Effect of lanthanum substitution on microstructure and electrical properties of (Bi0.5Na0.5)1−1.5xLaxTi0.41Zr0.59O3 ceramics

Bismuth sodium zirconate (BNZ) based ceramics with a composition of (Bi_0.5Na_0.5)_1?1.5xLa_xTi_0.41Zr_0.59O₃ where x = 0, 0.005, 0.01, 0.02 and 0.03 were prepared by a solid-state mixed oxide method and sintered at the temperature of 900 °C for 2 h. All the samples had relative density between 91 and 97% of their theoretical values. Phase analysis using X-ray diffraction indicated single rhombohedral or pseudo-cubic perovskite structure. SEM showed that addition of La caused the average grain size of the BNTZ ceramics to decrease as well as an improvement of sample density. Dielectric properties at room temperature measured at 10 kHz indicated that addition of La increased the dielectric constant. The results of ferroelectric characterization also revealed that adding La caused a decrease in coercive field without affecting the remanent polarization.     

Excellent Transmittance Induced Phase Transition and Grain Size Modulation in Lead‐Free (1–x)(K0.5Na0.5)NbO3–xLaBiO3 Ceramics

A novel lead‐free excellent transmittance electro‐optic ceramics (1–x)(K_0.5Na_0.5)NbO₃–xLaBiO₃ (KNN‐LB, x = 0.000, 0.005, 0.010, 0.015, 0.020, 0.025, 0.040, 0.060) were fabricated by traditional pressureless ceramics processing procedure. The effects of LaBiO₃ dopant concentration x on the microstructure, phase transition, optical property, and electrical properties were studied systematically. The X‐ray diffraction results indicated that the KNN‐LB ceramics with x ≥ 0.025 have the pseudocubic phase. The morphology, density, and microstructure of the KNN‐LB ceramics were characterized by scanning electronic microscopy and optical microscopy. In particular, the KNN‐LB ceramics (0.05 mm thickness) with x = 0.025 exhibited the highest transmittance of 74.00% in the visible spectrum comparable to the 72.00% transmittance of the lead lanthanum zirconate titanate (PLZT 9/65/35 of 0.127 mm thickness). In addition, the related mechanism of transparency variation induced by phase transition and grain size modulation were discussed thoroughly. Finally, the dielectric and ferroelectric properties of as‐prepared KNN‐LB ceramics were also investigated to further clarify the relationship between transparency and relaxor behavior.     

Structure and ferroelectric behaviour of Na0.5Bi0.5TiO3-KNbO3 ceramics

Lead-free piezoelectric ceramics, (1?x)Na_0.5Bi_0.5TiO₃-xKNbO₃ (NBT-xKN), with x?=?0.02–0.08 were fabricated by solid-state reaction and sintering. The crystal structures and dielectric properties were measured for different KN contents. All compositions in the unpoled, as-sintered state were found to be single-phase pseudo-cubic. However, typical ferroelectric behaviour, with well-saturated polarisation-electric field hysteresis loops, was observed for certain compositions at high electric field levels. It is shown using high-energy synchrotron X-ray diffraction that the application of the electric field induced an irreversible structural transformation from the nano-polar pseudo-cubic phase to a ferroelectric rhombohedral phase. The changes in lattice elastic strain and crystallographic texture of a poled NBT-0.02KN specimen as a function of the grain orientation, ψ, conform well to those expected for a conventional rhombohedrally distorted perovskite ferroelectric ceramic. The dielectric permittivity-temperature relationships for all compositions exhibit two transition temperatures and a frequency-dependent behaviour that is typical of a relaxor ferroelectric. The transition temperatures and grain size decrease with the increasing KN content.     

