Increase In Remnant Polarization Research Articles

Co-doping Ce3+ and Mn4+ to induce pseudo tetragonal distortion in CaBi2Nb2O9 for improved piezoresponse

Calcium bismuth niobate (CBN), known for its high Curie temperature (TC), has been investigated as a potential material for vibration sensor due to its ability to operate at elevated temperatures. However, the inherent weakness in piezoresponse of CBN has limited its sensing performance. In this study, a pseudo-tetragonal distortion in CBN was successfully induced by incorporating Ce3+ ions into the (Bi2O2)2+ layers of CBN. This modification led to a change in the interaction between the perovskite and bismuth layers, resulting in enhanced piezoelectric and ferroelectric properties. Further enhancement was achieved by introducing Mn4+ ions into the Ce3+-doped CBN. The co-doped CaBi1.96Ce0.04Nb1.985Mn0.015O9 demonstrated a significantly improved piezoelectric coefficient (d33) of 15.9 pC/N, compared to 6.8 pC/N for pure CBN ceramics, and an increased remnant polarization (Pr) of 20.78 μC/cm2, compared to the 3.83 μC/cm2 of the pure material. This work not only deepens the understanding of bismuth-layer-structured ferroelectrics (BLSFs) but also presents a viable co-doping strategy to enhance the piezoresponse in CBN ceramics. This strategy could pave the way for the development of high-performance, high-temperature vibration sensors and potentially lead to the discovery of more novel BLSFs with superior performance.

Piezoelectric response and figure of merit assessment in lead-free (Ba1-xSrx)(Zr0·025Ti0.975)O3 ceramics with low-level Sr2+ substitutions

This study investigates the effects of low-level Sr2+ substitutions on the microstructures and electrical properties of BSZT ceramics with formula (Ba1-xSrx)(Zr0·025Ti0.975)O3. The ability of BSZT ceramics to convert energy is assessed based on the piezoelectric coefficient, d33 associated with the figure of merit (FOM). BSZT ceramics with 0.00 ≤ x ≤ 0.10 were sintered at 1350 °C for 2 h. The XRD measurement confirmed the formation of a single-crystalline phase in all ceramics. All ceramics stabilized in tetragonal crystal structures with progressive decline in tetragonality. It was found that the ceramic with low-level Sr2+ substitutions demonstrated excellent dielectric, piezoelectric and ferroelectric behaviours before gradually deteriorated at higher contents. Systematic deviation of Sr2+ atomic percentage signified broad dielectric curves compared to pristine Ba(Zr0·025Ti0.975)O3. A significant increase of remnant polarization, Pr value (11.21 ± 0.12 μC/cm2) was recorded when x = 0.02, in line with its highest as-sintered density and tetragonality. High d33 and low ε33 values contributed to an optimum value of piezoelectric voltage, g33 coefficient. Consequently, a high FOM comparable to PZT was obtained. The current work successfully demonstrated the preparation of lead-free ceramics based on BaTiO3 with great potential for energy conversion applications.

Phase structure and electrical properties of BiFeO3–BaTiO3 ceramics near the morphotropic phase boundary

As a promising lead-free high-temperature piezoelectric material, BiFeO3–BaTiO3 (BF-BT) is still under debate on its crystal structure, especially for the compositions in the morphotropic phase boundary (MPB). Herein, the crystal structure of (1-x)BF-xBT ceramics near the MPB with x = 0.20–0.33 was analyzed by X-ray diffraction and Raman spectroscopy. With the addition of BT, the phase transition from distorted rhombohedral to pseudo-cubic structure was determined by Rietveld refinement. Raman analysis showed the weakening interactions between the A-site cations and BO6 octahedron, as well as the degenerated distortions of BO6 octahedron. Intriguingly, the results of X-ray photoelectron spectroscopy suggested the inhibition of Fe3+ reduction and decrease in oxygen vacancy concentration by the incorporation of BT. In terms of the electrical properties, the significant decline in Curie temperature, improvement in permittivity, and reduction in high-temperature dielectric loss can be observed with the increase of BT content. The increased remnant polarization, enhanced dielectric response and decreased coercive field were helpful for the piezoelectric performance. The maximum room-temperature piezoelectric coefficient of ∼160 pC/N and high-temperature piezoelectric coefficient of ∼324 pC/N were acquired in the x = 0.30 ceramics. This work provides a clear scope for further research on the structural transformation and high-temperature piezoelectric applications of BF-BT system.

