Novel non-stoichiometric (Ba0.91Ca0.09)x(Zr0.18Ti0.82)O3 ferroelectric ceramics with improved diffuse phase transition and dielectric tunable performance

Dielectric tunable properties in ferroelectric ceramics have been optimized by a variety of approaches, e.g., isovalent/aliovalent substitution, system composite et al., while the study of non-stoichiometric regulation on the performance of BCZT ceramics was rarely concerned. Herein, a series of novel non-stoichiometric (Ba_0·91Ca_0.09)_x (Zr_0·18Ti_0.82)O₃ (BCZTx) ceramic specimens were successfully prepared via solid-state reaction. The microstructures of BCZTx ceramics are simultaneously investigated through XRD and SEM. The diffuse phase transition (DPT) behaviour of BCZTx ceramics are studied by the Lorentz-type empirical formula. The significant enhancement of DPT behaviour is observed at x = 1.03, which probably due to the coaction of the generation of partial Schottky defects and prominent reduction of grain size. Furthermore, a high tunability (k) 87.80%, low dielectric loss (tan δ) 0.141%, and a remarkably enhanced FOM of 623 are achieved in x = 0.99 at a low DC bias electric fields (BEFs) of 7.28 kV/cm and room temperature (RT), which is superior to that of the stoichiometric BCZT ceramics and other available reported BT-based ceramics systems in term of the dielectric tunable properties. Meanwhile, it shows that the temperature dependent CQF value of x = 0.99 remained advantageous around the RT. These findings suggested that non-stoichiometric BCZTx ceramics with x = 0.99 are significantly competitive in the applications of dielectric tunable devices at RT. The non-stoichiometric regulation is an effective approach in improving the dielectric tunability properties of BCZT ceramics.     

Diffuse characteristics and piezoelectric properties of Tb-doped BCZT ceramics with CaCl2 as sintering aid

Lead-free ceramics 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + 0.2 mol% Tb and xCaCl₂ (x = 0.1,0.2 and 0.3 wt%) were prepared at different temperatures (1300, 1350 and 1410 ℃) by solid-state reaction method. The experimental results reveal that dopants can effectively promote the growth of grain at relatively low sintering temperature and CaCl₂ as the well sintering aid can produce a pronounced liquid phase to fill the gap between grains sintered at 1410 ℃ with 0.2 wt%. Relative densities and piezoelectric properties of samples can be improved by the introduction of Tb and CaCl₂. Comparing with pure BCZT, the residual polarization (P_r) and piezoelectric coefficient (d₃₃^*) of ceramics increase from 8.2 to 11.4 μC/cm² and 568–720 pm/V with 0.2 mol% Tb and 0.2 wt% CaCl₂ doped. The enhanced properties of samples may be related to the appearance of liquid phase which can increase relative densities of ceramics to 96% and the form of defect dipole in ceramics. Moreover, introduction of CaCl₂ makes dielectric peaks (T_c) move to the high-temperature zone about 13 ℃ and become more and more diffuse (γ = 1.71–1.86), which may have the potential electro-caloric effect application in ferroelectrics.     

A comparative study of direct and indirect evaluation of piezoelectric properties of electrophoreticaly deposited (Ba,Ca) (Zr,Ti)O3 lead-free piezoceramics

The development and optimisation of piezoceramics are targeted usually to enhance their piezoelectric properties evaluated by both the direct or indirect measurement methods. The presented work aims to elaborate on the correlation of one direct (Berlincourt) and two indirect (convert and field-dependent) piezoelectric measurement methods on various material states. The role of the ceramic powder treatment by ball milling and electrophoretic deposition (EPD) technique on the determined electric properties as well as basic physical and mechanical properties of (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ceramics (BCZT) was investigated. It was found that the EPD technologically supported by milling allows obtaining thick and dense deposits (>2 mm). After sintering, the BCZT ceramics with a relative density of >95%, hardness in the range of 2.3–2.9 GPa and piezoelectric coefficients of d₃₃* = 940 pm/V, d_33(E=0) = 427 pm/V and d₃₃ = 364 pC/N can be achieved. Reported results also suggest that indirect (field-dependent) and direct (Berlincourt) measurements of the piezoelectric coefficients can be comparable at optimal poling conditions.     

Ultrahigh and field-independent energy storage efficiency of (1-x)(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-xBi(Mg0.5Ti0.5)O3 ceramics

Relaxor ferroelectrics are attracting an increasing interest in the application of pulse power systems due to their excellent energy storage performance. In this paper, the (1-x)(Ba_0·85Ca_0.15)(Zr_0·1Ti_0.9)O₃-xBi(Mg_0·5Ti_0.5)O₃ ((1-x)BCZT-xBMT, x ≤ 0.2) relaxor ceramics are prepared by the solid state method. The influence of BMT on the microstructure, dielectric and energy storage properties of the prepared ceramics is investigated. The XRD results show that the peak intensity of impurities (Bi₂O₃, TiO₂ and Ba₂Bi₄Ti₅O₁₈) is gradually stronger than that of BCZT phase with x increasing. Meanwhile, the grain size of (1-x)BCZT-xBMT ceramics gradually increases on account of the appearance of impurities Bi₂O₃. Influenced by the impurities and BMT, the dielectric constant of prepared ceramics gradually decreases with x increasing. A large W_rec value of 0.65 J/cm³ with an ultrahigh η value of 97.89% is achieved at x = 0.15 due to the high breakdown strength and slim P-E hysteresis loop. Meanwhile, the η is insensitive to the electric field. The ultrahigh η leads to lesser energy loss during the charge and discharge process. It makes the 0.85BCZT-0.15BMT ceramic more attractive in the application of pulse power systems.     

