Structural,dielectric and piezoelectric properties of xBiFeO3–(1−x)BaTi0.9Zr0.1O3 ceramics

Effect of BiFeO₃ (BFO) content on the microstructure and electrical properties of BaTi_0.9Zr_0.1O₃ (BTZ) ceramics prepared by the solid-state reaction technique was investigated. X-ray diffraction analyses show that BFO diffused into the lattice of BTZ to form a solid solution with perovskite structure. The relative density of the BTZ ceramics is increased by the introduction of BFO. The dielectric study reveals that the dielectric constant and the average dielectric loss of the solid solution decreased simultaneously with an increase in BFO content. The materials undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in BFO contents in the studied composition range. On the other hand, the piezoelectric coefficient and electromechanical coupling coefficient decrease simultaneously with increasing the BFO content, whereas the mechanical quality factor increases gradually. The structure–property relationship and the mechanism associated with the change of the electrical properties are discussed intensively.     

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.     

Sintering,micro-structure and Li+ conductivity of Li7−xLa3Zr2−xNbxO12/MgO (x = 0.2–0.7) Li-Garnet composite ceramics

Nb-doped Li₇La₃Zr₂O₁₂ (Nb-LLZO) is one of the promising electrolyte candidates in the Li-Garnet family due to its high Li-ion conductivity. The sintered Nb-LLZO ceramics, however, often exhibit abnormal grain growth with high porosity and poor mechanical properties. For advantaged electrochemical and mechanical properties, a uniform and dense microstructure is desired. In this research, MgO has been added as a secondary phase to inhibit abnormal grain growth in Nb-LLZO. The sintering process of the Nb-LLZO/MgO composite ceramics has been studied for different Nb doping levels (0.2–0.7 pfu) at sintering conditions of 1250?°C for 1–360?min. The ceramic density, microstructure, and Li-ion conductivity are reported. The composite ceramics have shown a very fast sintering speed. At 1250?°C, the 0.4Nb-LLZO/MgO composite can be well-sintered in 1?min. For sintering at 1250?°C for 40?min, ceramic samples showing relative density of 97%, conductivity of 6?×?10^?4 S?cm^?1 at 25?°C, and activation energy of 0.40?eV are obtained.     

Structural,dielectric, piezoelectric,ferroelectric and electro-caloric properties of Ba1−xCaxTi0.975(Nb0.5Yb0.5)0.025O3 lead-free ceramics

Polycrystalline samples of Ba_1?xCa_xTi_0.975(Nb_0.5Yb_0.5)_0.025O₃ (where x = 0.15, 0.2 and 0.3, abbreviated as BCTYN) were prepared by the conventional solid state reaction method. The effect of calcium (Ca) substitution in BaTi_0.975(Nb_0.5Yb_0.5)_0.025O₃ (abbreviated as BTYN25) on the structural, dielectric, piezoelectric and ferroelectric properties and electro-caloric effects (ECE) was investigated. X-ray diffraction (XRD) results at room temperature showed that the BCTYN samples in the composition x < 0.3 exhibited a pure tetragonal perovskite structure. Dielectric measurements showed a classical ferroelectric behavior for all samples. With the increase of the Ca content, the Curie temperature (T_C) was still maintained with a small shift towards low temperature. The evolution of the Raman spectra was studied as a function of compositions and temperatures. The Raman bands confirmed the structure and the phase transition of the BCTYN ceramics. By adding Ca, the piezoelectric properties and the remanent polarization (P_r) are relatively maintained for the compositions x = 0.15 and x = 0.2. A piezoelectric coefficient of d₃₃ = 130 pC/N and a planar electromechanical coupling factor of k_p = 28% were obtained for these compositions. Two different methods were used to calculate the electro-caloric coefficients of the BCTYN ceramics. The incorporation of Ca was found to enhance the electro-caloric strength (ξ = ΔT/ΔE) within a broad temperature range with a best value of ξ = 0.2?Kmm/kV for x = 0.2.     

