The effects of sintering temperature and content of x on phase formation,microstructure and dielectric properties of (1−x)(Bi0.4871Na0.4871La0.0172TiO3)−x(BaZr0.05Ti0.95O3) ceramics prepared via the combustion technique

(1?x)(Bi_0.4871Na_0.4871La_0.0172TiO₃)?x(BaZr_0.05Ti_0.95O₃) ceramics (abbreviated (1?x)BNLT?xBZT) where 0.1≤x≤0.3 were fabricated by the combustion technique using glycine as fuel. BNLT and BZT powders were calcined at temperatures of 825 °C for 4 h and 925 °C for 6 h, respectively. After that they were mixed with the different compositions. It was found that the optimum sintering temperature of (1?x)BNLT?xBZT ceramic was obtained at 1125 °C for 2 h. This ceramic had the highest density. The structure of the (1?x)BNLT?xBZT ceramics exhibited the co-existence of tetragonal and rhombohedral phases with x≤0.1. The tetragonality increases with the increase of x content. The average grain size, the density and the Curie temperatures decrease with increasing x content. The maximum dielectric constant and the highest P_r were at about 4850 and 12.7 μC/cm², respectively, and were obtained by the 0.85BNLT?0.15BZT sample.     

Effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 lead-free ferroelectric ceramics

The effect of CuO addition on magnetic and electrical properties of Sr₂Bi₄Ti₅O₁₈ (SBT) lead-free bismuth layered structure ferroelectric ceramics have been studied and reported. Interestingly, the prepared samples exhibit multiferroic behavior with the coexistence of magnetic and ferroelectric phase transition temperature. Magnetic phase transition with Neel׳s temperature (T_N) of 657 K is observed at 0.75 mol% of CuO added SBT ceramics, which is higher than the well known multiferroic BiFeO₃ (643 K) and the ferroelectric phase transition with Curie temperature (T_C) of 587 K is observed at 1 mol% of CuO added SBT ceramics, which is relatively higher than the reported pure SBT ceramics (558 K). Further, the electrical properties such as dielectric, ferroelectric, piezoelectric, leakage current density characteristics and optical properties were investigated as a function of x (x=0, 0.25, 0.5, 0.75 and 1 mol%). Presence of strong magnetic super-exchange interactions in CuO and the creation of oxygen vacancies play a vital role in the enhancement of magnetic and electrical properties of CuO doped SBT ceramics. Moreover, the present results indicate that, small amount (0.25 mol%) of CuO addition in SBT ceramics enhances the electrical properties significantly and vice versa, large amount (0.75 mol%) of CuO addition enhances the magnetic properties. Thus, the presence of magneto-electric coupling effect was observed in CuO doped Sr₂Bi₄Ti₅O₁₈ ferroelectric ceramics.     

The relationship between the micro-mechanism and macroscopic dielectric properties in Ba1−xBixTi1−x−yZn0.75xW0.25x+yO3+y systems

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO₃ ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε_r, dielectric stability and dielectric loss) in Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10¹² Ω cm. These features suggested that the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment.     

Microwave dielectric properties of BaO–Ta2O5–TiO2 system

Microwave dielectric properties of the BaO–Ta₂O₅–TiO₂ system were investigated by the solid-state reaction method. It was recognized that the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions have the higher Q · f value in comparison with the Ba₈(Ta_4 − xNb_x)Ti₃O₂₄ solid solutions. The limit of the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions was approximately x = 0.75; the lattice parameter c of the solid solutions, which is related to the change in the B(1)O₆ octahedron, was significantly increased in the composition range from 0 to 0.75. The Q · f values of the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions are remarkably improved by the Sn substitution for Ti; the highest Q · f value of 59,100 GHz is obtained at x = 0.75. Moreover, the ɛ_r and τ_f values of the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions at x = 0.75 were 25.6 and 30.3 ppm/°C, respectively.     

