Enhanced energy storage property in glass-added Ba(Zr0.2Ti0.8)O3-0.15(Ba0.7Ca0.3)TiO3 ceramics and the charge relaxation

Glass additive BaO-SrO-TiO₂-Al₂O₃-SiO₂-BaF₂ is employed to enhance the microstructures and energy storage properties of the Ba(Zr_0.2Ti_0.8)O₃-0.15(Ba_0.7Ca_0.3)TiO₃ ceramics. To clarify the energy storage mechanism, the charge transportation and polarization process are investigated by thermally simulated depolarization current (TSDC). The dielectric breakdown strength increases from 4.3?kV/mm to 10.8?kV/mm for BZT-0.15BCT ceramics with 11?wt% glass additives, indicating that glasses could refine the grain size, uniform the structure, and decrease defects. Due to the micro-domain region, dielectric relaxation behavior is observed with a broadened and reduced dielectric constant peak at a large dielectric constant of about 3000?at room temperature. The largest charge energy density of 1.45?J/cm³ and discharge density of 0.17?J/cm³ are achieved for BZT-0.15BCT glass ceramics with 7?wt% glass additives. TSDC results demonstrate that dipole origin movement and charge transportation have an important effect on the dielectric properties and dielectric breakdown strength, respectively, which are largely influenced by the defects distribution state at the interfaces. Moderate domain walls could restrain the defects to inhibit the charge transportation and are harmful for the dielectric properties inversely. To achieve excellent energy storage performance, moderate domain walls are compromise of slightly degrading dielectric properties and greatly improving dielectric breakdown strength.     

Ferroelectric,dielectric, and impedance properties of Sm-modified Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics

To investigate the effect of Sm doping on the electrical properties of Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-xBCT) (x = 40, 50, 60) ceramics, three Sm-modified ceramics were prepared using the conventional solid-state reaction method. Related electrical measurements, including ferroelectric and dielectric investigations and impedance spectroscopy, were recorded for these ceramics. It was found that a tilted morphotropic phase boundary resulted from the addition of Sm, which induced the best piezoelectric properties and insulating behaviour in the Sm-BZT-60BCT sample. An abnormal P-E loop shrinkage appeared in the Sm-BZT-50BCT sample but not in the other two samples. This could be attributable to the different electronegativities between Ca²⁺ and Ba²⁺ and between Zr⁴⁺ and Ti⁴⁺, whose contents are different in varied samples and have an effect on defect-dipole alignment as well as spontaneous polarization. The activation energies for the bulk conductivity in the three composites were calculated to be 0.28 ± 0.01, 0.08 ± 0.01, and 0.36 ± 0.01 eV, confirming the existence of oxygen vacancies in our samples. The Sm dopant is responsible for the oxygen vacancies. This also leads to an increased Curie temperature in the three composites.     

Light controlled resistive switching and photovoltaic effects in ferroelectric 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 thin films

In this work, the structural and ferroelectric properties of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (0.5BZT-0.5BCT) thin films deposited at different pulse repetition rates were studied. The films deposited at pulse repetition rate of 1 Hz display the optimum values of ferroelectric polarization and dielectric permittivity and are chosen for the investigation of resistive switching and photovoltaic studies. The Pt/0.5BZT-0.5BCT/ITO capacitors show the electroforming free resistive switching (RS) and is explained based on the polarization modulation of the Schottky barrier at the 0.5BZT-0.5BCT/ITO interface. Furthermore, it is shown that the RS ratio and switching voltage can be tuned with white light illumination. The capacitors display photovoltaic effect with the open circuit voltage ≈0.8 V and the short circuit current density ≈72.6 μAcm⁻². The photovoltaic efficiency is found to be ≈0.010% and is greater than that of other perovskite ferroelectric thin films. The underlying mechanism for enhanced RS and photovoltaic effects is highlighted.     

