. Modified Curie Weiss law and Vogel-fulcher relation suggest that two-step approach induces more relaxor character in the sample. The values of piezoelectric coefficient (d33 = 367 pC/N), remnant polarization (Pr = 13µC/cm2) and dielectric permittivity (εrt = 2166) corresponding to the two-step method far exceed those (d33 = 253 pC/N, Pr = 6.65 µC/cm2, εrt =1428) of the one-step method. These observed results are discussed in this paper.

Structural, electrical and electron emission property studies of high dielectric constant (Pb0.88La0.12)(Zr0.65Ti0.35)O3 ceramics for ferroelectric cathode applications

Ferroelectric materials with high dielectric constant produce high electron emission and the life span of ferroelectric cathodes might be potentially increased if their piezoelectric charge coefficient can be made negligible. For achieving these properties, two different methods were employed to synthesize (Pb0.88La0.12)(Zr0.65Ti0.35)O3 (PLZT12/65/35) ceramics viz., the conventional method (mortar and pestle) followed by uniaxial pressing and the high energy, mechanical activation method (abbreviated to MA, hereinafter). This was done using a high-energy ball mill to reduce particle size drastically. Cold isostatic pressing was used to compact the milled powder which resulted in a significant increase in the density. X-ray diffraction confirmed single phase with cubic perovskite structure. Particle size was measured from TEM images. Morphological studies were carried out by SEM analyses to observe the grain structure. Of these two syntheses methods, PLZT 12/65/35 ceramics prepared via high energy ball milling exhibited significantly higher dielectric constant, surpassing the previously reported values and also exhibited low remnant polarization value, negligible piezoelectric charge coefficient at room temperature. High temperature dielectric measurements at various frequencies confirm the relaxor behavior of PLZT 12/65/35 ceramics. Ferroelectric cathode configuration based on PLZT 12/65/35 ceramics with high relative permittivity allowed us to achieve exceptionally high current density and power obtained in Radio frequency range.

Possible Extrinsic Ferroelectric-like Signals Originated from the Oxygen Vacancy Drift in HfO2-Based Films

It is generally accepted that oxygen vacancies (VO) play a central role in the emergence of ferroelectricity for HfO2-based materials, but the underlying mechanism still remains elusive. Herein, starting from the basic characterization circuit, we propose a possible extrinsic source of the ferroelectric-like signals. A key finding is that charged VO oscillate within the sample under repeated electric pulses, yielding a nonlinear current which behaves similar to the polarization current for a normal ferroelectric. This unwanted current signal results in a ferroelectric-like hysteresis loop with both remnant polarization and coercive field in good agreement with experimental values, given a charged VO concentration in the vicinity of 1 × 1020 cm–3. Moreover, it is possible to exploit this mechanism to reproduce the scattered remnant polarization values and the effects of wake-up, split-up, and limited endurance that are of crucial relevance for the device applications.