Structural,magnetic and dielectric properties of Cr substituted yttrium iron garnets

Chromium substituted polycrystalline Yttrium Iron Garnets (Y₃Fe_5–xCr_xO₁₂ with x = 0 to 0.5) were prepared in single‐phase form with lattice constant in the range of 12.3775 Å to 12.3560 Å. All samples exhibit ferrimagnetic transition with transition temperature (T_c) in the range of 547 K for x = 0 to 494 K for x = 0.5. The saturation magnetization value at room temperature is found to increase with Cr concentration that is, from 24.8 to 26.6 emu/g and this is attributed to the preferential occupation of Cr³⁺ ions at octahedral site of Fe³⁺ ions. The frequency dependence of impedance data shows the relaxation and thermal activation of charge carriers across grains and grain boundaries. The complex impedance spectra were modeled by considering equivalent circuits having contributions from the resistance and constant phase element due to grains and grain boundaries and capacitance across grain boundaries. The dielectric constant is found to increase from 20 to 52 as the Cr concentration is increased and it is attributed to hopping of charge carriers across Fe²⁺–Fe³⁺ centers. The Arrhenius plots of relaxation time of charge carriers and conductivity show an anomaly in the vicinity of ferrimagnetic transition temperature and it highlights the presence of magneto‐electric coupling.     

Defect dipoles induced high-energy storage density in Mn-doped BST ceramics prepared by spark plasma sintering

Ba_0.5Sr_0.5TiO₃ ceramics with different Mn-doping amount (Ba_0.5Sr_0.5Ti_1-xMn_xO₃, x = 0, 0.1%, 0.3%, 0.5%) were prepared by spark plasma sintering method. The single phase with cubic structure symmetry was confirmed and a gradual increase in lattice parameter with increasing x was observed. Fine grains with dense microstructure were revealed from the SEM images, while an obvious increase in grain size was detected when x = 0.5%. An optimized doping amount of 0.3% was determined, showing high dielectric constant (ε_r ≈ 2190), low dielectric loss (tanδ ≈ 2.78 × 10⁻³), enhanced breakdown strength (290 kV/cm), and high-energy storage density (1.69 J/cm³) at room temperature. A possible mechanism, namely defect dipoles formation mechanism, was employed to explain the optimization of energy storage performance, and further confirmed from the variation in AC conductivity.     

(BaTiO3)1-x + (Co0.5Ni0.5Nb0.06Fe1.94O4)x nanocomposites: Structure,morphology, magnetic and dielectric properties

Two phase-based nanocomposites consisting of dielectric barium titanate (BaTiO₃ or BTO) and magnetic spinel ferrite Co_0.5Ni_0.5Nb_0.06Fe_1.94O₄ (CNNFO) have been synthesized through solid state route. Series of (BaTiO₃)_1-x + (Co_0.5Ni_0.5Nb_0.06Fe_1.94O₄)_x nanocomposites with x content of 0.00, 0.25, 0.50, 0.75, and 1.00 were considered. The structure has been examined via X-rays diffraction (XRD) and indicated the occurrence of both perovskite BTO and spinel CNNFO phases in various nanocomposites. A phase transition from tetragonal BTO structure to cubic structure occurs with inclusion of CNNFO phase. The average crystallites size of BTO phase decreases, whereas that for the CNNFO phase increases with increasing x in various nanocomposites. The morphological observations revealed that the porosity is highly reduced, and the connectivity between grains is enhanced with increasing x content. The optical properties have been investigated by UV−vis diffuse reflectance spectroscopy. The deduced band gap energy (E_g) value is found to reduce with increasing the content of spinel ferrite phase. The magnetic as well as the dielectric properties were also investigated. The analysis showed that CNNFO ferrite phase greatly affects the magnetic properties and dielectric response of BTO material. The obtained findings can be useful to enhance the performances of magneto-dielectric composite-based systems.     

Ergodicity of fine-grained canonical relaxor ferroelectric (Bi0.5Na0.5)1-xBaxTiO3 films

The drastic reduction in dimensions in thin films, together with the low crystallization temperatures used, normally results in a large reduction in the grain size. It has been reported that relaxor ferroelectric states are stabilized at room temperature for fine-grained ceramics and films that behave as normal ferroelectrics for large grains. In this work, the effects of the grain size reduction on the relaxor characteristics are analyzed for a composition that is already a canonical relaxor with a nonergodic state at room temperature: (Bi_0.5Na_0.5)_1-xBa_xTiO₃ (BNBT). The comparison of the local polar ordering within BNBT grains studied with piezoresponse force microscopy on large-grained ceramics and fine-grained thin films shows that the development of stable long-range ferroelectric order with the application of an electric field is hampered due to the small grain size of the grains. The ergodic character of the high-temperature phase is thus stabilized at room temperature, following a similar mechanism as the one discussed for other noncanonical relaxors.     

