Lead-free Ba0 Research Articles

Effect of La-doping on dielectric properties and energy storage density of lead-free Ba(Ti[formula omitted]Sn[formula omitted])O[formula omitted] ceramics

Lead-free Ba1–zLazTi0.95Sn0.05O3 with z=0.00, 0.015, 0.025, and 0.035 samples were prepared using solid-state reaction route. X-ray diffraction measurement reveals the single phase formation of ceramic samples. Scanning electron microscopy shows the inhibited grain growth (≤0.5 μm) at low La-doping while the higher La-doping in BTS ceramics yielded the larger grain size (2.5 μm). Raman spectra indicate the substitution of La at Ba site sublattice. Dielectric properties improved with La-doping in BTS ceramic samples. 3.5LBTS sample exhibits energy storage density as high as (Jd) ∼ 0.492 J/cm3 with an energy efficiency of 63% at ∼40 kV/cm, which is 5.5 times more than that of pure BTS ceramics. Such significant increment in energy storage density could be attributed to reduced grain size due to La-doping. Thus, the selected composition could be a new method for enhancing the energy storage density for device applications.

Effect of solution concentration on low-temperature synthesis of BCZT powders by sol–gel-hydrothermal method

Lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powders were successfully synthesized by sol–gel-hydrothermal method. The effect of NaOH concentration on microstructure and phase composition of BCZT powders was studied. The results of XRD, SEM, TEM, FTIR, and EDS showed that the synthesis temperature of BCZT powders could be decreased to a low temperature of 180 °C, which was about 1150 °C lower when compared with solid-state reaction and 800 °C lower when compared with sol–gel methods respectively. The NaOH concentration exerted a great effect on the structure of BCZT powders, as well as the average particle size. When the NaOH concentration was 8 M, BCZT powders had a cubic phase perovskite structure with a homogeneous composition, and the average particle size was about 60 nm. The BCZT ceramics followed by sintering had dense structure and excellent electrical properties (2Pr = 24.62 μC/cm2, 2Ec = 3.24 kV/cm, d33 = 488 pC/N). The significant properties could be attributed to the high activity of powders synthesized by sol–gel-hydrothermal method. The present study may provide a new method for low-temperature synthesis of lead-free piezoelectric powders with fine phase, microscopic morphology, and high activity.

Structural and electrical properties of lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramic

Lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic has been prepared by solgel synthesis method. The effect of sintering temperature on the structure of BCZT ceramic was investigated. X-ray Diffraction studies show the suppression of secondary phase TiO2 with an increase in sintering temperature. The formation oftetragonal-orthorhombic morphotropic phase boundary is observed at the sintering temperature of 1350 °C. Polarization (P) versus electric field (E) measurementshows a remnant polarization of 1.32 µC/cm2 and coercive field of 4.33 kV/cm.

Synthesis and electrical properties of lead-free piezo electrics for magnetoelectric applications

The Lead-free piezoelectric polycrystalline materials, BaTiO3 (BTO) and Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic are prepared by sol-gel synthesis method. The synthesis dynamics and the effect of sintering temperature on the purity and the formation of morphotropic phase boundaries in these samples are investigated. X-ray Diffraction studies show the cubic phase for the BTO at low temperature, whereas it transforms into the tetragonal for high-temperature synthesis. The BCZT exists in the mixed phases of tetragonal and orthorhombic structures. Formation of MPBs in BCZT are observed for the sintering temperature above 1350 °C. Polarization (P) versus electric field (E) measurement shows enhanced polarization values for the BCZT in comparison to the BTO.

Two-Step Poling for Improved Piezoelectric Properties in Lead-Free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 Ceramic System

Pb-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 piezoelectric nanopowder was synthesized by solid-state reaction method. Piezoelectric properties were improved by two different approaches by optimizing poling conditions. Results indicate that poling near polymorphic phase boundary leads to the minimization of conduction current. However, low degree of poling observed indicates poor piezoelectricity. On the contrary, with Two-Step poling method, where the sample was sequentially subjected to low bias field at high temperature (step-1) and high bias field at low temperature (step-2), improved the piezoelectricity. Further, enhanced piezoelectric properties were obtained with optimized bias field of 1.25 kV/mm for step-1 with improved domain alignment.