Multifunctional properties of transition metal based double perovskite ceramics

In this manuscript, iron based double perovskite oxides Ca2Fe1-xNixNbO6(x=0, 0.1) were successfully synthesized adopting the physical mixed oxide route and high temperature annealing. The influence of Ni substitution on the structure, band gap tuning, leakage current, dielectric, energy storage and magnetic properties of the parent ceramic is also discussed. A relatively high remnant polarization of 11.8 µC/cm2 with a reduced band gap of 1.9 eV is noticed in the Ni modified ceramic. It is found that the saturation magnetization increases from 0.359 emug−1 to 0. 892 emug−1 whereas the leakage current density decreases from 6.869E−6 to 5.52E-6 A/mm2 upon Ni substitution. The enhanced saturation magnetization and ferroelectric properties of the modified ceramic with lesser leakage current increases their energy storage capacity. The energy storage efficiency of the Ni substituted material increases from 15.52% to 71% with a reduction of hysteresis loss. Hence the increase in remnant polarization and decrease in band gap of the Ni modified ceramic aligns it toward ferroelectric photovoltaic application.

Systematic investigation of the effect of SnS2 nanofiller content on the piezoelectric performance of the PVDF-TrFE-based nanogenerator

In this work, SnS2 is used as a nanofiller material to improve the response of the polymer-based piezoelectric nanogenerator because of its better inherent piezoelectric properties in comparison to other 2D materials. For this, first, nanoflakes of tin sulfide (SnS2) were synthesized via the hydrothermal method, where the high purity of SnS2 powder is confirmed by Raman spectroscopy and X-ray diffraction studies. The obtained powder of SnS2 was then mixed with PVDF-TrFE in different weight percentages (0%, 1%, 3%, 5%, and 7%) of SnS2 to synthesize polymer composite films via drop-casting method. These films are then characterized with XRD and FTIR spectrometers which show enhancement in the electroactive beta phase of the nanocomposite films after doping of SnS2 powder, from 58.30% to 93.07%, which is in agreement with the polarization versus electric field (P-E) measurements that show increased remnant polarization after doping. These films are then used to fabricate a piezoelectric nanogenerator by adhering aluminum tape on both sides of the films. The piezoelectric nanogenerator's (PENG) output performance is analyzed by measuring the open-circuit voltage (Voc) and short-circuit (Isc) by tapping the nanogenerator with the help of a dynamic shaker, which shows that the output performance of PVDF-TrFE based PENGs gets enhanced after the introduction of SnS2 powder. The maximum output voltage of 14.4 V is obtained corresponding to the PENG with 5 wt% SnS2, which was almost 1.5 times that of the PENG made with bare PVDF-TrFE. The output piezoelectric current follows the similar trend, with the 5 wt% SnS2 PENG producing3.9μA of current, which was roughly 1.62 times more than the output of the bare PVDF-TrFE thin film. As a result, the present study demonstrates that adding SnS2 to the PVDF matrix can significantly improve energy harvesting technologies based on PVDF's piezoelectric properties.

Lead free high Tc piezoelectric Sr2Nb2O7-La2Ti2O7 solid solution: A structural, dielectric ferroelectric and piezoelectric studies

