Structure–property relationships of perovskite-structured Ca0.61Nd0.26Ti1-x(Cr0.5Nb0.5)xO3 ceramics

A series of Ca_0.61Nd_0.26Ti_1-x(Cr_0.5Nb_0.5)_xO₃ (CNTCNx) (0 ≤ x ≤ 0.1) ceramics were prepared via a solid state reaction method. All CNTCNx samples were crystallized into the orthorhombic perovskite structure. The SEM micrographs indicated that the average grain sizes of samples depended on (Cr_0.5Nb_0.5)⁴⁺ concentration. And as (Cr_0.5Nb_0.5)⁴⁺ concentration increased, the average grain size of samples decreased significantly. The short range order (SRO) structure and structural distortion of oxygen octahedra proved to exist in CNTCNx crystals from Raman spectra analysis results. The microwave dielectric properties highly depended on the B-site bond strength, oxygen octahedra distortion, reduction of Ti⁴⁺ to Ti³⁺ and internal strain η. At last, the CNTCN0.06 ceramic sintered at 1400 °C for 4 h exhibited good and stable comprehensive microwave dielectric properties of ε_r = 92.3, Q × f = 13,889 GHz, τ_f = + 152.8 ppm/°C.     

Enhanced dielectric and energy-storage properties in ZnO-doped 0.9(0.94Na0.5Bi0.5TiO3−0.06BaTiO3)−0.1NaNbO3 ceramics

[0.9(0.94Na_0.5Bi_0.5TiO₃?0.06BaTiO₃)?0.1NaNbO₃]-xZnO (NBT-BT-NN-xZnO, x=0, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%) ferroelectric ceramics were fabricated using a conventional solid-state reaction method. The effects of ZnO content on dielectric, energy-storage and discharge properties were systematically investigated. Dielectric constant and difference between maximum and remanent polarization were significantly improved by ZnO doping. Dielectric constant of NBT-BT-NN-1.0-wt% ZnO was 3218 at 1 kHz and room temperature, i.e. one time bigger than that of pure NBT-BT-NN ceramic. As a consequence, a maximum energy-storage density of 1.27 J/cm³ with a corresponding efficiency of 67% was obtained in NBT-BT-NN-1.0-wt% ZnO ceramic. Moreover, its pulsed discharge energy density was 1.17 J/cm³, and 90% of which could be released in less than 300 ns. Therefore, ZnO doped NBT-BT-NN ceramic with a large energy-storage density and short release time could be a potential candidate for applications in high energy-storage capacitors.     

Low-temperature-sintered Bi0.5Na0.5TiO3-based lead-free ferroelectric ceramics with good piezoelectric properties

Li₂CO₃ has been used as a sintering aid for fabricating lead-free ferroelectric ceramic 0.93(Bi_0.5Na_0.5TiO₃)-0.07BaTiO₃. A small amount (0.5 wt%) of it can effectively lower the sintering temperature of the ceramic from 1200 °C to 980 °C. Unlike other low temperature-sintered ferroelectric ceramics, the ceramic retains its good dielectric and piezoelectric properties, giving a high dielectric constant (1570), low dielectric loss (4.8%) and large piezoelectric coefficient (180 pC/N). The “depolarization” temperature is also increased to 100 °C and the thermal stability of piezoelectricity is improved. Our results reveal that oxygen vacancies generated from the diffusion of the sintering aid into the lattices are crucial for realizing the low temperature sintering. Owing to the low sintering temperature and good dielectric and piezoelectric properties, the ceramics, especially of multilayered structure, should have great potential for practical applications.     