Particle-size-induced high piezoelectricity in (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 piezoceramics prepared from nanopowders

Lead-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 (BCST) ceramics were synthesized by solid-state reaction method at 1450 °C. High-energy ball mill was used to yield nanopowders with milling time ranging from 5 to 30 h at 175 rpm. TEM images depict the drop of average particle size from 163 to 10 nm with rising milling time. Formation of pure perovskite structure with structural changes resulting from varying particle size was confirmed using XRD. SEM micrographs reveal significant grain growth which peaks at 13.63 μm for the 25-h milled sample. Dielectric studies indicate that the Curie temperature (Tc) remains unaffected with milling time. Piezoelectric charge coefficient (d33), remnant polarization (Pr), field-induced strain (S%) and converse piezoelectric coefficient (d33*) upsurge with rising milling time with their peak values of 5 μC/cm2, 220 pC/N, 0.209% and 650 p.m./V respectively for this ceramic sample. Hydrostatic electrostrictive coefficient (Qh) remains high at 0.041 ± 0.003 m4C-2, which is even higher than some of the commonly used lead-based materials.

Frequency and temperature dependent dielectric properties in the lead free Ba0.75Ce0.033Sr0.2Ti0.96Sn0.04O3 ceramics

Ba0.75Ce0.033Sr0.2Ti0.96Sn0.04O3 ceramic was prepared by solid-state route. X-ray diffraction (XRD) analysis of the compound shows a tetragonal phase with the space group of P4mm at room temperature. The imaginary part of the impedance (Z″) as a function of frequency reveals the presence of relaxation phenomena. Nyquist plots of impedance exhibit a semicircle arcs at different temperatures and an electrical equivalent circuit of (R1//CPE1) − (R2//CPE2) has been purposed to describe the impedance results. The imaginary part of the complex permittivity ( $$\varepsilon^{\prime\prime}$$ ) and the dielectric factor (tan δ) show a drastic decrease with the frequency. The decrease can be interpreted by the polarization type of Maxwell–Wagner. On the basis of the universal power law of Jonscher, the conductivity can be written as: $$\sigma = \sigma_{{{\text{DC}}}} + A\omega^{n}$$ . At low frequencies, the conduction mechanism obeys to SPH model and to the CBH model at high frequencies.

High tunability in lead-free Ba0.85Sr0.15TiO3thick films for microwave tunable applications

Lead free ferroelectric Ba0.85Sr0.15TiO3(BST) thick films were successfully deposited by screen printing process on Ag–Pd/Al2O3 substrates. The microstructure of the samples was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The thick films showed a good adhesion to the Ag–Pd/Al2O3 substrate, a porous microstructure and uniform thicknessesof about 10 μm. The dielectric properties of BST thick films were studied over a wide frequency range (10-1 Hz to 106 Hz) and in a large temperature range from 25 °C to 350 °C. The AC conductivity in BST thick films was systematically investigated. Ferroelectric characterizations and tunability were also studied at room temperature by polarization cycles P(E) and capacitance C(E) measurements. The high values of dielectric permittivity and tunability (67%) combined with low dielectric loss (tgδ) make Ba0.85Sr0.15TiO3 thick films one of the encouraging candidates for microwave tunable applications.

Relaxor behavior and tunable property of lead-free Li+-doped Ba0.9Ca0.1Zr0.2Ti0.8O3 ceramics

Li+ doped lead-free Ba0.9Ca0.1Zr0.2Ti0.8O3 (abbreviated as BCZTL) ceramics were prepared through solid-state reaction method. Effects of Li+ on the formation of oxygen vacancies, change of lattice parameters and grain sizes were investigated. The disordered distribution of Li+ ions on B sites of BCZTL were found to give rise to the emergence of local random fields and facilitate the appearence of polar nanoregions (PNRs), which led to the relaxor behavior observed in dielectric measurements. The physical mechanisms for the influences of Li+ substitution and sintered temperature on the variation of PNRs, relaxor behavior and tunability were also proposed. Compared with other sintered temperatures, the 1300 °C sintered BCZTL sample exhibited relatively lower degree of relaxor behavior (γ = 1.89) and higher tunability (k = 56%) owning to the smaller PNRs size.