The ferroelectric and piezoelectric properties of Sr2Nb2O7–La2Ti2O7 (SNB-LT) solid solution ceramics have been studied. The La and Ti ions were substituted into the Sr2Nb2O7 (SNB) lattice and their resultant phase of SNB-LT has lattice distortion. The Rietveld refinement parameters from the XRD patterns corroborate a solid solution of Sr2Nb2O7–La2Ti2O7. The addition of La3+ and Ti4+ dampens the SNB intra-structural phase. Raman spectroscopy confirmed the internal lattice relaxation due to the Ti(Nb)O6 octahedron in the lattice. At 2×106 Hz, the dielectric permittivity of SNB-LT-1, SNB-LT-2, and SNB-LT-3 is 17.2, 17.5, and 21.3, respectively, with σac conductivity in the order of 10−5 S/m. With an increase in Ti(Nb)O6 distortion, the piezoelectric coefficient of SNB-LT-1, SNB-LT-2, and SNB-LT-3 increases linearly as 6.3, 8.1, and 9.3 pC/N. The temperature-dependent ferroelectric polarization of SNB-LT-1, SNB-LT-2, and SNB-LT-3 has been tested, and a substantial rise in polarization has been demonstrated up to 120 °C. At 120 °C, the SNBLT solid solution showed a two-fold increase in remnant polarization.

Remote Oxygen Scavenging of the Interfacial Oxide Layer in Ferroelectric Hafnium-Zirconium Oxide-Based Metal-Oxide-Semiconductor Structures.

Discovery of ferroelectricity in HfO2 has sparked a lot of interest in its use in memory and logic due to its CMOS compatibility and scalability. Devices that use ferroelectric HfO2 are being investigated; for example, the ferroelectric field-effect transistor (FEFET) is one of the leading candidates for next generation memory technology, due to its area, energy efficiency and fast operation. In an FEFET, a ferroelectric layer is deposited on Si, with an SiO2 layer of ∼1 nm thickness inevitably forming at the interface. This interfacial layer (IL) increases the gate voltage required to switch the polarization and write into the memory device, thereby increasing the energy required to operate FEFETs, and makes the technology incompatible with logic circuits. In this work, it is shown that a Pt/Ti/thin TiN gate electrode in a ferroelectric Hf0.5Zr0.5O2 based metal-oxide-semiconductor (MOS) structure can remotely scavenge oxygen from the IL, thinning it down to ∼0.5 nm. This IL reduction significantly reduces the ferroelectric polarization switching voltage with a ∼2× concomitant increase in the remnant polarization and a ∼3× increase in the abruptness of polarization switching consistent with density functional theory (DFT) calculations modeling the role of the IL layer in the gate stack electrostatics. The large increase in remnant polarization and abruptness of polarization switching are consistent with the oxygen diffusion in the scavenging process reducing oxygen vacancies in the HZO layer, thereby depinning the polarization of some of the HZO grains.

Switchable ferroelectric photovoltaic in the low bandgap cobalt-substituted BiFeO3 epitaxial thin films

The proposal of the ferroelectric photovoltaic effect provides a spick-and-span concept for breaking through the bottleneck of traditional heterojunction energy conversion and the photoelectric memory device. However, the wide bandgap, low carrier transport capacity, and small photocurrent of ferroelectric materials limit its ferroelectric photovoltaic applications. Here, chemical regulation of cobalt substitution has been used to effectively reduce bandgap and improve ferroelectric photovoltaic properties. High-quality Co-substituted BiFeO3 epitaxial films were fabricated by magnetron sputtering. The enhanced tetragonality can be obtained by introducing the chemical strain of cobalt. The ferroelectric properties of present films have been significantly improved with a fivefold increase in remnant polarization, resulting from the enhanced lattice distortion of the oxygen octahedron. The enhanced hybridization of electron orbitals and the atomic structure has been revealed by synchrotron radiation and the high-resolution HAADF-STEM. Intriguingly, the optical bandgap has been reduced from 1.97 eV to1.47 eV, which is close to the ideal bandgap. The switchable ferroelectric photovoltaic can be realized by changing the direction of polarization, and the open-circuit voltage and short-circuit current have increased to 1.7 and 1.8 times, respectively. This work further reveals the application potential of chemical-strain-modulated epitaxial films in the field of optoelectronics and information storage.