Resistive,capacitive and conducting properties of Bi0.5Na0.5TiO3-BaTiO3 solid solution

In the present paper, the effect of addition of a small amount (8 wt%) of barium titanate (BT) on electrical properties of bismuth sodium titanate (BNT) forming a solid solution of a composition (0.92)(Bi_0.5Na_0.5TiO₃)+(0.08)(BaTiO₃) (BNT-BT-8) has mainly been reported. The solid solution of BNT-BT-8 was prepared by a cost effective and standard mixed-oxide method. Preliminary structural analysis using X-rays diffraction pattern and data showed the existence of two phases; orthorhombic (major) and tetragonal (minor impurity/secondary) phase. Analysis of scanning electron micrograph and energy dispersive spectrum of the pellet sample reveals the formation of high density with homogeneously distributed grains of varying dimension. The locations, phonon modes statistics, width and intensity of peaks of Raman spectra of BNT-BT-8 was analyzed by Raman spectroscopy and provided some data on molecular structure of the material. The effect of temperature and frequency on some ferroelectric characteristics of the material were studied. The frequency-temperature dependence of electrical characteristical such as impedance of the material was studied by impedance spectroscopy. The electric conductivity follows the Arrhenius equation and provided activation energy at different frequency. The dielectric and impedance spectroscopy suggest the existence of a non-Debye relaxation mechanism in the material.     

High tunability in (1 1 0)-oriented BaZr0.2Ti0.8O3 (BTZ) lead-free thin films fabricated by pulsed laser deposition

Using a pulsed laser deposition method the BaZr_0.2Ti_0.8 O₃ (BTZ) lead–free thin films with a thickness of ~250 nm were grown on FTO, ITO and Pt–Si substrates, respectively. The analysis results of microstructural, dielectric properties and leakage current reveal that the thin films deposited on Pt–Si substrates are oriented growth along the (1 1 0) direction and exhibit the optimal performance characteristics. Calculations of figure of merit (FoM) and dielectric tunability display a maximum value of ~42.8 and ~68.5% at E = 400 kV/cm at room temperature, respectively. The excellent tunable properties, high dielectric constant (~635@ 100 kHz) and low leakage current density of (9.3 × 10^–8 A/cm² at 400 kV/cm) make the (1 1 0)–oriented BaZr_0.2Ti_0.8 O₃ thin film to be an attractive material for applications of tunable devices.     

Electrical and photoluminescence properties of Sm3+ doped Na0.5La0.5Bi8-xSmxTi7O27 ceramics

In this study, Sm³⁺ doped Na_0.5La_0.5Bi_8-xSm_xTi₇O₂₇ (NBT-BITL-xSm, x = 0, 0.01, 0.015, 0.02, and 0.03) ceramics were synthesized via a conventional solid-state reaction process. The structural, electrical, and photoluminescence properties of NBT-BITL-xSm ceramics were systematically investigated. The crystal structure of NBT-BITL-xSm was refined using XRD Rietveld refinement and found to possess a single orthorhombic structure at room temperature. Raman spectroscopy revealed that Sm³⁺ ions preferred to substitute for Bi³⁺ located in the A-sites of pseudo-perovskite layers, inducing a slight decrease in orthorhombic distortion. Strong characteristic emission peaks of Sm³⁺ ions were observed in orange-red regions under a 407 nm laser source, and the sample with x = 0.015 achieved the optimal photoluminescent property. Dielectric measurements showed double anomaly permittivity peaks at the temperature of 589 and 600^°C (T_m and T_c, respectively). The complex impedance spectrum indicated that the electrical conductivities mainly originated from crystal grains at high temperature. The activation energy was calculated to be 1.37–1.44 eV from Arrhenius fitting results. After Sm³⁺ substitution, the activation energy for conductivity was increased as a result of reduced oxygen vacancies.     

Electrical behavior of the Ruddlesden–Popper phase, (Nd0.9La0.1)2 Ni0.75Cu0.25O4 (NLNC) and NLNC- x wt% Sm0.2Ce0.8O1.9 (SDC) (x = 10, 30 and 50), as intermediate‐temperature solid oxide fuel cells cathode