High-pressure structural investigation on lead-free piezoelectric 0.5Ba(Ti0.8Zr0.2)O3 - 0.5(Ba0.7Ca0.3)TiO3

The solid solution 0.5Ba(Ti_0.8Zr_0.2)O₃ − 0.5(Ba_0.7Ca_0.3)T iO₃ (BCZT) has become a promising member of the lead-free piezoelectric materials because of its exceptionally high piezoelectric properties. In this study, we focus on studying pressure-dependent Raman spectroscopy, powder x-ray diffraction, and dielectric constant measurements on BCZT. The data show several structural transitions are present, where the system from ambient mixed phase (tetragonal P4mm + orthorhombic Amm2) transforms into single phase (P4mm) at 0.3 GPa, then converts into cubic phase (Pm3m) at 4.8 GPa followed by another possible structural re-ordering around 10 GPa. Although there have been a lot of unanimity with the ambient crystallographic state of BCZT, our analysis justifies the presence of an intermediate orthorhombic phase in the Morphological Phase Boundary (MPB) of BCZT phase diagram. The transformation tetragonal to cubic is indicated by the Raman mode softening, unit cell volume change, and the (Ti/Zr)O₆ octahedra distortion, which coincides with the well-known ferroelectric-paraelectric transition of the system. The sudden drop in the dielectric constant value at 4.7 GPa also confirms the loss of ferroelectric nature of the BCZT ceramic.     

Microscopic origin of the enhanced piezoelectric thermal stability in acceptor doped lead-free Ba(Ti0.8Zr0.2)O3-50(Ba0.7Ca0.3)TiO3 ceramic

Acceptor doping is effective in enhancing thermal stability in piezoceramics, while the reason underlying is still unclear and awaits explanation. In this work, through doping acceptor Mn in lead-free Ba(Ti_0.8Zr_0.2)O₃-50(Ba_0.7Ca_0.3)TiO₃ ceramic, our results show that doping Mn achieves higher depolarization temperature, even higher than Curie temperature (T_C) and simultaneously a better piezoelectric thermal stability. Through microscopic and macroscopic analysis, the enhancement can be explained by the clamping effect induced by acceptor doping, which is carefully demonstrated by symmetry-conforming short-range ordering tendency theory. Thus, this work reveals the mechanism for enhanced depolarization temperature and piezoelectric thermal stability due to acceptor doping and will help developing new thermal stable lead-free piezoceramics applicable in a wider temperature range.     

An Investigation of the Nanomechanical Properties of 0.5Ba(Ti0.8Zr0.2)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films

For practical application, the functional piezoelectric film in microelectromechanical systems should meet the requirement of physical properties, as well as the mechanical properties. In this article, 0.5Ba(Ti_0.8Zr_0.2)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (0.5BZT–0.5BCT) thin films with varied properties were prepared on (100) Si substrates via a sol–gel technique at different annealing temperatures. The effects of the annealing temperature on the morphology, piezoelectricity, hardness, and elastic modulus were studied. Particular attention was paid to the surface frictional behavior of films, and the changes in the friction force can be radically explained in terms of differences in the hardness/elastic modulus ratio and the residual stress of films. And, it reveals that the higher ratio of hardness to elastic modulus and tensile residual stress can contribute to a lower friction force for 0.5BZT–0.5BCT film during sling friction.     

Composition gradient (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 film with improved dielectric,piezoelectric and ferroelectric temperature stability

Lead-free (1-x)Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) possesses comparable piezoelectric constant with lead zirconate titanate (PZT), but its poor temperature electric performances stability and low Curie temperature limit its application. Here we designed composition graded BZT-BCT films with improved temperature stability of piezoelectric, ferroelectric, and dielectric performances over a wide temperature range, and the d₃₃ reaches 21 pm/V with hysteresis loop even at 180 °C, which is far above the Curie temperature of BZT-BCT ceramic and BZT-0.5BCT film. The excellent temperature stability is ascribed to the lattice distortion and strain gradient in the grains caused by ions diffusion, and could suppress phase transition. This work could bring forward a feasible design for dielectric/piezoelectric/ferroelectric devices operating in harsh temperature environment.     