Ferroelectric ZrO2 ultrathin films on silicon for metal-ferroelectric-semiconductor capacitors and transistors

Enhanced ferroelectric properties of nanoscale ZrO2 thin films by an HfO2 seed layer are demonstrated in metal-ferroelectric-semiconductor (Si) capacitors and transistors prepared with a low thermal budget of 400 °C. The seeding effect of the HfO2 layer leads to the enhancement of crystallization into the orthorhombic phase and the increase of remnant polarization of the sub-10 nm ZrO2/HfO2 bilayer structure. The ferroelectric field-effect transistor with the ZrO2/HfO2 bilayer gate stack reveals a large memory window of ~1.2 V and a steep subthreshold swing below 60 mV/decade. As compared with the Hf0.5Zr0.5O2 thin film, superior ferroelectric properties of the ZrO2/HfO2 bilayer structure show great potential for ferroelectric memory devices fabricated on Si substrates.

Effects of post cooling on the remnant polarization and coercive field characteristics of atomic layer deposited Al-doped HfO2 thin films

A study was conducted on how the cooling rate after the phase change heat treatment required to secure the ferroelectric (FE) properties affects the ferroelectricity of Al-doped HfO2 (Al:HfO2) thin films. When cooling the thin film to room temperature after heat treatment, the cooling rate was controlled through slow chamber cooling, which maintains and cools the sample inside the heat treatment equipment, slightly faster air cooling, and rapid cooling using deionized water. We achieved the dramatic increase of remnant polarization (Pr) and coercive electric field (Ec) using rapid quenching after phase change heat treatment. The 2Pr and 2Ec values of rapid quenched FE Al:HfO2 thin film are approximately ∼100 μC/cm2 and ∼9.5 MV/cm, respectively, which are the highest records among HfO2-based FE thin films reported so far. These significant improvements are attributed to inducing homogeneously distributed defects complexes and higher stress/confinement strain within Al:HfO2 thin film, leading to preventing pinched hysteresis loop and stabilize orthorhombic crystal structure. Furthermore, endurance up to 2 × 106 cycles and reasonable projected 10 years retention properties were achieved, stably without wake-up and fatigue in quenched FE Al:HfO2 capacitor. These results propose a beneficial method to improve the ferroelectricity of HfO2-based thin films.

Dielectric and energy storage characteristics of 0.2, 0.4, 0.6, 0.8 wt% Cr2O3 doped PbZr0.52Ti0.48O3 ceramics synthesized by spark plasma sintering

The microstructure, phase analysis, impedance and modulus spectroscopies, dielectric and energy storage characteristics have been carried out on Cr2O3 doped PbZr0.52Ti0.48O3 (PZT) ceramics. The PbZr0.52Ti0.48O3 + x Cr2O3 (x = 0.2, 0.4, 0.6 and 0.8 wt%) ceramics were synthesized by solid state reaction method following spark plasma sintering technique. The particle size of calcined powders lies between 200 nm and 500 nm, and the particles have largely faceted morphology. The analysis of X-rays diffraction patterns of the ceramics reveals perovskite structure with tetragonal lattice having P4mm space group. No additional peak related to Cr- based compound has been detected, which indicates Cr solubility in the PZT solid solution. The Cr2O3 doped PZT samples exhibit ≥ 99.3 % relative density with average grain size lower than that of undoped PZT samples reported. The peak value of dielectric permittivity (εm) was found to decrease when the Cr2O3 content is above 0.2 wt%; however, it increases for 0.8 wt% Cr2O3 doped sample. Such behavior is explained based on the multivalent nature of chromium ions. The impedance and modulus spectroscopic analyses reveal the contributions of grain relaxation and confirm the non-debye type of relaxation. The modulus studies reveal the presence of hopping mechanism in the material. The DC conductivity curves show a typical Arrhenius type behavior of electrical conductivity. The energy storage studies reveal an increase in remnant polarization and coercive field for samples containing up to 0.6 wt% Cr2O3 and the results are in agreement with the XPS observations. The highest energy storage density (∼0.1 J/cm3) and efficiency (∼64%) under an electric field of 25 kV/cm were observed for 0.2 wt% and 0.8 wt% Cr2O3 doped PZT samples, which are attributed to the dominant presence of donor Cr5+ ion.

Thickness Dependence of Ferroelectric and Optical Properties in Pb(Zr0.53Ti0.47)O3 Thin Films.