In the present work, a new Ruddlesden-Popper phase, (Nd_0.9La_0.1)₂ Ni_0.75Cu_0.25O₄ (NLNC) has been synthesized by solid state reaction for intermediate-temperature solid oxide fuel cells (IT-SOFCs) applications. The effect of sintering temperature on the microstructure and electrical properties of the NLNC cathode material is investigated. Likewise, composite cathode materials were also prepared by mixing the NLNC with 10, 30 and 50 wt% of Sm_0.2Ce_0.8O_1.9 (SDC) powders, and firing in the temperature range of 1000–1300 °C. The crystal structure and chemical compatibility of NLNC and SDC, and their microstructures were studied by XRD and SEM, respectively. Electrical conductivity and performance of monolithic and composite electrodes as a function of the electrode composition is investigated experimentally through four probe method and electrochemical impedance spectroscopy (EIS). The results proved that no reaction occur between NLNC and SDC compounds even at a temperature as high as 1300 °C. Maximum total electrical conductivity of 114.36 S cm^?1 at 500 °C is recorded for the pure NLNC material sintered at 1300 °C. The polarization resistance of pure NLNC cathode was 0.43 Ω cm² at 800 °C; the NLNC–SDC composite cathodes including 10, 30 and 50 wt% SDC displayed Rp value of 0.27 Ω cm², 0.11 Ω cm², and 0.19 Ω cm² at 800 °C, respectively.     

High temperature stable dielectric properties and enhanced energy-storage performance of (1− x)(0.85Na0.5Bi0.5TiO3 − 0.15Ba0.8Ca0.2Ti0.8Zr0.2O3)− xK0.5Na0.5NbO3 lead-free ceramics

Novel high temperature ceramic capacitors (1??x)(Na_0.5Bi_0.5TiO₃ ??0.15Ba_0.8Ca_0.2Ti_0.8Zr_0.2O₃)??xK_0.5Na_0.5NbO₃ were synthesized in the solid-state reaction route. The influence of K_0.5Na_0.5NbO₃ modification on dielectric behavior, energy-storage properties, ac impedance and temperature stable dielectric performance were systematically investigated. The reduced grain size and enhanced relaxor properties are obtained with the addition of KNN. The content of x?=?0.1 exhibits a stable permittivity (~ 1630) and dielectric loss (<?0.05) over a relatively broad temperature range (66–230?°C). A variation in permittivity within ±?15% can be observed over a pretty wide temperature range of 66–450?°C. Beyond that, this ceramic shows enhanced energy-storage properties with the density (W_rec) of 0.52?J/cm³ and efficiency (η) of 80.3% at 110?kV/cm. The possible contributions of the grain and the grain boundary to the ceramic capacitance are discussed by the ac impedance spectroscopy.     

A novel ((Bi0.5Na0.5)0.94Ba0.06)1-x (K0.5Nd0.5)xTiO3 lead-free relaxor ferroelectric ceramic with large electrostrains at wide temperature ranges

Novel ((Bi_0.5Na_0.5)_0.94Ba_0.06)_1-x(K_0.5Nd_0.5)_xTiO₃(x = 0.0, 0.02, 0.04, 0.06) lead-free ceramics (BNBT–xKN) were prepared by the solid-state reaction method. The effects of A-site (K_0.5Nd_0.5)²⁺ complex-ion substitution on their phase structure, dielectric, piezoelectric, and electromechanical properties were studied. The X-ray diffraction results indicate that all compositions are located in the morphotropic phase boundary (MPB) region where the tetragonal phase coexists with the rhombohedral phase. In addition, as the KN content increases, the ferroelectric order transform to relaxor order, which is characterized by a degeneration of maximum polarization, remnant polarization and correspondingly adjusts the ferroelectric-relaxor transformation temperature (T_F-R) to room temperature. Interestingly, the disruption of ferroelectric phase caused a significant improvement of strains. A maximum strain of ~ 0.52% corresponding to normalized strain of ~ 612 pm/V appeared at 85 kv/cm for the x = 0.04 composition. Particularly, the composition of x = 0.04 exhibited high electrostrains of temperature insensitivity, which remained above 0.4% and kept within 10% from ambient temperature up to 110 °C. It can be ascribed to the coexistence of non-ergodic and ergodic states in the relaxor region. As a result, the systematic investigations on the BNBT–xKN ceramics can benefit the developments of temperature-insensitive “on-off” actuators.     