Phase structure and electrochemical performance of layered-spinel integrated LiNi0.5Mn0.5O2-LiMn1.9Al0.1O4 composite cathodes for lithium ion batteries

In recent years, multi-component integrated composite cathodes for lithium ion batteries have attracted considerable attention. In this work, novel layered-spinel integrated cathode materials of (1−x)LiNi_0.5Mn_0.5O₂-xLiMn_1.9Al_0.1O₄ were synthesized by a sol-gel method, and their phase structures, morphologies and electrochemical performance were investigated. The crystal structure of the (1−x)LiNi_0.5Mn_0.5O₂-xLiMn_1.9Al_0.1O₄ is changed from layered to spinel structure with increasing x. All the samples exhibit nanoscale grains with the minimum grain size of ~130 nm when x = 0.5. The composite electrode with x = 0.5 exhibits the optimal discharge capacity, presenting a large initial discharge capacity of 236 mAh g⁻¹ at the current density of 20 mA g⁻¹. Good rate capability is also obtained at the composite electrode with x = 0.5 where the electrode displays the relatively high discharge capacity of 64.9 mAh g⁻¹ at the high rate of 5 C. The improved electrochemical performance is related to the introduction of spinel structure into layered structure and small grain size. The spinel structure can stabilize the layered structure, which leads to the improvement in the electrochemical performance of the composites; and the small grain size in the sample with x = 0.5 provides short lithium ion diffusion way and thus enhances the electrochemical performance.     

Lead‐free (K,Na)NbO3‐based ceramics with high optical transparency and large energy storage ability

Highly transparent lead‐free (1‐x)K_0.5Na_0.5NbO₃–xSr(Zn_1/3Nb_2/3)O₃ (KNN–xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically clear, showing high transmittance in the visible and near‐infrared regions (~70% and ~80% at 0.5 mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo‐cubic phase structure as well as the dense and fine‐grained microstructure. In addition, a high energy storage density of 3.0 J/cm³ has been achieved for the 0.94K_0.5Na_0.5NbO₃–0.06Sr(Zn_1/3Nb_2/3)O₃ ceramics with submicron‐sized grains (~136 nm). The main reason is likely to be the typical relaxor‐like behavior characterized by diffuse phase transition, in addition to the dense and fine‐grained microstructure. This study demonstrates that the 0.94K_0.5Na_0.5NbO₃–0.06Sr(Zn_1/3Nb_2/3)O₃ ceramic is a promising candidate of lead‐free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications.     

Physical and electrical properties of Nb doped Bi0.5Na0.5[Zr0.59Ti0.41]O3

This research studied the effect of Nb doping on Bi_0.5Na_0.5[Ti_0.41Zr_0.59]O₃ (when Nb concentration = 0.00, 0.01, 0.03, 0.05, 0.07 and 0.09 mol fraction). Nb doped BNTZ ceramics were fabricated using a conventional mixed-oxide method. All samples were calcined at a temperature of 700 °C for 2 h and sintered at a temperature of 900 °C for 2 h. X-ray diffraction patterns suggested that the compounds possessed rhombohedral perovskite structure. SEM micrographs indicated that average grain size decreased as the amount of Nb additives increased. The electrical resistivity showed a decreasing trend with increasing Nb concentration due to excess charge present in the sample. The dielectric constant and dielectric loss of samples showed no particular trend when Nb was added but the optimum was observed when 0.05–0.07 Nb mol fraction was present in BNTZ ceramics. In this study, both microstructure and donor-type effects played an important role in determining electrical resistivity and dielectric properties of these ceramics.     