As a promising functional material, ferroelectric Pb(ZrxTi1−x)O3 (PZT) are widely used in many optical and electronic devices. Remarkably, as the film thickness decreases, the materials’ properties deviate gradually from those of solid materials. In this work, multilayered PZT thin films with different thicknesses are fabricated by Sol-Gel technique. The thickness effect on its microstructure, ferroelectric, and optical properties has been studied. It is found that the surface quality and the crystalline structure vary with the film thickness. Moreover, the increasing film thickness results in a significant increase in remnant polarization, due to the interfacial layer effect. Meanwhile, the dielectric loss and tunability are strongly dependent on thickness. In terms of optical properties, the refractive index of PZT films increase with the increasing thickness, and the photorefractive effect are also influenced by the thickness, which could all be related to the film density and photovoltaic effect. Besides, the band gap decreases as the film thickness increases. This work is significant for the application of PZT thin film in optical and optoelectronic devices.

Effects of glass additives on microstructure, dielectric and ferroelectric properties of BaTiO3–BiYbO3 based ceramics

(100–x) wt% (0.95BT–0.05BY)–x wt% (0.5MgO–0.5SiO2) (x = 0, 1, 2, 4, 8) ceramics were fabricated by using a solid-state synthesis method. The effects of the MgO–SiO2 doping on the microstructure, the ferroelectric, and the dielectric properties of BT–BY ceramics were investigated in detail. The results show that the relative permittivity initially decreases and then increases again upon the increase in the MgO–SiO2 content. The addition of the MgO–SiO2 glass oxide dopant enhances the frequency and the temperature stability of the relative permittivity of BT–BY ceramics. Moreover, the coercive field and the remnant polarization increase and then decrease with increasing MgO–SiO2 dopant content, while the slim P–E loops are observed when x ≥ 2. The largest values for the remanent polarization (1.2 μC cm−2) and the coercive field (9.18 kV cm−1) are obtained at x = 1. The addition of MgO–SiO2 can induce a small leakage current in the BT–BY ceramic when x ≥ 2. The breakdown strength increases with decreasing grain size when MgO–SiO2 is added moderately. Its value increases from 80 kV cm−1 up to 100 kV cm−1 when x changes from 0 to 8. The energy storage density and efficiency of the (100–x) wt% (0.95BT–0.05BY)–x wt% (0.5MgO–0.5SiO2) ceramics decrease and then increase with increasing x. The maximum values of the electrical energy storage density (0.24 J cm−3) and energy efficiency (85.77%) are obtained when x = 8.

Microstructure, Enhanced Relaxor-Like Behavior and Electric Properties of (Ba0.85Ca0.15)(Zr0.1−xHfxTi0.9)O3 Ceramics

(Ba0.85Ca0.15)(Zr0.1−xHfxTi0.9)O3 (BCZHT) ceramics were fabricated by a conventional solid-state reaction method. The effects of Hf4+ on microstructure and electric properties of BCZHT ceramics have been systematically investigated. The x-ray diffraction (XRD) results indicate that the introduction of Hf4+ in BCZHT ceramics induces phase transition from an orthorhombic phase to the coexistence of tetragonal and orthorhombic phases, and the lattice constant decreases with the increasing of Hf4+ content caused by substitution of Hf4+ for Zr4+ at B sites. As Hf4+ content increases, the densification of BCZHT ceramics is enhanced and the grain size increases. The introduction of Hf4+ at B sites results in the fall of the Curie temperature and the increase of dielectric constant in BCZHT ceramics. The temperature dependences of dielectric properties of BCZHT (x = 0, 0.05 and 0.1) ceramics show obvious diffuse phase transition characteristics, and the diffuseness of phase transition is enhanced with increasing of Hf4+ content. But there is no frequency dispersion phenomenon in BCZHT (x = 0, 0.05 and 0.1) ceramics. The substitution of Hf4+ for Zr4+ at B sites of BCZHT ceramics makes its remnant polarization increase, which results from the interaction of increased grain size and tolerance factor. When temperature is above its Curie temperature, the polarization–electric field curves of BCZHT (x = 0, 0.05 and 0.1) ceramics still show nonlinear characteristics, which further proves that there is diffuse phase transition and relaxor-like behavior. Moreover, the piezoelectric coefficient of BCZHT ceramics increases as Hf4+ content increases.