Enhanced microstructure and electrical properties of Mn-modified Bi0.5(Na0.65K0.35)0.5TiO3 ferroelectric ceramics

Bi_0.5(Na_0.65K_0.35)_0.5TiO₃ (BNKT) and Mn-modified Bi_0.5(Na_0.65K_0.35)_0.5(Mn_xTi_1−x)O₃ (BNKMT-10³x), (x=0.0–0.5%) ferroelectric ceramics were synthesized by solid-state reaction method. Optimization of calcination temperature in Mn-doped ceramics was carried out for the removal of secondary phases observed in XRD analysis. BNKMT ceramics sintered at 1090 °C showed enhanced dielectric, piezoelectric and ferroelectric properties in comparison to pure BNKT. The average grain size was found to increase from 0.35 μm in BNKT to 0.52 μm in Bi_0.5(Na_0.65K_0.35)_0.5(Mn_0.0025Ti_0.9975)O₃ (BNKMT-2.5) ceramics. The dielectric permittivity maximum temperature (T_m) was increased to a maximum of 345 °C with Mn-modification. AC conductivity analysis was performed as a function of temperature and frequency to investigate the conduction behavior and determine activation energies. Significant high value of piezoelectric charge coefficient (d₃₃=176 pC/N) was achieved in BNKMT 2.5 ceramics. Improved temperature stability of ferroelectric behavior was observed in the temperature dependent P–E hysteresis loops as a result of Mn-incorporation. The fatigue free nature along with enhanced dielectric and ferroelectric properties make BNKMT-2.5 ceramic a promising candidate for replacing lead based ceramics in device applications.     

Effects of Tb doping on structural and electrical properties of 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 thin films at various annealing temperature by pulsed laser deposition

The ceramic thin films of 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + x (x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization (P_r) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm². Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10^?9?1.97 × 10^?8 A/cm² under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10^?7 A/cm²).     

Low-temperature sintering of Ti1−xCux/3Nb2x/3O2 (x = 0.23) microwave dielectric ceramics with CuO and B2O3 addition

The influence of CuO and B₂O₃ addition on the sintering behavior, microstructure and microwave dielectric properties of Ti_1?xCu_x/3Nb_2x/3O₂ (TCN, x = 0.23) ceramic have been investigated. It was found that the addition of CuO and B₂O₃ successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B₂O₃ has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B₂O₃ addition showed a high dielectric constant of 95.63, τ_f value of + 329 ppm/°C and a good Q × f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode.     

Investigation on the anti-reduction mechanism of Ti4+ in high dielectric constant system Ca0.9La0.067TiO3 by doping with Al2O3

Ca_0.9La_0.067TiO₃ (abbreviated as CLT) ceramics doped with different amount of Al₂O₃ were prepared via the solid state reaction method. The anti-reduction mechanism of Ti⁴⁺ in CLT ceramics was carefully investigated. X-ray diffraction (XRD) was used to analyze the phase composition and lattice structure. Meanwhile, the Rietveld method was taken to calculate the lattice parameters. X-ray photoelectron spectroscopy (XPS) was employed to study the valence variation of Ti ions in CLT ceramics without and with Al₂O₃. The results showed that Al³⁺ substituted for Ti⁴⁺ to form solid solution and the solid solubility limit of Al³⁺ is near 1.11 mol%. Furthermore, the reduction of Ti⁴⁺ in CLT ceramics was restrained by acceptor doping process and the Q × f values of CLT ceramics were improved significantly. The CLT ceramic doped with 1.11 mol% Al₂O₃ exhibited good microwave dielectric properties: ε_r = 141, Q × f = 6848 GHz, τ_f = 576 ppm/°C.     