Influences of phase transition and microstructure on dielectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Zr<Subscript>1-x</Subscript>Ti<Subscript>x</Subscript>O<Subscript>3</Subscript> ceramics

Bismuth sodium zirconate titanate ceramics with the formula Bi_0.5Na_0.5Zr_1-xTi_xO₃ [BNZT], where x = 0.3, 0.4, 0.5, and 0.6, were prepared by a conventional solid-state sintering method. Phase identification was investigated using an X-ray diffraction technique. All compositions exhibited complete solubility of Ti⁴⁺ at the Zr⁴⁺ site. Both a decrease of unit cell size and phase transition from an orthorhombic Zr-rich composition to a rhombohedral crystal structure in a Ti-rich composition were observed as a result of Ti⁴⁺ substitution. These changes caused dielectric properties of BNZT ceramics to enhance. Microstructural observation carried out employing SEM showed that average grain size decreased when addition of Ti increased. Grain size difference of BNZT above 0.4 mole fraction of Ti⁴⁺ displayed a significant increase of dielectric constant at room temperature.     

Microstructure and electrical conductivity of A-site fully stoichiometric Na0.5+xBi0.5−xTiO3−δ with different Na/Bi ratios

The effect of nominal Na/Bi ratio on the microstructure and electrical conductivity of A-site fully stoichiometric sodium bismuth titanates, Na_0.5+xBi_0.5?xTiO_3?δ, was investigated in this study. Bulk samples with x?=?0, 0.01, 0.03, 0.05, 0.07, and 0.1 were prepared by conventional solid state reaction method. The as-calcined powders primarily exhibited the perovskite structure, which was identified by X-ray diffraction. Electron microscopic investigation of the sintered samples, however, revealed the presence of secondary phases, the amounts of which were found to increase with increasing Na/Bi ratio. Further elemental analysis by energy dispersive spectroscopy indicated that the secondary phases were mainly composed of sodium titanates with different Na/Ti ratios. The grain bulk and grain boundary conductivities of Na_0.5+xBi_0.5?xTiO_3?δ, measured by two-probe AC electrochemical impedance spectroscopy, significantly increased with increasing Na/Bi ratio when x?≤?0.03, but remained almost constant at higher x. The synergetic effect of oxygen vacancy creation, grain size reduction, and secondary phase formation on the variation in the conductivity upon increasing the nominal Na/Bi ratio in Na_0.5+xBi_0.5?xTiO_3?δ was discussed.     

Structure,electrical, and thermal expansion properties of PZnTe–PZT ternary system piezoelectric ceramics

xPb(Zn_0.5Te_0.5)O₃–(1?x)Pb(Zr_0.5Ti_0.5)O₃ (PZnTe–PZT) ceramics were prepared by the solid‐state reaction method. The phase structure, microstructure, ferroelectric and dielectric properties and thermal expansion properties were systematically investigated. X‐ray diffraction analysis showed the morphotropic phase boundary (MPB) existed at the composition of x = 0.08, which was the coexistence of the rhombohedral phase and the tetragonal phase. The grain size of ceramics decreased rapidly from 10‐20 μm to 1‐3 μm when the PZnTe was added in. The PZnTe–PZT ceramics at the MPB composition showed the largest high field effective piezoelectric coefficient and the lowest strain hysteresis H. The dielectric permittivity and phase transition temperature exhibited strongly compositional dependence. A good linear relation was shown in T_m temperature vs x content and a DPT behavior was found in xPZnTe–(1?x)PZT (x = 0.02‐0.08). The thermal expansion properties showed a low thermal expansion coefficient in the low temperature while a high thermal expansion coefficient in the high temperature. Besides, the thermal expansion curve also showed the characteristic of DPT in PZnTe–PZT ceramics.     

The effect of morphotropic phase boundary on dielectric properties of Bi0.5Na0.5Ti1−xZrxO3 solid solutions

Lead-free bismuth sodium titanate zirconate (Bi_0.5Na_0.5Ti_1?xZr_xO₃ or BNTZ) solid solutions with varied composition of x=0.50, 0.55, 0.58, 0.60, 0.63, 0.65, 0.68, 0.70, 0.73, 0.75 and 0.78 mol fraction were obtained using a conventional mixed-oxide method. XRD analysis indicated that the increase in concentration of Zr led to compositions across morphotropic phase boundary region. A quantitative structural investigation was carried out using the X-ray powder diffraction data. The rhombohedral phase was found to dominate for x<0.68 with space group R3c. In the morphotropic phase boundary (MPB) region i.e. 0.68≤x≤0.75, it was demonstrated that coexistence of rhombohedral and orthorhombic phase was observed. For x=0.78, the phase was completely orthorhombic with space group Pmna. Furthermore, the dielectric properties showed some enhanced activity of dipole movement at MPB boundaries which supported the presence of MPB region in this material system.     