Structural,ferroelectric, magnetic and magnetoelectric properties of (1-x) Ba0.85Ca0.15Zr0.1Ti0.9O3 -x La0.67Sr0.33MnO3 lead-free magnetoelectric composites

The influence of an additional La_0.67Sr_0.33MnO₃ (LSMO) magnetic phase on the structural, ferromagnetic, ferroelectric, and magnetoelectric properties of Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ferroelectric phase was studied for composites of (1-x)BCZT -xLSMO (x = 0, 25, 50, 75 and 100%). The ferroelectric BCZT sample showed a perovskite single phase formation with a tetragonal crystal structure of the P4mm space group, and the magnetic phase of LSMO presented a rhombohedral crystal structure of R3c space group as shown by XRD. The composite sample with 25% LSMO exhibited large ferroelectric and piezoelectric properties with remnant, saturation polarization, and coercive electric field P_r ~7.74 μC/cm², P_s ~11.69 μC/cm² and E_C ~12.22 kV/cm with a piezoelectric coefficient d₃₃ ~ 231 pC/N. The magnetic characterization for the composites showed that the sample containing 75% of LSMO revealed the highest remnant, saturation magnetization, and coercive field of M_r ~1.358 emu/g, M_s ~19.17 emu/g, and H_C ~33.19 Oe, respectively. Moreover, it revealed the largest magnetoelectric coupling coefficient α_ME ~2.51 mV/cm.Oe with high coupling quality at a lower applied magnetic field. The results highlight the value of these composites as lead-free room temperature magnetoelectric sensors and actuators.     

Pb-free (Ba1−xCax) (Zr0·18Ti0.82)O3 dielectric tunable ceramics with giant figure-of-merit under low electric field

Dielectric tunable devices with improved overall tunability properties are in urgent demand for tunable applications. Hence, a series of Pb-free dielectric tunable ceramics based on (Ba_1?xCa_x) (Zr_0·18Ti_0.82)O₃ (abbreviated as BCZTx, x = 0.05–0.21, corresponding to BCZT05 to BCZT21) were carefully prepared using the traditional solid-state route in this work. The crystal structure, surface morphology, dielectric properties, and tunable performance of different BCZTx ceramics at room temperature (RT) were systematically studied. The temperature-dependent dielectric tunable performance was further investigated. The phase evolutions were co-confirmed by XRD and $\frac{d{\epsilon }_r}{dT}$-T curves. Interesting, high tunability (86.09%), together with a relatively low dielectric loss (~0.19% @7.42 kV/cm) were obtained in BCZT09 ceramics at 1 kHz, resulting in a giant figure-of-merit (FOM) of 448, which implied these ceramics are promising matrix for dielectric tunable applications that operated at RT. From the Tunability?T and FOM?T curves, it can be found that Ca²⁺ incorporation can improve the temperature stability of dielectric tunable performance to a certain extent. In addition, the FOM?T curve of BCZT09 showed advantages over other compositions in the temperature range of ?20 °C–85 °C, and its maximum FOM (~886) was reached at 40 °C. These observations suggest the BCZT09 ceramic as a promising matrix for application in dielectric tunable devices operating at RT. This work may guide the design of novel high-performance tunable ceramic materials.     

Evaluation of the pore morphologies for piezoelectric energy harvesting application

Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr_0.2 Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d₃₃ piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d₃₃ with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm^-2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications.     

Structural,dielectric and ferroelectric properties of lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 ceramics prepared by Plasma Activated Sintering

Lead-free Ba_0.85Ca_0.15Zr_0.10Ti_0.90O₃ (BCZT) ceramics were prepared by Plasma Activated Sintering (PAS). The influence of PAS sintering temperature on the crystalline phase, microstructure, and, dielectric and ferroelectric properties of BCZT ceramics were studied. The phase structure of BCZT ceramics first changed from rhombohedral phase to the coexistence of rhombohedral and tetragonal phases and then to tetragonal phase as the sintering temperature increased. Microstructural characterization of BCZT ceramics indicated that PAS can obtain a compact microstructure at lower temperatures of 1150–1300 °C compared with that from common pressureless sintering. The BCZT ceramics showed different degrees of diffuseness with increased temperature, and the diffuseness exponents C are all approximately on the order of 10⁵ °C. The dielectric and ferroelectric properties of BCZT ceramics were enhanced with increased sintering temperature. BCZT ceramics sintered at 1250 °C exhibited optimum properties of room-temperature ε_r=2863, ε_m=6650, and 2P_r=25.24 μC/cm², resulting from the relatively higher tetragonal phase content of the MPB between tetragonal and rhombohedral phases together with a compact microstructure.     

Structure,electrical properties and reaction mechanism of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics synthesized by the molten salt method

Lead-free (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics with excellent electrical properties were successfully synthesized by a molten salt method (MSS). The submicron BCZT powders with pure perovskite phase were obtained by adjusting the KCl-NaCl content that was used as the eutectic salt. The effects of salt content and reaction temperature on the structure and properties of the BCZT materials were systematically investigated. Comparing with BCZT ceramics prepared by solid state method (SS), the reaction temperature of BCZT ceramics synthesized by MSS decreased approximately 200 °C. Moreover, BCZT ceramics sintered at 1360 °C with 50% eutectic salt showed the most outstanding electrical properties, which are as follows: d₃₃ = 604 pC/N, k_p = 57%, P_s = 17.11 µC/cm², P_r = 9.98 µC/cm², ε_m = 15872, ε_r = 2654 and tan δ = 0.013. In addition, this work revealed a possible reaction course processes and mechanism about MSS. The results provide a new design to optimize the performance of BCZT lead-free piezoelectric ceramics.     

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).