BST-P(VDF-CTFE) nanocomposite films with high dielectric constant, low dielectric loss, and high energy-storage density

Free-standing, flexible, and transparent ceramic-polymer nanocomposite films with a uniform thickness of about 5 μm were fabricated using a simple spin-coating process, in which the polymer solution with a high concentration was used. Ba0.5Sr0.5TiO3 (BST) nanoparticles and P(VDF-CTFE) 91/9 mol.% (VC91) copolymer were used as ceramic filler and polymer matrix, respectively. Microstructures, dielectric properties, and energy-storage performances of the BST-VC91 nanocomposite films have been investigated. With increasing volume fraction of BST, the dielectric constant increases, while the dielectric loss decreases. A dielectric constant of about 38.4 at 100 Hz associated with a dielectric loss of only about 0.02 was obtained in the nanocomposite film with 40 vol% of BST. It is experimentally found that the temperature dependences and the frequency dispersions of dielectric properties were strongly influenced by the volume fraction of BST, especially at high temperatures. Good temperature stability and small frequency dispersion of dielectric constant can be obtained in the BST-VC91 nanocomposite films with 40 vol% and 50 vol% of BST, which are also associated with a low dielectric loss. It is concluded that the motion of the polymer chains is the micro-origin of the relaxation process observed at high temperatures. With increasing volume fraction of BST, the dielectric breakdown strength decreases, while the maximal polarization and remnant polarization increase. The maximal charge-energy density and discharge-energy density of about 21.7 J/cm3 and 7.5 J/cm3 are obtained in the BST-VC91 nanocomposite film with 30 vol% BST under 2500 kV/cm, which are more than 2 times larger than those observed in pure VC91 film under the same electric field.

Enhanced ferroelectric relaxor behavior of Ho2O3-modified barium zirconate titanate ceramics

Ho2O3 doped Ba(Zr0.1Ti0.9)O3 ceramics were prepared by conventional solid state reaction route and their microstructure, dielectric properties and ferroelectric properties were investigated with the variation of Ho2O3 content using X-ray diffraction, scanning electron microscope, LCR measuring system and ferroelectric tester. It is found that the Ho3+ ions initially substitute the B-site host ions maintaining the perovskite structure in Ba(Zr0.1Ti0.9)O3 ceramics and then contribute to the formation of secondary phase with the continuous increase of Ho2O3 content. The average grain size decreases significantly as the Ho2O3 concentration increases. The ferroelectric-paraelectric phase transition temperature Tm of Ba(Zr0.1Ti0.9)O3 ceramics decreases with increasing Ho2O3 content. Based on the increase of critical exponent γ from the modified Curie–Weiss equation as well as the increase of deviation from Curie–Weiss law, the diffuse phase transition behavior is enhanced with increasing Ho2O3 content, indicating a composition-induced diffuse transition. A normal ferroelectric behavior with diffuse phase transition is obtained for the undoped Ba(Zr0.1Ti0.9)O3 ceramics. However, the relaxor-like ferroelectric behavior with a strong frequency dispersion of relative permittivity maximum ermax at T < Tm and a strong diffuse phase transition is found for Ba(Zr0.1Ti0.9)O3 ceramics with high Ho2O3 content. The high Ho2O3 content ceramics obey the empirical Vogel–Fulcher relation, which confirms the relaxor behavior of Ba(Zr0.1Ti0.9)O3 ceramics with high Ho2O3 content. The remnant polarization increases and then decreases with the increasing Ho2O3 content while the coercive field decreases with the increase of Ho2O3 content in Ba(Zr0.1Ti0.9)O3 ceramics.