Sol-gel synthesized and microwave heated Pb0.8-yLayCo0.2TiO3 (y = 0.2–0.8) nanoparticles: Structural,morphological and dielectric properties

In this work, the Pb_0.8-yLa_yCo_0.2TiO₃ (y?=?0.2–0.8) (PLCT) nanoparticles were prepared by sol-gel method and further subjected to microwave heating. The formed tetragonal reflection planes of PLCT samples were on par with PbTiO₃ (PT) and lanthanum cobalt titanate (LCT) tetragonal phases. Especially, for y?=?0.2–0.4, PLCT attained the PT structure while for y?=?0.6–0.8, PLCT acquired the LCT structure. That is, the structural transformation occurred from tetragonal PT to tetragonal LCT phases at higher La-contents. The high resolution transmission electron microscope (HRTEM) and field emission scanning electron microscopes (FESEM) showed complete formation of nanofibers at y?=?0.8 which may reveal drug delivery system applications. The Fourier transform infrared spectra (FTIR) were recorded in order to find the presence of metal oxide bonds. The dielectric properties evidenced that the transition temperatures (T_c) were found to be increasing from 713 to 783?K with increase of y-value. Furthermore, the temperature and frequency dependence of dielectric constant (ε′), dielectric loss (ε′′), ac-electrical conductivity (σ_ac), real (M′) and imaginary (M′′) parts of complex dielectric modulus (M*) was described. The Power law was used to fit the logσ_ac versus logω plots in order to determine the dc-conductivity (σ_dc) and exponent (n) values of the samples at room temperature (RT). Later on, the Arrhenius plots (lnσ_ac versus T^?1 plots) were drawn to find the activation energies. The results expressed the existence of two activation energies at low and high temperature regions due to slope change before and after T_c.     

Large strain of temperature insensitive in (1–x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO3) –xSr0.7La0.2TiO3 lead-free ceramics

Novel (1–x)(0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃)–xSr_0.7La_0.2TiO₃ ternary lead-free ceramics (BNBT–xSL, x?=?0.00–0.08) were fabricated by the widely used solid-state sintering technique. The crystal phase, microstructure, dielectric relaxation, piezoelectric, and electromechanical properties of each composition were systematically analyzed. It is found that the addition of SL has little effect on the crystal phase and grain morphology, but it can remarkably improved the relaxation property of the ceramic sample and gave rise to favourable dielectric properties in a wide range of temperatures. In addition, as the SL content increases, the ferroelectric to relaxor temperature (T_F-R) is adjusted to below ambient temperature. More importantly, the decay of ferroelectric phase resulted in a significant increase in strain value: the large strain of 0.5% with normalized strain of 625?pm/V was obtained at 80kv/cm and x?=?0.04. Finally, the composition exhibited high strain of temperature insensitivity range from room temperature to 100?°C, the strain value remained above 0.4% and kept within 5%. The results are due to the coexistence of rhombohedral polar-nanoregions (PNRs) and tetragonal PNRs during the relaxor region. This result is of great importance to the developments of temperature-insensitive strain sensors and actuators.     

Microwave-assisted sintering and improved dielectric,ferroelectric properties of 0.5[(Ba0.7Ca0.3)TiO3]–0.5[Ba(Zr0.2Ti0.8)O3] lead-free ceramics