Property improvement of 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.04(ZrxTi1−x)0.99O3 ceramics by hot-pressing

The piezoelectric ceramics of the compositions expressed by the formula: 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb_0.96La_0.04(Zr_xTi_1−x)_0.99O₃ (x = 0.50–0.53) were prepared by two kind of sintering processes: conventional sintering (CS) and hot-pressing (HP) sintering. By comparing the properties of these two series of ceramics, piezoelectric coefficients (d₃₃), electromechanical coupling factors (k_p), dielectric constants (ɛ_r), etc. were enormously improved by HP sinter procedure, which can be attributed to the highly dense microstructure (bulk density >99%). The most impressive results are the d₃₃ (845pC/N) and k_p (0.703) in the HP specimen with Zr/Ti = 51/49, which have not been observed in the previous relative reports. Additionally, according to the contrast of the experiment data, the origin of the property improvement was analyzed in details.     

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.     

Microstructure and electrical properties of (Ba0.85Ca0.15)1−xLix(Ti0.90Zr0.10)1−xNbxO3 ceramics with a low dielectric loss and a low sintering temperature

A low sintering temperature is demonstrated for (Ba_0.85Ca_0.15)_1?xLi_x(Ti_0.90Zr_0.10)_1?xNb_xO₃ (BCLTZN-x) piezoelectric ceramics, where BCLTZN-x lead-free piezoelectric ceramics were prepared by the normal sintering. Effects of Li and Nb on the microstructure and electrical properties of these ceramics were investigated. The sintering temperature of BCLTZN-x ceramics was decreased greatly by introducing Li and Nb, and the grain size of these ceramics decreases with increasing x. These ceramics with a small amount of Li and Nb maintain good piezoelectric properties, together with a low sintering temperature and a lower dielectric loss. These ceramics with x = 0.01 demonstrate optimum electrical properties: d₃₃ ～ 353 pC/N, k_p ～ 41.1%, T_c ～ 86 °C, ?_r ～ 4236, and tan δ ～ 0.75%.     

Large-strain 0.7Pb(ZrxTi1−x)O3–0.1Pb(Zn1/3Nb2/3)O3–0.2Pb(Ni1/3Nb2/3)O3 piezoelectric ceramics for high-temperature application

0.7Pb(Zr_xTi_1−x)O₃–0.1Pb(Zn_1/3Nb_2/3)O₃–0.2Pb(Ni_1/3Nb_2/3)O₃ (0.7PZT–0.1PZN–0.2PNN, x = 0.44–0.47) piezoelectric powders and ceramics have been prepared through conventional solid-state reaction method. Outstanding piezoelectric and dielectric properties occurred at the morphotropic phase boundary (MPB), which was characterized by the X-ray diffraction spectrum. The MPB composition (x = 0.46) performed high d₃₃ value (641 pC/N), indicating that the system suited large-strain application. The field-induced strain reached 0.25% under a considerably low electric field (0.8 kV/mm) according to the bipolar strain *S–E loops. The effect of the grain size on the aging phenomenon and temperature stability has also been investigated. Due to higher Curie temperature and smaller grain size, the 0.7PZT–0.1PZN–0.2PNN ceramics maintained a high d₃₃ level after depoling treatment, revealing a superior strain capacity for high-temperature application.     

Electric-field-induced phase transition and large strain in lead-free Nb-doped BNKT-BST ceramics

A suite of Nb-based piezoelectric ceramics of 0.99[Bi_0.5(Na_0.4K_0.1)(Ti_1−xNb_x)]O₃–0.01(Ba_0.7Sr_0.3)TiO₃(BNKTN-BST), with x ranging from 0 to 0.030, was prepared by a conventional solid-state reaction method. X-ray diffraction patterns confirmed a single perovskite phase and the tetragonality was found to decrease with increasing Nb ratio. The BNKTN-BST ceramic had a high field-induced normalized strain coefficient of 634 pm/V at 2 mol% Nb content with a relatively small hysteresis compared with existing lead-free Bi-perovskite ceramics. An electric-field-dependent X-ray study was conducted to identify the main source of the high strain and ascertain the effect of electric fields on the crystal structure. The temperature-dependent P − E hysteresis loops of the BNKTN-BST ceramics were measured under an electric field of 60 kV/cm at various temperatures, and the effect of temperature on the ferroelectricity is discussed.     