Structure,dielectric and ferroelectric properties of 0.92Na0.5Bi0.5TiO3–0.06BaTiO3–0.02K0.5Na0.5NbO3 lead-free ceramics: Effect of Co2O3 additive

0.92Na_0.5Bi_0.5TiO₃–0.06BaTiO₃–0.02K_0.5Na_0.5NbO₃+x wt% Co₂O₃ (NBKT–xCo, x=0, 0.2, 0.4, 0.6, 0.8) lead-free ferroelectric ceramics were prepared via a conventional solid state reaction method. Effects of Co₂O₃ additive on crystallite structure, microstructure, dielectric and ferroelectric properties of the NBKT–xCo ceramics were studied. X-ray diffraction results showed that the rhombohedral–tetragonal morphotropic phase boundary existed in all the ceramics, with relative amount of tetragonal phase varying with the content of Co₂O₃. Average grain size, maximum value of dielectric constant, Curie temperature and ferroelectric properties of the ceramics were close related to the content of Co₂O₃. The dielectric anomaly caused by the phase transition between the ferroelectric phase and the so-called “intermediate phase” was observed in the ceramics with x≤0.2, while it disappeared with further increasing x. All the ceramics showed a diffuse phase transition between the “intermediate phase” and the paraelectric phase. The change in the ferroelectric properties with changing the content of Co₂O₃ was discussed by considering the competitive effects among grain size, relative amount of the tetragonal phase and oxygen vacancies.     

Transparency of K0.5N0.5NbO3–Sr(Mg1/3Nb2/3)O3 lead-free ceramics modulated by relaxor behavior and grain size

High transparency was obtained in (1−x)(K_0.5Na_0.5)NbO₃–xSr(Mg_1/3Nb_2/3)O₃ (x=0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08) lead-free ceramics by pressure-less sintering procedure. The effects of Sr(Mg_1/3Nb_2/3)O₃ content on the microstructure, phase transition, optical properties and electrical properties were studied in detail. The X-ray diffraction results showed that the crystal structure of ceramics gradually transformed from orthorhombic phase into pseudo-cubic phase with doping of Sr(Mg_1/3Nb_2/3)O₃. The fine grain microstructure with clear grain boundary was observed in all compositions, while the grain size exhibited significant composition dependence. It was found that a more uniform distribution with smaller grain size was favorable to high optical transmittance, owing to the decreased scattering by grains and grain boundaries. In addition, a strong diffuse phase transformation in KNN-based ceramics induced by Sr(Mg_1/3Nb_2/3)O₃ doping, causing the ceramics become more relaxor-like and transparent. The transmittance and electric properties results indicated that the 0.95(K_0.5Na_0.5)NbO₃–0.05 Sr(Mg_1/3Nb_2/3)O₃ ceramics exhibited higher transmittance (60% in the near-IR region) accompanied with better electrical properties (ε_m=2104, P_r=5.0 μC/cm², d₃₃=92 pC/N).     

Effects of ZnO nanoparticulate addition on the properties of PMNT ceramics

This research was conducted in order to study the effect of ZnO nanoparticulate addition on the properties of 0.9 Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ [PMNT] ceramics. The PMNT ceramics were prepared by a solid-state reaction. The ZnO nanoparticles were added into PMNT ceramics to form PMNT/xZnO (x = 0, 0.05, 0.1, 0.5, and 1.0 wt.%). The PMNT/xZnO ceramics were investigated in terms of phase, microstructure, and mechanical and electrical properties. It was found that the density and grain size of PMNT ceramics tended to increase with an increasing amount of ZnO content. Moreover, a transgranular fracture was observed for the samples containing ZnO, while pure PMNT ceramics showed only a intergranular fracture. An addition of only 0.05 wt.% of ZnO was also found to enhance the hardness and dielectric and ferroelectric properties of the PMNT ceramics.     