Electrical characteristics and conduction mechanism of microwave-sintered (Ba0.8Sr0.2)(Zr0.1Ti0.8Ce0.1)O3 electronic ceramics

This paper presents the fabrication and electrical characterization of a lead-free polycrystalline complex electronic material Ba0.8Sr0.2(Zr0.1Ti0.8Ce0.1)O3 (abbreviated as BSZTCO) using standard experimental techniques. The phase identification of the material, determined using X-ray diffraction data, depicts the formation of a multi-phase system. The various electrical parameters were obtained at different frequencies (102–106 Hz) and temperatures (20–500 °C) using the phase-sensitive meter and found interesting results. Study of the micrograph of natural surfaces of the sample suggests that the ceramic sample has been formed with high density grain growth (without any cracks or voids). The transport properties and dielectric relaxation characteristics of the material have been studied using modulus and impedance spectroscopy techniques. Temperature dependence of conduction behavior (Nyquist plot) confirms the presence of bulk and grain boundary effects in the material. The charge transfer by hopping dominates the electrical transport process of the material as revealed from conductivity analysis. The dielectric relaxation of the material is studied using a complex modulus spectrum depicting non-Debye type relaxation.

Observation of large electrocaloric properties in lead-free Ba0.98Ca0.02Ti0.98Sn0.02O3 ceramics

Tetragonal lead-free Ba0.98Ca0.02Ti0.98Sn0.02O3 (BCST) compound sintered at 1400 °C was investigated for its electrocaloric properties. The large adiabatic temperature variation, ΔT ∼ 0.476 K and isothermal entropy change, ΔS ∼ 1.90 J/kg.K were obtained at ∼ 373 K at an electric field of 20 kV/cm. Further, higher electrocaloric coefficients (ΔT/ΔE ∼ 0.238 K.mm/kV and ΔS/ΔE ∼ 0.952 J.mm/K.kg.kV) with better refrigeration capacity (RC ∼ 152 J/kg) were achieved at the same temperature and electric field. The ΔS/ΔE and RC values for this compound are better than that observed in various other lead-free ferroelectric ceramics.

Enhanced electrical properties in donor–acceptor co-doped Ba(Ti0.92Sn0.08)O3 ceramics

In this work, lead-free piezoelectric ceramics Ba0.99Li0.005Al0.005(Ti0.92Sn0.08)O3-0.5%MnO2(BLATS-M) and Ba0.99Li0.005Nb0.005(Ti0.92Sn0.08)O3-0.5%MnO2(BLNTS-M) were synthesized by a solid-state reaction process. The influence of Li+–Al3+, Li+–Nb5+ ionic pairs on the microstructure, phase structure and electrical properties of Ba(Ti0.92Sn0.08)O3-0.5%MnO2(BTS-M) was systematically investigated. An orthorhombic (O) phase structure is obtained in all ceramics at room temperature. Both Li+–Al3+ and Li+–Nb5+ ionic pairs co-doping can enhance the piezoelectricity of BTS-M ceramic, while the Li+–Nb5+ doped BLNTS-M ceramic exhibits an optimum electrical properties: the piezoelectricity coefficient (d33) = 805 pC/N, the electromechanical coupling coefficient (kp) = 0.519, the relative permititivity (er) = 31900, the converse piezoelectric coefficient $$\left( {d_{{33}}^{*}} \right)$$ = 536 pm/V and the in situ quasi-static d33 with maximum $$\left( {d_{{33}}^{{\hbox{max} }}} \right)$$ = 1620 pC/N. The dielectric properties versus DC bias electric field experiments exhibit high dielectric tunability (ƞr = 97.78%) and figure of merit (FOM = 20.96) at 100 Hz and room temperature in BLNTS-M ceramic. The results suggest an effective approach to design high-performance piezoelectrics and dielectrics by appropriately selecting the types of donor–acceptor ionic pairs.

Piezoelectric and thermophysical performances of La3+ and Ir4+ co-doped Ba0.95Ca0.05Ti0.94Zr0.06O3 ceramics

Abstract Rare earth element-doped piezoelectric ceramics exhibit excellent electrical properties. Platinum group elements can render them catalytically active and conductive. In this study, lead-free Ba0.95Ca0.05Ti0.94Zr0.06O3 piezoelectric ceramics doped with 0.12% lanthanum and iridium (varying contents, x) were sintered at 1260 °C. The thermal expansion coefficients and fracture strengths of these ceramics were affected by their strains and structural defects. With an increase in x, the diffuse phase transition weakened first and then accelerated (with further increase in x (> 0.75%)). The best ferroelectric properties were obtained at 400 ms and 25 kV/cm. The effects of the phase, structural defects, and internal stress on the electrical properties of the ceramics were systematically investigated. Relations of electrical properties, mechanical strength, and thermophysical performances were originally researched. In addition, the electrical properties (piezoelectric constants, ∼270 pC/N; mechanical quality factors, ∼70) and thermophysical performances (thermal expansion coefficient, ∼1.2 × 10−5 K−1) of the ceramics were found to be suitable for practical applications.