Effects of Li2CO3 and Sm2O3 additives on low-temperature sintering and piezoelectric properties of PZN-PZT ceramics

To assist the development of applications for multilayer piezoelectric devices, the low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ with Li₂CO₃ and Sm₂O₃ additives were fabricated by a conventional solid-state reaction, and their structural and piezoelectric properties were studied. With the addition of Li₂CO₃, the minimum sintering temperature of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramics was reduced from 1125 °C to 950 °C through the formation of a liquid phase and its piezoelectric properties showed almost no degradation. When the sintering temperature was below 950 °C, however, the piezoelectric properties degraded obviously. The additional Sm₂O₃ resulted in a significant improvement in the piezoelectric properties of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ ceramic with added Li₂CO₃. When sintered at 900 °C, the optimized properties of the 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramic with 0.3 wt% Li₂CO₃ and 0.3 wt% Sm₂O₃ were obtained as d₃₃ = 483 pC/N, k₃₁ = 0.376, Q_m = 73, ɛ_r = 2524, tan δ = 0.0178.     

The effect of Nb doping on dielectric and ferroelectric properties of PZT thin films prepared by solution deposition

Niobium (Nb)-doped lead zirconate titanate thin films (PNZT) were produced by solution deposition with nominal compositions, Pb_(1?0.5x)(Zr_0.53Ti_0.47)_1?xNb_xO₃ where x = 0.00–0.07. The effects of sintering temperature, sintering time, variation of thickness in the films and change of niobium content were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. The best results were obtained in double-layered films (390 nm) sintered at 600 °C for 1 h. Optimum doping level was found in 1% Nb-doped films. For 1% Nb-doped [Pb_0.995(Zr_0.53Ti_0.47)_0.99Nb_0.01O₃] films, remanent polarization (P_r) of 35.8 μC/cm² and coercive field (E_c) of 75.7 kV/cm have been obtained. The maximum dielectric constant was achieved in 1% Nb-doped films which was 689. Ferroelectric and dielectric properties decreased at higher Nb doping levels because of the changes in the grain size and perovskite lattice parameters.     

Thermoelectric properties of Fe2(Ti1−xNbx)O5 pseudobrookite ceramics with low thermal conductivity

Fe₂(Ti_1-xNb_x)O₅ (x = 0, 0.005, 0.01, 0.02, 0.05) pseudobrookite with high relative densities have been prepared by solid state reaction and conventional sintering. The solubility of Nb in Fe₂TiO₅ is low, in between x = 0.01 and 0.02. Introducing Nb into Fe₂TiO₅ within the solubility limit improves the electrical conductivity and decreases the absolute value of the Seebeck coefficient. Small polaron hopping model is applied to explain the electrical conduction of Fe₂(Ti_1-xNb_x)O₅, as verified by the linear fit of the electrical conductivity and the temperature independent Seebeck coefficient above approximately 600 K. All compositions show low thermal conductivity, about 1–1.5 Wm⁻¹K⁻¹ from 673 K to 1000 K. It is found that similar ZT value (∼ 0.006) is obtained for Fe₂(Ti_1−xNb_x)O₅ with x = 0.01 and 0.02 at 1000 K.     

Processing and enhanced electrical properties of Sr1-x(K0.5Bi0.5)xBi2Nb2O9 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics, Sr_1−x(K_0.5Bi_0.5)_xBi₂Nb₂O₉ (SKBN-x, x=0, 0.2, 0.5, 1.0), were synthesized by a conventional solid-state reaction. Structural and electrical properties of SKBN-x ceramics were investigated. X-ray diffraction analysis suggested that the substitution led to the formation of a layered perovskite structure. Plate-like morphologies for the grains were clearly observed in all the samples, which are characteristic for layer-structure Aurivillius compounds. The Curie temperature (T_c) is found to shift to higher temperature from 445 °C to 509 °C with increasing (K, Bi) content. Excellent remanent polarization (2P_r∼15 μC/cm²) were obtained for SKBN-0.2 ceramic. High piezoelectric coefficient of d₃₃∼21  pC/N were obtained for the samples at x=0.5. Additionally, thermal annealing studies indicated that the piezoelectric coefficient (d₃₃) of SKBN-0.5 was unchanged even if annealing temperature increased to be 450 °C, demonstrating the ceramics are the promising candidates for high-temperature applications.     