Electrical relaxation and conduction mechanisms in iron doped barium strontium titanate

Polycrystalline Ba_0.7Sr_0.3Ti_(1?x)Fe_xO₃ (x = 0.1) (BSTF) ceramics, synthesized via solid-state reaction route were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance spectroscopy (CIS). The Rietveld refinement of the XRD data confirmed the presence of tetragonal and cubic phases in the prepared sample. The SEM image revealed that the sample has well distributed grains along with some degree of agglomerations. The electrical behaviour of the BSTF ceramic has been studied by complex impedance spectroscopy (CIS) as a function of frequency (1 Hz to 1 MHz) at different temperatures (RT to 700 K). Two semicircular arcs observed in the Cole-Cole plot confirm the contribution from the grain and grain boundary in overall impedance. Both the electrical as well as ac conduction phenomena take place via correlated barrier hopping (CBH) authenticated by detailed complex modulus analysis and ac fitted conductivity respectively. The values of activation energies calculated from electrical impedance, modulus, and conductivity data clearly reveal that the relaxation and conduction processes in BSTF ceramic are induced by doubly ionized oxygen vacancies.     

Colossal permittivity and impedance analysis of tantalum and samarium co-doped TiO2 ceramics

In this study, (Ta_0.5Sm_0.5)_xTi_1−xO₂ (x = 0, 0.02, 0.06, 0.15) ceramics (referred to as TSTO) were fabricated by a standard solid-state reaction. As revealed by the X-ray diffraction (XRD) spectra, the TSTOs exhibit a tetragonal rutile TiO₂ structure. All the TSTO ceramics display colossal permittivity (~ 10²–10⁵). Moreover, the optimal ceramic, (Ta_0.5Sm_0.5)_0.02Ti_0.98O₂, exhibits high performance over a wide temperature range from 20 °C to 160 °C. At 1 kHz, the dielectric constant and dielectric loss are 2.30 × 10⁴ and 0.11 at 20 °C; they are 3.85 × 10⁴ and 0.64 at 160 °C. Dielectric and impedance spectra analyses for the TSTO ceramics indicate that the CP behavior over a broad temperature range in (Ta+Sm) co-doped TiO₂ could be explained by the internal barrier layer capacitance (IBLC) model, which consists of semiconducting grains and insulating grain boundaries.     

Dielectric and optical properties of Ni doped Na0.5Bi0.5TiO3

Polycrystalline Ni doped Na_.5Bi_0.5TiO₃ samples (Na_0.5Bi_0.5)Ti_1-xNi_xO_3, (x?=?0.5, 0.10, 0.15) have been prepared by solid state reaction. The appearance of the additional peak in X-ray diffraction pattern indicates the ordering of Ti⁴⁺ and Ni²⁺ ions. Polygonal grains are converted into flakes with an increase of Ni concentration. Replacement of Ti⁴⁺ by Ni²⁺ strongly modifies the relative contribution of two peaks in the Raman bands within 200–400?cm^?1. Oxygen vacancy is observed in X-ray photoelectron spectrum to maintain charge neutrality due to aliovalent doping. Broad diffuse phase transition centered at the dielectric constant maximum indicates relaxor behaviour. Comparison between impedance and electric modulus spectrum suggests non-Debye relaxation. The ac conductivity follows the power law with the frequency exponent lies 0.52???0.72. The generation of holes by divalent Ni dopant at tetravalent Ti sites enhances optical band gap.     

Dielectric properties of Sr0.5Ca0.5TiO3: x Pr3+ ceramics

The frequency dependent dielectric and AC conductivity properties of different concentrations of Pr³⁺ doped Sr_0.5Ca_0.5TiO₃ ceramics were investigated for the frequency range 100 Hz to 2 MHz at different temperatures. The morphology of the prepared samples was analyzed by using Field-Emission Scanning Electron Microscope images. The value of dielectric constant and dielectric loss decreases with increase in the frequency of the applied signal in all the samples. Also, the value of dielectric constant and dielectric loss decreased with doping of different concentrations of Pr³⁺ ions. The conductivity of the samples obeys Jonscher's power-law and shows a decrease with increasing doping concentration of Pr³⁺ ions. The higher value of real and imaginary part of impedance at lower frequency indicates the space charge polarization of the material and its absence at higher frequencies was confirmed from the low value of impedance at higher frequency region. The Cole- Cole parameters of the samples were calculated and the semi-circle observed indicates a single relaxation process and can be modeled by an equivalent parallel RC circuit. At lower frequency region, the value of dielectric constant and dissipation factor increases with increase in the temperature. Also the value of conductivity increases with temperature at high frequency region, due to the enhanced mobility of charge carriers.     