Phase transitions, energy storage performances and electrocaloric effect of the lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 ceramic relaxor

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the Morphotropic Phase Boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant Sodium Dodecyl Sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO3. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~80% at 120 {\deg}C. In addition, the electrocaloric responsivity was found to be 0.164.10-6 K.m/V at 360 K.

Enhancement of Tunability Properties of (Ba0.95Ca0.05)TiO3 Lead Free Ceramic by BaWO4 for Microwave Applications

Lead-free (1 − x)(Ba0.95Ca0.05)TiO3–xBaWO4 (abbreviation BCT–BW) (x = 0, 0.01, 0.015, and 0.02) composite ceramics have been synthesized by the sol gel method with subsequent thermal treatment at 1000°C/1200°C as calcined/sintering temperatures. Effect of BW on the structural characteristics and microstructure of the prepared compositions were investigated. X-ray diffraction analysis of pure BCT ceramic showed a tetragonal perovskite structure; however, the other compositions (x > 0) a two phases of BCT (tetragonal structure P4/mm space group) and BW (tetragonal I41/a space group) were detected. Microstructure observation confirmed presence both of spherical and elongated grains of BCT and BW, respectively. Effect of BW addition on the phase transition temperature can be neglected; however, it had a significant impact on decreasing the dielectric permittivity and increasing the thermal stability in all temperature ranges. The dielectric tunable properties of prepared compositions were analyzed, and the results showed an enhancement of BCT tunability properties by BW content. High dielectric tunability 70.12% (at 30 kV) was achieved in composite (0.98 BCT–0.02 BW) due to the lowest value of permittivity and dielectric loss in addition to ferroelectric to ferrorelaxor phase transition behavior for which it is considered a promising material for tunability applications.

Impact of crystal structure and microstructure on electrical properties of Ho doped lead-free BCST piezoceramics

Conventional solid state sintering method was used to synthesize lead-free (Ba0.91Ca0.09Sn0.07Ti0.93)O3-xHo2O3 (x = 0, 1.2,1.4,1.6,1.8 and 2.0 mol%) ceramics. The influence on electrical properties of the system as a result of the structural and microstructural changes introduced by the incorporation of rare earth Ho3+ ions has been investigated. The X-ray diffraction analysis reveals that Ho3+ ions completely diffuse into the (Ba0.91Ca0.09Sn0.07Ti0.93)O3 lattice to form a homogeneous solid solution with a pure perovskite structure having tetragonal symmetry. Evidence of Ho3+ substituting Ti4+ via the oxygen vacancy compensation mechanism exists in the range of 0–1.6 mol % Ho content, while the self-compensation mode is the preferred mechanism beyond 1.6 mol %. The average grain size exhibits a drastic reduction from 16 μm to 0.7 μm as the Ho content increases from 0 to 1.6 mol%, followed by a slight increase at higher Ho concentration. It suggests that addition of Ho3+ inhibits grain growth in the ceramics. In the composition range studied, increasing Ho3+ content produces a gradual decrease in the relative density from 93% to 81%, room temperature dielectric constant (εrt) from 3997 to 807, electromechanical coupling factor (kp) from 0.23 to 0.06, and piezoelectric charge constant (d33) from 102 to 38 pC/N. This degradation in the properties is attributed to the crystalline and microstructural changes driven by the increasing presence of Ho content in the ceramics.