Creating adjoining polymorphic phase transition (PPT) regions in ferroelectric (Ba,Sr)(Zr,Ti)O3 ceramics

In this work, we report the polymorphic phase transitions(PPT) in ferroelectric Ba_0.95Sr_0.05Zr_xTi_(1-x)O₃ (BSZT, x = 0.01–0.10) ceramics synthesized by using a solid-state reaction method. The doping elements and composition ratios were selected to create adjoining PPT phase boundaries near room temperature, hence to achieve a broadened peak of piezoelectric performance with respect to composition. The temperature-composition phase diagram was constructed and the effects of PPT on the electromechanical and ferroelectric properties of the ceramics were investigated. It was revealed that the two adjacent PPT regions at room temperature showed different characteristics in property enhancement. However, due to the proximity of the phase boundaries, Ba_0.95Sr_0.05Zr_xTi_(1-x)O₃ ceramics in a fairly broad range of compositions (0.02 ≤ x ≤ 0.07) showed excellent piezoelectric properties, including a large piezoelectric constant (312 pC/N ≤ d₃₃ ≤ 365 pC/N) and a high electromechanical coupling coefficient k_p (0.42 ≤ k_p ≤ 0.49).     

Crystal structure and piezoelectric properties of xPb(Mn1/3Nb2/3)O3–(0.2 − x)Pb(Zn1/3Nb2/3)O3–0.8Pb(Zr0.52Ti0.48)O3 ceramics

Pb(Mn_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (designated as PMnN–PZN–PZT) piezoelectric ceramics were prepared and the effects of PMnN content on the crystal structure and electrical properties were investigated. The results show that the pure perovskite phase forms in these ceramics. The crystal structure changes from tetragonal to rhombohedral and the lattice constant decreases with increase of PMnN content. The morphotropic phase boundary (MPB) of xPMnN–(0.2 ? x)PZN–0.8PZT ceramics occurs where the content of PMnN, x, lies between 0.05 and 0.085 mol. The dielectric constant (?), piezoelectric constant (d₃₃) and Curie temperature (T_c) decrease, while the mechanical quality factor (Q_m) increases with the increase of PMnN content. The ceramic with composition 0.075PMnN–0.125PZN–0.8PZT has the optimal piezoelectric properties, ? is 842, d₃₃ is 215 pC/N, T_c is 320 °C, k_p is 0.57 and Q_m amounts to 1020, which makes it a promising material for high power piezoelectric devices.     

Enhanced energy-storage performance of 0.94NBT-0.06BT thin films induced by a Pb0.8La0.1Ca0.1Ti0.975O3 seed layer

0.94(Na_0.5Bi_0.5TiO₃)-0.06BaTiO₃ ferroelectric thin films with and without the Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ seed layer were deposited on platinum-buffered silicon substrates by using Sol–Gel process. The influence of Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ seed layer and annealing temperatures on the microstructures, ferroelectric properties and energy-storage performances of the as-prepared films were investigated in details. The low annealing temperature and Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ seed layer could improve the values of electric break-down field strength and P_max-P_r, which play a vital role for high recoverable energy-storage density. Owing to the high electric break-down field strength value of 3310 kV/cm, a large recoverable energy density of W=17.2 J/cm³ and a high energy efficiency of η=74.3% were obtained for the 0.94(Na_0.5Bi_0.5TiO₃)-0.06BaTiO₃ thin film with the Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ seed layer, which was annealed at 450 °C.     