Strong magnetoelectric effect in pulse laser deposited [Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3]/CoFe2O4 bilayer thin film

Polycrystalline bilayer thin film of multiferroic [Ba(Zr_0.2Ti_0.8)O₃‐0.5(Ba_0.7Ca_0.3)TiO₃]/CoFe₂O₄([BZT‐0.5BCT]/CFO) has been deposited on Pt/Si (100) substrate using a pulsed laser deposition technique. The dielectric analysis reveals a significant change in the dielectric constant (~39% at a typical frequency of 100 Hz) at room temperature when a magnetic field is applied, in addition to a substantial improvement in the saturation polarization. A low leakage current density (~ 5 × 10^?7 A/cm²) and a high magnetoelectric coupling coefficient (α_E) both in the transverse (~2.085 V/Oe cm) as well as in the longitudinal (~0.708 V/cm Oe) directions, indicate in‐principle usability of this system for multifunctional device applications in thin film form.     

Influence of composition on the unipolar electric fatigue of Ba(Zr0.2Ti0.8)O3‐(Ba0.7Ca0.3)TiO3 lead‐free piezoceramics

The lead‐free (1?x)Ba(Zr_0.2Ti_0.8)O₃‐x(Ba_0.7Ca_0.3)TiO₃ system is considered as promising candidate for the replacement of lead‐based piezoceramics in actuation applications, during which electric fatigue is a major concern. This issue was addressed in this work, where the unipolar fatigue resistance of three (1?x)Ba(Zr_0.2Ti_0.8)O₃‐x(Ba_0.7Ca_0.3)TiO₃ compositions with different crystallographic structures (rhombohedral, orthorhombic, and tetragonal) was evaluated. Strain asymmetry and development of an internal bias field were observed in all compositions. The decrease in the remanent polarization and the large signal piezoelectric coefficient after 10⁷ unipolar cycles was found to lie between 6%‐12% and 2%‐13%, respectively. The most pronounced fatigue was observed for the orthorhombic composition, which has the largest extrinsic contribution to strain. On the other hand, the best fatigue resistance was observed for the tetragonal composition, which has a predominantly intrinsic strain response. The correlation of fatigue resistance with strain mechanism was corroborated with determination of the Rayleigh parameters and changes in the domain morphology after cycling as confirmed by piezoresponse force microscopy.     

Strong Effect of Oxygen Partial Pressure on Electrical Properties of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films

0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT) epitaxial thin films were grown on SrRuO₃ (SRO) coated (001)‐oriented SrTiO₃ (STO) single crystal substrates by pulsed laser deposition under different oxygen partial pressures in the processing of deposition. The effects of oxygen partial pressure on structure, cation stoichiometry, surface morphology, leakage current behavior, ferroelectric, and piezoelectric properties were investigated. Both the lattice parameters and (Ba + Ca)/(Ti + Zr) cation ratio decrease with increasing oxygen partial pressure. The BCZT thin film with the ideal cation stoichiometry was obtained under 200 mTorr, giving rise to a remanent polarization P_r = 14.5 μC/cm² and effective piezoelectric coefficient d₃₃ = 96 ± 5 pm/V.     

Polarization‐Induced Photoluminescence Quenching in (Ba0.7Ca0.3TiO3)–(BaZr0.2Ti0.8O3):Pr Ceramics

Pr³⁺‐doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)TiO₃ ceramics were prepared by a solid‐state reaction method. The effects of doping concentration, sintering temperature, and ferroelectric remanent polarization on photoluminescence (PL) properties of samples were systematically investigated. The PL spectra of samples exhibit strong green and red emissions with a broad blue excitation band ranging from 430 to 500 nm, in a good agreement with all commercial blue LEDs emission wavelength. Except for the concentration and temperature PL quenching, the polarization‐induced PL quenching was obviously observed, and the degree of PL quenching changes with Pr³⁺ concentrations, the origin of the change is well interpreted by field‐induced structural phase transitions between rhombohedral (R3m) and tetragonal (P4mm) for BCZT: xPr ceramics near the morphotropic phase boundary.     