0.5[(Ba_0.7Ca_0.3)TiO₃]–0.5[Ba(Zr_0.2Ti_0.8)O₃] lead-free ceramics were synthesised by coprecipitation method and sintered by fast microwave sintering (MWS) and by conventional sintering (CS) at 1200°C. After being sintered with the two different methods, the materials were characterised for structural, microstructural, frequency and temperature-dependent dielectric properties, Raman spectroscopy, and ferroelectric measurements. Results are compared and discussed in the present paper. X-ray diffraction confirms the presence of the tetragonal and rhombohedral phases in the composites sintered by both methods. The ferroelectric to paraelectric transition temperature (Tc) is increased in microwave-sintered composite. Diffuse constant (γ) values show BCT–BZT ceramics to be neither normal ferroelectrics nor relaxor ferroelectrics. Raman spectra confirm phase transition in the ceramic samples. Saturation polarisation (Ps) values are 7.62 and 4.28?µC?cm^?2 and nearly equal remanant polarisation (Pr) values were observed for BCT–BZT composite sintered with MWS and CS, respectively.     

Butyl rubber–Ba0.7Sr0.3TiO3 composites for flexible microwave electronic applications

Butyl rubber–Ba_0.7Sr_0.3TiO₃ composites (BR–BST) were prepared by sigma mixing followed by hot pressing. The stress–strain studies show the good flexibility of the composite. The dielectric properties of the composites were investigated at both radio and microwave frequencies. The relative permittivity (ε_r) and loss tangent (tan δ) improved with filler loading at both the frequencies. The relative permittivity and loss tangent of the BR–BST composites at a maximum filler loading of 0.39 volume fraction (v_f) are 13.1 and 0.009 respectively at 5 GHz measured by Split Post Dielectric Resonator (SPDR). The effective relative permittivity of the BR–BST composites is compared with theoretical models. The variation of ε_r with temperature was also investigated in the range 22–80 °C at 1 MHz. The microwave dielectric properties of the composites are also studied after repeated bending. The coefficient of thermal expansion (CTE) of the butyl rubber–BST composites decreased with the addition of the BST ceramic.     

Electrical characterization of BaTiO3 and Ba0.77Ca0.23TiO3 ceramics synthesized by the proteic sol–gel method

In this work, we introduce a simple, low-cost, and ecofriendly method for producing barium titanate (BaTiO₃–BT) and barium calcium titanate (Ba_0.77Ca_0.23TiO₃–BCT) powders. The synthesis was performed by using a proteic sol–gel route which use coconut water in the polymerization step of the metallic precursor. We investigated the effects of the processing parameters with the density, microstructure, and (di)electric properties as sample quality indicators. The sintered ceramics exhibit single crystalline phase, relative density of 95%, a homogeneous microstructure, and an average grain size of 4?µm. The respective dielectric constants of 1200 (BT) and 700 (BCT), measured at room temperature, and the activation energy values for the conductive process are according to those reported in the literature for conventionally prepared ceramics.     

Structural,optical and electrical properties of Ce0.8Sm0.2-xErxO2-δ (x = 0–0.2) Co-doped ceria electrolytes

This study examined the effects of samarium and erbium co-doping on the structural, optical, and electrical properties of ceria (CeO₂). Ceramic (Ce_0.8Sm_0.2-xEr_xO_2-δ; x?=?0, 0.05, 0.10, 0.15, 0.20) electrolytes were synthesized via sol-gel assisted citric acid–nitrate combustion and calcined at 850?°C for 5?h. The calcined electrolytes possessed a cubic fluorite crystal structure without impure phases. The direct band gap of the calcined electrolytes increased as the erbium content increased and the lowest band gap was obtained for Ce_0.8Sm_0.2O_2-δ (SDC) electrolyte. The calcined electrolyte powders were subsequently pressed into cylindrical pellets by uniaxial die pressing, and the pellets were sintered at 1400?°C for 5?h. The sintered densities of the pellets were measured with Archimedes’ method. The relative density of Ce_0.8Sm_0.1Er_0.1O_2-δ co-doped ceria electrolyte was higher than those of singly doped ones, and these findings were further confirmed through field emission scanning electron microscopy. Electrochemical impedance spectroscopy indicated that the conductivity of erbium-doped ceria increased as the samarium content increased. The maximum total ionic conductivity was observed in Ce_0.8Sm_0.1Er_0.1O_2-δ co-doped electrolyte. However, the singly doped SDC electrolyte exhibited the highest ionic conductivity of 13.12 mS/cm and the lowest activation energy of 0.580?eV at 600?°C among all other Ce_0.8Sm_0.2-xEr_xO_2-δ co-doped ceria electrolytes.     