Composition-driven phase boundary and its energy harvesting performance of BCZT lead–free piezoelectric ceramic

Piezoelectric energy harvesting is a hot topic in the field of new energy, and the key point is to design high power lead-free piezoelectric ceramic. In this work, a novel lead–free material system of (1–x)Ba(Zr_0.1985Cu_0.0015Ti_0.8)O_3-δ–x(Ba_0.7Ca_0.3)TiO₃ [(1–x)BZCT–xBCT] was designed, and the energy harvesting characteristics were tailored through the composition-driven phase boundary evolution. The R–O–T phase boundary boosts the strong piezoelectric activity, obtaining an optimal energy harvesting performance. In the mode of the cantilever-type energy harvester, a high output power of 70 μW and voltage of 8 V were obtained at x = 0.55 specimen with a low resonance frequency of 90 Hz and acceleration of 10 m/s², which were further increased to 700 μW and 25 V when the acceleration increased to 50 m/s². The excellent low frequency characteristics show the potential applications of this material in piezoelectric generators harvesting environmental vibration energy.     

Investigation of dielectric and piezoelectric properties in Pb(Ni1/3Nb2/3)O3–PbHfO3–PbTiO3 ternary system

The dielectric and piezoelectric properties were investigated in the (1 ? x)Pb(Hf_1?yTi_y)O₃–xPb(Ni_1/3Nb_2/3)O₃ (PNN–PHT, x = 0.05–0.50, y = 0.55–0.70) ternary system. The morphotropic phase boundary (MPB) was determined by X-ray powder diffraction analysis. Isothermal map of Curie temperature (T_C) related to the compositions in the phase diagram was obtained. The optimum dielectric and piezoelectric properties were achieved in ceramics with the MPB compositions, with the maxima values being on the order of 6000 and 970pC/N, respectively. Rayleigh analysis was used to study the extrinsic contribution (domain wall motion) in PNN–PHT system, where the extrinsic contribution was found to be ～30% for composition 0.49PNN–0.51PHT(30/70), showing a high nonlinearity.     

Influence of Ca substitution on microstructure and electrical properties of Ba(Zr,Ti)O3 ceramics

In the present work, lead-free (Ba_1?xCa_x)(Zr_0.04Ti_0.96)O₃ (x=0.00–0.09) ceramics were fabricated via a solid-state reaction method. The microstructure and electrical properties of the ceramics were investigated. The microstructure of the BCZT ceramics showed a core shell structure at compositions of x=0.03 and 0.06. The substitution of small amount of Ba²⁺ by Ca²⁺ resulted in an improvement of the piezoelectric, dielectric and ferroelectric properties of the ceramics. The orthorhombic–tetragonal phase transition was found in the composition of x≤0.03. Piezoelectric coefficient of d₃₃～392 pC/N and lowest E_c～3.3 kV/cm with highest P_r～14.1 μC/cm² were obtained for the composition of x=0.03 while its Curie temperature (T_C) was as high as 125 °C. However, the ferroelectric to paraelectric transition temperature had slightly shifted towards room temperature with increasing Ca²⁺ concentration.     

Structure versus relaxor properties in Aurivillius type compounds

Structure refinements in M^IIBi₄Ti₄O₁₅ (M^II = Ca, Ba), Bi_4−xBa_xTi_3−xNb_xO₁₂, (Na_0.5Bi_0.5)_1−xBa_xBi₄Ti₄O₁₅ and Bi₄Ti₃O₁₂–PbTiO₃ systems are used to report structural features of relaxor Aurivillius phases. In compounds with relaxor-like behaviour, the average structure is almost undistorted, closed to the archetypal HT paraelectric phase, with a tolerance factor ≳0.996. The coordination number of Bi³⁺ in fluorite layers changes from {4 + 2} for ferroelectrics to {4} for relaxors. Transmission Electron Microscopy reveals some characteristic features of relaxors such as micro-twinning, shearing-type defects which attest from the existence of a compositional inhomogeneity and a disorder at a local scale.