Large electric-field-induced strain in B-site complex-ion (Fe0.5Nb0.5)4+-doped Bi1/2 (Na0.82K0.12)1/2TiO3 lead-free piezoceramics

In order to obtain a new system of (Bi_1/2Na_1/2)TiO₃ (BNT) based lead-free incipient piezoceramics with large strain for practical applications of actuators, we investigated the effect of B-site complex-ion (Fe_0.5Nb_0.5)⁴⁺ (FN)-doped Bi_1/2 (Na_0.82K_0.12)_1/2TiO₃ ceramics on the phase structure, dielectric, ferroelectric, piezoelectric and electric-field-induced strain properties. All samples exhibited single perovskite phase with pseudocubic symmetry. The room temperature electric-field-induced polarization (P-E) and strain (S-E) hysteresis loops indirectly illustrated ferroelectric-to-relaxor (FE-RE) phase transition. The increasing content of FN doping decreased the FE-RE phase transition temperature, T_F-R to below room temperature and induced the reversible FE-RE phase transition, giving rise to a large strain of 0.462% with a normalized strain, d^*₃₃ of 660 pm/V at a critical composition of x = 5. A fluctuation of the dielectric curve for BNKT-5 mol% FN ceramics in the spectra around 80 °C before and after polarization suggested that the large strain response can be induced via delicate mixing of the FE and RE phase.     

Microstructural and microwave dielectric properties of LZT (Li2ZnTi3O8) ceramics sintered in presence of bismuth borate glass for LTCC applications

In the present research, the Li₂ZnTi₃O₈(LZT) ceramics were synthesized throughout solid-state ceramic processing, then mixed with bismuth borate (BiBO) glass prepared based on conventional melt quenching method. Wetting behavior of BiBO glass on the LZT ceramic substrate was monitored by hot stage microscopy. Afterward, dielectric LZT ceramics containing different amounts of BiBO glass (0.25–6 wt%) were sintered at various temperatures. X-ray diffraction and electron back scatter diffraction examinations revealed the presence of two crystalline phases of Li₂ZnTi₃O₈ and Bi₂Ti₂O₇. The maximum value of relative density (above 95%) was obtained in the case of specimens contained more than 5 wt% glass. The microwave dielectric properties of the finally sintered BiBO glass containing LZT ceramics were as follows: dielectric constant (ε_r) = 21.44–25.09, quality factor (Q × f) = 10839–54708 GHz and temperature coefficient of resonant frequency (τ_f) = (? 15.58) ? (? 12.86)ppm/°C.     

Effects of zinc nitrate as a sintering aid on the electrochemical characteristics of Sr0.92Y0.08TiO3–δ and Sr0.92Y0.08Ti0.6Fe0.4O3–δ anodes

Although Sr_0.92Y_0.08TiO_3–δ (SYT) and Sr_0.92Y_0.08Ti_0.6Fe_0.4O_3–δ (SYTF) have been widely considered as promising materials for solid oxide fuel cell anodes, the poor densification restricts their commercial applications. As a sintering aid, zinc nitrate successfully stimulates the sintering process and improves densification. An investigation of linear shrinkage and scanning electron microscopy images indicated that the sinterability of SYT and SYTF materials was effectively improved by impregnating the green body with 5 mol% of Zn. It was found that the modification with zinc lowered the activation energy of the electrical conduction process and significantly improved the electrical conductivities of SYT and SYTF at all atmospheric conditions. The maximum power densities of the SYT and SYTF anodes were improved from 19.7 and 34.1 mW cm^–2 to 56.9 and 92.3 mW cm^–2 in H₂ and from 10.2 and 19.4 mW cm^–2 to 47.5 and 61.9 mW cm^–2 in CH₄, respectively.