水热法合成Ba(Ti_(0.8)Zr_(0.2))O_3纳米粉体

钛酸钡(BaTiO_3)系列电子材料是一类重要的功能材料,正逐渐向小体积、功能化、大容量方向发展,常采用掺杂改性的方式提高其介电常数及稳定性。本次实验主要以TiCl_4、BaCl_2·2H_2O、ZrOCl_2、NaOH为原料,采用水热合成法制备锆钛酸钡[Ba(Ti_(0.8)Zr_(0.2))O_3,BZT]纳米粉体,并探讨反应温度、Ba/(Ti+Zr)摩尔比以及pH对BZT粉体合成的影响。实验结果表明,在反应温度为220℃,反应时间为4h,Ba/(Ti+Zr)=1.4,且pH为14时制备的BZT粉体物相单一,分散性较好,粒径较小。当提高pH及前驱物的Ba/(Ti+Zr)摩尔比及升高反应温度时,均有利于BZT晶体形成,而且粉体粒径减小。     

Microstructural,dielectric, mechanical,and biological properties of hydroxyapatite (HAp)/BZT-BCT (0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3) bio-composites with improved mechano-electrical properties for bone repair

Hydroxyapatite (HAp; Ca₁₀(PO₄)₆(OH)₂) is a commonly used biomaterial for bone tissue repair applications but it has poor electrical conductivity. Whereas, BZT-BCT (0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃) is a lead-free piezoelectric material which can mimic the stress-generated electric potential of electrically-excitable tissues such as bone. This study investigated the mechanical, electrical and bio properties of xHAp/(1-x)BZT-BCT composites. xHAp/(1-x)BZT-BCT composites (with x = 5, 10, 15 and 20 wt%) were synthesized by high energy ball milling (HEBM) assisted solid-state reaction route. X-ray diffraction, scanning electron microscopy, density measurements and cell-material interaction studies of sintered HAp/BZT-BCT composites were carried out and discussed in detail. Dielectric properties of sintered composites were evaluated and compared with the existing theoretical models. Different mechanical properties like Vicker's hardness, fracture toughness, and diametral tensile strength were measured to assess the usability of synthesized composites for load-bearing orthopaedic applications. These various studies showed that incorporation of BZT-BCT in HAp improved its mechanical and electrical properties and thereby significantly increased the proliferation of human osteogenic MG-63 cells. Among all the composites, better mechanical, electrical and biological properties were obtained in 10HAp/90BZT-BCT composites.     

Phase characteristics,microstructure, and electrical properties of (1-x)BaZr0.2Ti0.8O3-(x)(Ba0.7Ca0.3)0.985La0.01TiO3 ceramics

In this study, (1-x)BaZr_0.2Ti_0.8O₃-(x)(Ba_0.7Ca_0.3)_0.985La_0.01TiO₃ ((1-x)BZT-(x)BCLT) ceramics, where x = 0.3, 0.4, 0.5, and 0.6, were prepared employing a conventional solid-state sintering technique. X-ray diffraction patterns and dielectric measurements indicated three phase regions at room temperature, including a single rhombohedral (x = 0.3), a phase coexistence of rhombohedral and tetragonal (x = 0.4), and a single tetragonal structure (x ≥ 0.5). X-ray photoemission spectra at the surface of ceramics confirmed the oxidation state of Ba²⁺, Ca²⁺, Ti⁴⁺, and Zr⁴⁺ ions. Upon BCLT addition, the reduction of the average grain size and the presence of the tetragonal structure significantly affected the dielectric, ferroelectric, and piezoelectric properties of these ceramics. With these results, the composition x = 0.3 showed maximum ε_r′ and ε_m′, whereas the composition x = 0.5 showed maximum P_r, E_c, d₃₃, k_p, and d¹₃₃ factors. These results suggest a new phase diagram for the (1-x)BZT-(x)BCLT system, which could be tuneable by BCLT concentration and might be useful as an alternative material in dielectric, ferroelectric, and piezoelectric devices.     