Origin of superior dielectric and piezoelectric properties in 0.4Ba(Zr0.2Ti0.8)O3–0.6(Ba0.7Ca0.3)TiO3 at intermediate grain sizes

Grain size effect is one of the most important issues to develop next-generation multilayer microdevices. In this work, the tetragonal 0.4Ba(Zr_0.2Ti_0.8)O₃–0.6(Ba_0.7Ca_0.3)TiO₃ (BZT–60BCT) ceramics with a wide grain size from 2.1 to 24 μm were successfully prepared by using ultrafine nano powder and two-step sintering. The results demonstrate that critical/intermediate grain size of dielectric constant ε_r and piezoelectric constant d₃₃ appears at ∼12.9 μm. It was found that the presence of large lattice tetragonality, and enhanced domain wall motion induced by domain coexistence between submicron and nano size in sample with a grain size of ∼12.9 μm, resulting in the superior dielectric and piezoelectric properties. These findings and analyses of the origin of superior dielectric and piezoelectric properties at intermediate grain size have important practical implications in the design of high-performance piezoelectric ceramics.     

Crystal structure and temperature dependent structural phase transitions in (Ba1-xSrx)PbO3 (x = 0, 0.2, 0.6) perovskite ceramics

The structural properties of (Ba_1-xSr_x)PbO₃ (x?=?0, 0.2 and 0.6) ceramics were examined in a wide range of temperatures, from 14?K to 1223?K, using the X-ray powder diffraction method. The type of distortion of the pseudo-cubic perovskite cell was determined from the splitting of the main diffraction lines and from the analysis of the superlattice peaks. Temperature-induced structural phase transitions at high temperatures were observed. On the other hand at temperatures starting as low as 14?K, the examined ceramics did not show any phase transitions. The effect of Sr doping was evaluated and showed that with an increase in the amount of Sr²⁺ ions in the crystal lattice the number of SPT's decreases. Additionally, the temperatures at which these SPT's occur are shifted towards higher values. The following sequences of structural phase transitions, written using Glazer's notation, were proposed:I2/m (a^-b⁰c^-) → Ibmm (a^-b⁰a^-)→ I4/mcm (a⁰a⁰c^-)→ $Pm\overline{3}m$(a⁰a⁰a⁰) for BaPbO₃I2/m (a^-b⁰c^-) → I4/mcm (a⁰a⁰c^-) → $Pm\overline{3}m$(a⁰a⁰a⁰) for (Ba_0.8Sr_0.2)PbO₃and I2/m (a^-b⁰c^-)→ I4/mcm (a⁰a⁰c^-)→ $Pm\overline{3}m$(a⁰a⁰a⁰) for (Ba_0.4Sr_0.6)PbO₃.These SPT's were used as trial models in refinement procedures based on the Rietveld method.     

Dielectric,ferroelectric, magnetic and magnetoelectric properties of 0.1Ni0.8Zn0.2Fe2O4–0.9Pb1−3x/2SmxZr0.65Ti0.35O3 magnetoelectric composites

Composites having general formula 0.1Ni_0.8Zn_0.2Fe₂O₄–0.9Pb_1−3x/2Sm_xZr_0.65Ti_0.35O₃ with x=0, 0.01, 0.02 and 0.03 were synthesized by a conventional solid state reaction route. X-ray diffraction analysis was carried out to confirm the coexistence of individual phases and microstructural study was done by using a scanning electron microscope. Dielectric properties were studied as a function of temperature and frequency. To study ferroelectric and magnetic ordering in composite samples, P–E and M–H hysteresis loops were recorded respectively. Maximum magnetoelectric coupling coefficient of 22.5 mV/cm Oe was observed for sample with x=0.03. A significant improvement in dielectric, ferroelectric, piezoelectric and magnetoelectric properties was observed for Sm substitution.     