Origin of enhanced piezoelectric properties and room temperature multiferroism in MnO2 added 0.90(Li0.12Na0.88NbO3)-0.10BaTiO3 ceramic

Room temperature multiferroism with enhanced ferro and piezoelectric properties of a new lead-free MnO2 added 0.90(Li0.12Na0.88NbO3)-0.10BaTiO3 ceramic is reported. The addition of MnO2 as an additive resulted in a two fold increase in remnant polarization (Pr) (from ~7.30 to 17.20μC/cm2), ~50% increase in large-signal piezoelectric coefficient (d33∗) (from ~117 to176pm/V) and symmetric butterfly loop are observed. Phase analysis revealed that MnO2 entered the host lattice as Mn2+ and Mn4+-ions and induced room temperature ferromagnetic-like character. Interestingly, an intrinsic coupling between the two ferroic orders is evidenced by the observation of a magneto-electric voltage coefficient (αE) of ~0.94mV/cm.Oe.

Structure, piezoelectric performance and liquid phase aid sintering of SiO2 doped (K0.5Na0.5) NbO3 lead-free ceramics

The structure, piezoelectric and sintering proprieties of Lead-free piezoelectric (K0.5Na0.5) NbO3 (abbreviated as KNN) ceramic with additive SiO2 (KNN–xSiO2, x = 0, 0.25, 0.50, 0. 75, 1.00, 1.50, 2.00 and 3.00 mol%) were investigated. Though it has a high melting point, the SiO2 was found to be effective on the sintering and piezoelectric performance of KNN lead-free ceramics. The structure characterization indicating that low concentration doping (<2.00 mol%) may not change KNN perovskite structure and liquid phase have appeared between crystalline grains. Furthermore, the sizes of crystalline grains gradually increased and reached to maximum when x = 0.75 mol% with indistinct grain boundaries on account of liquid phase. And the density properties of KNN ceramic were dramatically enhanced because of occurrence of liquid phase. The dielectric properties have achieved improvement obviously due to large resistivity and decreased structure loss results from the appearance of liquid phase as well. And ferroelectric properties have still achieved to enhancement including increased remnant polarization P r and decreased coercive field E c when appropriate SiO2 was added into KNLTN ceramic. We obtained the maximum value of piezoelectric coefficient d 33 (115 pC/N) and converse piezoelectric coefficient d * 33 when doping concentration approached to 0.75 mol%.

Enhanced electrical properties in Rb-substituted sodium bismuth titanate ceramics

Influence of large ionic radius cation rubidium (Rb) substitution in the A-site of sodium bismuth titanate (NBT) on remnant polarization and dielectric constant is investigated. Substitution of 0.01 mole fraction of Rb in NBT ceramics escalates remnant polarization and dielectric constant coupled with reduction in coercive field and enhanced piezoelectric constant. Spontaneous and remnant polarization of Rb-substituted NBT ceramics is 66.3 and 59.9 µC/cm2 respectively, which is greater than other isovalent substitution cations in NBT that have been reported in the literature. Room-temperature dielectric constant and piezoelectric constant are 704.68 and 88 pC/N successively. Increase in remnant polarization, dielectric constant and piezoelectric constant along with decreased coercive field is attributed to improved mobility of domain reorientation and domain wall motion due to low homogeneous strain and minimum rhombohedral lattice distortion in Rb-substituted NBT ceramics. The present work provides a reproducible preparation of Rb-substituted ceramics to enhance ferroelectric and dielectric properties for use in functional devices which require high reliability.

Polarization Controlled Electrocatalytic and Photoelectrocatalytic Activity of Ferroelectric Catalyst

The coupling effect between ferroelectric polarization and electrochemical processes makes possible the engineering of charge-carrier conduction characteristics at the heterojunction between a polarized ferroelectric catalyst and a chemical solution. It is well known that ferroelectricity can affect a material's surface physics which result into enhance catalytic properties. Ferroelectric materials have spontaneous polarization, which can be reoriented between equivalent domain states by an applied electric field. Therefore, ferroelectrics are potential material to achieve switchable surface chemistry for electrochemical applications. In this work we are going to present polarization controlled electrocatalytic and photoelectrocatalytic activity of ferroelectric catalyst. The increase in remnant polarization shows appreciable enhancement in the electrochemical and photoelectrochemical activity towards OER in alkaline medium and waste water treatment. The photoelectrocatalytic acitivity was investigated for hazardous pharmaceutical pollutants.