Enhanced pyroelectric properties of lead-free BNT-BA-KNN ceramics for thermal energy harvesting

In this work, (1−x)(0.98Bi_0.5Na_0.5TiO₃-0.02BiAlO₃)-x(Na_0.5K_0.5)NbO₃ (BNT-BA-xKNN) lead-free pyroelectric ceramics were prepared by a solid-state reaction method. The effect of Na_0.5K_0.5NbO₃ (KNN) content on microstructure, phase transition, and electrical properties of the BNT-BA-xKNN ceramics were systematically investigated. The results show that the appropriate content of KNN can induce the formation of the tetragonal structure, which results in the decreased ferroelectric-antiferroelectric phase transition temperature as a result of the break of long-range translational symmetry of BNT lattices. Therefore, the ferroelectric and pyroelectric properties of the BNT-BA-xKNN near room temperature are improved. The room-temperature pyroelectric coefficient significantly increases from 3.66 × 10⁻⁴ C/m²/K at x = 0 to 8.04 × 10⁻⁴ C/m²/K at x = 0.02, making a great contribution to the superior pyroelectric energy harvesting. The output energy density in one cycle of the BNT-BA-0.02KNN is 23.32 μJ/cm³, which is twice as high as that of the pristine samples. The enhancement of material properties suggests that the pyroelectric energy harvesting can be efficiently optimized by the adequate control of the phase structure.     

Physical,structural, morphological,magnetic and electrical properties of Co0.5-xNixZn0.5Fe2O4 nanocrystalline ferrites

A series of Co_0.5-xNi_xZn_0.5Fe₂O₄ (x?=?0–0.25 insteps of 0.05) nano crystalline ferrites were synthesized in combustion method using citric acid as fuel. Densities and porosities were calculated using the lattice constant and Archimedes's principle. A linear increase in experimental density and a decrease in porosity were observed with increase in nickel concentration. Cationic distribution was proposed on the basis of theoretical lattice constant and it was correlated with the variation in magnetic and electrical properties of all samples. TEM image of the sample with nickel concentration x?=?0.15 indicated the existence of nano-metric range particles and the sample was characterized with the help of inter-planar spacing(s) from SAED pattern. Morphological and surface analysis was studies using Scanning Electron Microscopy and well developed nearly spherical grains were observed with increase in nickel concentration. Energy Dispersive Spectroscopic (EDS) analysis was performed for all nickel substituted samples and all displayed stoichiometric proportions of ions in the samples as per the chemical composition. Elemental mapping was done for all samples using EDS data. Curie temperature was dropped nearly 90?°C at the end of the series. Initial permeability showed slight variation with an increase in nickel concentration and it remained nearly constant with frequency up to 3?MHz. Magnetic loss was observed to be constant for all samples after 100?kHz. DC Electrical resistivities of all samples were measured and all samples displayed resistivity in the order of 10⁸ Ω-cm. AC resistivity and dielectric studies were conducted from 100?Hz to 5?MHz for all samples. Dielectric constant and losses of all samples exhibited very low values compared to that of conventional ferrites. The electrical properties of all samples were discussed with the help of temperature variation of resistivity, activation energy, grain size, density and porosity.     

Effect of the Amount of H2O on the Crystallization of TiO2 Films Prepared from Alkoxide Solutions Containing Acetylacetone

Sol–gel‐derived TiO₂ films were prepared by dip‐coating from Ti(OC₃H₇ⁱ)₄–CH₃COCH₂COCH₃–HNO₃–H₂O–C₂H₅OH solutions, and the effect of the H₂O content in solutions on the crystallization of TiO₂ films during the heat treatment at 800°C was discussed. The crystalline phase, crystallite size, grain size, and refractive index of the TiO₂ films depended on the H₂O/Ti(OC₃H₇ⁱ)₄ mole ratios (x) in the coating solutions. Highly dense and crystalline rutile films were obtained at x = 0.5–10, where the crystallites and grains became larger with increasing x. The further increase in x from 10 to 50 reduced the crystallite size and refractive index of the films, where anatase phase appeared at x = 30–50.