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).     

Electrocaloric effect based on the depolarization transition in (1−x)Bi0.5Na0.5TiO3–xKNbO3 lead-free ceramics

Lead-free ferroelectric ceramics (1−x)Bi_0.5Na_0.5TiO₃−xKNbO₃ (BNT–xKN) with x=0.00, 0.04, 0.06 and 0.08 were synthesized by the conventional solid state reaction method. The effects of the KNbO₃ addition on the dielectric behavior, ferroelectric properties, as well as electrocaloric effect of the ferroelectric ceramic BNT–xKN were investigated. The results show that the depolarization temperature decreases with the increment of KN content. A high ECE of 1.73 °C is achieved at 76 °C in BNT–0.06KN. The relation between electrocaloric effect and depolarization transition was discussed. This investigation indicates that the depolarization transition below Curie transition in BNT-based ceramics is a promising approach in ECE technique.     

Phase structure,piezoelectric, ferroelectric,and electric-field-induced strain properties of Nb-modified 0.8Bi0.5Na0.5TiO3−0.2Sr0.85Bi0.1TiO3 ceramics

0.8Bi_0.5Na_0.5Ti_(1-x)Nb_xO₃−0.2Sr_0.85Bi_0.1TiO₃ (BNT-SBT-xNb, x = 0.00, 0.01, 0.02, and 0.03) piezoelectric ceramics were prepared by traditional solid state reaction and the influence of Nb substitution on the phase structure, ferroelectric, piezoelectric, and electric-field-induced strain properties in BNT-SBT ceramics were studied. XRD results exhibited that Nb⁵⁺ ions could fully diffuse into BNT-SBT structure to form a solid solution when x = 0.01. P-E loops and S-E curves suggested that the ferroelectric phase transformed to ergodic relaxor state (FE-to-ER) with the increasing the amount of Nb additive, indicating the ferroelectric long-ranged order was disturbed by the excess of Nb. With increasing Nb doping, phase transition temperature from normal ferroelectric to ergodic relaxor (short for T_F-R) could be reduced from 120 °C to 40 °C. Furthermore, for sample with x = 0.01, the normalized strain d₃₃^* got a maximum value ~571 pm/V due to the phase transition from ergodic relaxor to ferroelectric (ER-to-FE) under electric field.     

Improvement of dielectric breakdown strength and energy storage performance in Er2O3–modified 0.95Sr0.7Ba0.3Nb2O6-0.05CaTiO3 lead-free ceramics

In this study, 0.95?Sr_0.7Ba_0.3Nb₂O₆-0.05CaTiO₃-x wt% Er₂O₃ ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr_0.7Ba_0.3Nb₂O₆-0.05CaTiO₃ ceramics, the Er₂O₃ dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm³ and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors.     

Structure and electrical properties of Nd2O3-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 ceramics

Nd₂O₃ doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (abbreviated to BNKT) binary lead-free piezoelectric ceramics were synthesized by the conventional mixed-oxide method. The results show that the BNKT ceramics with 0–0.15 wt.% Nd₂O₃ doping possesses a single perovskite phase with rhombohedral structure. The grain size of BNKT decreased with the addition of Nd₂O₃ dopant. The temperature dependence of the dielectric constant ?_r revealed that there were two-phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. A diffuse character was proved by linear fitting of the modified Curie–Weiss law. At room temperature, the specimens containing 0.0125 wt.% Nd₂O₃ with homogeneous microstructure presented excellent electrical properties: the piezoelectric constant d₃₃ = 134 pC/N, the electromechanical coupling factor K_p = 0.27, and the dielectric constant ?_r = 925 (1 kHz).