Investigation of ferroelectric, piezoelectric and mechanically coupled properties of lead-free (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 ceramics

ABSTRACTLead-free piezoelectric ceramic (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) has been synthesised by solid-state sintering method and the effect of grain size on ferroelectric, piezoelectric, dielectric, mechanical and piezo-electro-mechanical properties was systematically studied. The compacted powders were sintered at three temperatures i.e. 1450°°C, 1500°C and 1550°C for an optimised duration of 5 h and they have exhibited well resolved morphotropic phase boundary with an average grain size ranging from 10 to 25 µm. Enhanced piezoelectric charge, d33 ∼ 560 pC/N and voltage, g33 ∼ 14.3 mV m/N coefficients were obtained for the 1450°C sintered BCZT sample. A maximum strain of around ∼0.14% was obtained which is comparable to that of lead-based piezoelectrics. Variation of relative permittivity with temperature revealed that the curves are independent of frequency, indicating the typical relaxor ferroelectric nature of the samples. A systematic study on cyclic loading was performed to evaluate piezo-electro-mechanical coefficients at different loads which showed hysteresis behaviour. High value of elastic modulus (E) and hardness (H) i.e. 262.7 ± 38.1 GPa and 13.7 ± 1.7 GPa were exhibited by samples sintered at 1450°C, which is higher than that of BCZT synthesised by wet-chemical methods. The results are discussed.

Effect of holmium doping on structural, electrical and piezoelectric properties of lead-free (Ba,Ca)(Ti,Sn)O3 ceramics

Lead-free (Ba0.91Ca0.09Sn0.07Ti0.93)O3 (BCST) ceramics, doped with holmium (Ho) in the range 0–1.0 mol%, were synthesized using conventional solid-state sintering method. XRD analyses of these ceramic samples confirm single phase pure perovskite structure. Evidence of Ho3+ substituting Ba2+ via electronic charge compensation exists in the range 0–0.4 mol%, while ionic charge compensation mechanism dominates beyond 0.4 mol%. Crystallite size and lattice strain undergo systematic change, while the room temperature dielectric constant (ert) decreases with increasing Ho content. The Curie temperature Tc and maximum dielectric constant (em) at Tc remain almost unchanged. Remnant polarization (Pr), electromechanical coupling constant (kp) and piezoelectric charge coefficient (d33) exhibit increasing trend with increasing Ho content and reach their maximum values of 8.2 µC/cm2, 25% and 220 pC/N respectively at 1.0 mol% of Ho content. The study reveals that doping of BCST system with appropriate quantity of Ho can improve its ferroelectric and piezoelectric properties.

Effects of V2O5 doping on the structure and electrical properties of BCZT lead-free piezoelectric ceramics

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-x mol%V2O5 (x = 0, 0.05, 0.15, 0.20 and 0.50) were fabricated successfully via solid-state reaction route and the effects of V2O5 doping on the phase composition, microstructure and electrical properties of the ceramics have also been studied. The results indicated that the addition of V2O5 significantly lower the sintering temperature of BCZT ceramics to 1350 °C without sacrificing the high piezoelectrical properties. XRD results revealed that the phase structure was not changed with the introduction of V2O5. The sinterablity results and the SEM graphs indicated that small amount of V2O5 could effectively increase the density and grain size of BCZT ceramics. However, the electrical properties of BCZT ceramics deteriorate rapidly when the amount of V2O5 up to 0.5 mol%. Thus, the piezoelectrical properties of BCZT-xV ceramics could be obtained at x = 0.2 mol%, which were as following: d33 = 466 pC/N, kp = 32.5%, Qm = 162, Pr = 7.735 µC/cm2, er = 3104 and tan δ = 0.03, implying promising applications for lead-free piezoelectric ceramics.

Vertically-aligned lead-free BCTZY nanofibers with enhanced electrical properties for flexible piezoelectric nanogenerators

Flexible lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-0.2 mol%Y nanofibers (BCTZY NFs) were synthesized by electrospinning and their corresponding nanogenerators (NGs) with vertical alignments were fabricated. The low-temperature sintering properties of BCTZY NFs were investigated, to optimize their synthesis path and minimize the thermal energy consumption during the sintering process. The continuity, flexibility, and stability of the BCTZ-based NFs were improved by adding Y3+. Moreover, the temperature-evolved Raman spectra displayed a high Curie temperature of 280 °C for BCTZY NFs, which was far higher than that of about 90 °C for BCTZ-based ceramic bulks, owing to the discontinuous physical property of NFs. The dielectric, ferroelectric, and piezoelectric properties of the vertically aligned BCTZY NFs/PDMS were estimated and compared with those of BCTZ NFs/PDMS composites, to verify the advantages of vertical alignments and the donor doping effect of Y3+. Vertically aligned BCTZY NF-based NGs showed an average VOC of 3.0 V and ISC of 85 nA by finger tapping, suggesting their potential applications in tiny energy harvesting.