Pyroelectric energy harvesting using low–TC (1–x)(Ba0.7Ca0.3)TiO3–xBa(Zr0.2Ti0.8)O3 bulk ceramics

Lead‐free ferroelectric ceramics (1–x)(Ba_0.7Ca_0.3)TiO₃–xBa(Zr_0.2Ti_0.8)O₃ (BCTZ100x) with x = 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, and 0.80 were evaluated for their pyroelectric energy harvesting performance, using the Olsen cycle. As the composition ratio x increased, the crystal phase changed to tetragonal, orthorhombic, rhombohedral, and cubic; the phase boundaries crossed each other in the vicinity of BCTZ70. The crossover phase transition behavior between first‐order and diffuse phase transition changed to only the diffusion phase transition with increasing x. A pinching effect occurred because an increase in dielectric constant was also observed. Energy densities N_D of 229 mJ/cm³ and 256 mJ/cm³ for BCTZ50 and BCTZ80 were obtained, respectively, in temperature of 30°C‐100°C and an electric field of 0‐30 kV/cm. These N_D values are over two times higher than that of soft–Pb(Ti,Zr)O₃ (PZT), which exhibits piezoelectric performance equivalent to BCTZ50 at room temperature. Compared with soft–PZT, BCTZ50 and BCTZ80 exhibited larger N_D values owing to their lower Curie temperatures (T_C ~ 50°C‐110°C). We conclude that low–T_C ferroelectrics are useful for pyroelectric energy conversion based on the Olsen cycle even if they are unsuitable for piezoelectric applications at high temperatures.     

Influence of the Strain on Dielectric and Ferroelectric Properties of 0.5BaZr0.2Ti0.8O3–0.5Ba0.7Ca0.3TiO3

0.5BaZr_0.2Ti_0.8O₃‐0.5Ba_0.7Ca_0.3TiO₃ ceramic and its epitaxial films on (0 0 1) SrTiO₃ substrate were prepared to compare their dielectric and ferroelectric properties. The ceramic has a high dielectric permittivity, a weak dielectric relaxation, a low ferroelectric Curie temperature (T_C) of 60°C and a fast polarization relaxation. The films show much lower dielectric permittivities and mild dielectric relaxations. Furthermore, the T_C of film with 40, 100, and 200 nm thickness is 155°C, 110°C, and 60°C, respectively, because the epitaxial strain decreases with the film thickness increasing. The higher the T_C is, the more stable the room‐temperature polarization is.     

Ba(Zr0.3Ti0.7)O3薄膜的结构及性能

用溶胶-凝胶法分别在Pt/Ti/SiO2/Si和LaNiO3/Pt/Ti/SiO2/Si衬底上制备了锆钛酸钡[Ba(Zr0.3Ti0.7)O3,BZT]薄膜.相结构及介电性能研究表明:衬底和薄膜厚度对BZT薄膜性能具有显著影响.制备在LaNiO3/Pt/Ti/SiO2/Si衬底上的BZT薄膜具有(100)面的择优取向,其介电常数及介电损耗则随着薄膜厚度的增加而降低.对制备在Pt/Ti/SiO2/Si衬底上的BZT薄膜,在薄膜厚度低于500nm时,其介电常数随薄膜厚度增加而增加,大于500nm时又有所减小.     

The Effect of Electric Poling on the Performance of Lead‐Free (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 Piezoceramics

The effect of increasing poling fields on the properties of (1?x)BZT–xBCT compositions across the morphotropic phase boundary (MPB) is studied using large signal polarization and strain, small signal permittivity and piezoelectric coefficient, and XRD measurements. Successive poling causes charge carrier migration inducing an internal bias field, which becomes large with respect to the coercive field resulting in biased ferroelectric and ferroelastic switching. Improvements in piezoelectric coefficient of 9% are significantly smaller in the tetragonal 60BCT composition compared with the improvement of approximately 50% in the rhombohedral 40BCT and MPB 50BCT compositions. While the properties continue to change with increased poling fields, the remnant ferroelastic domain texture parallel to the field direction, as observed from XRD, stays approximately constant. The improvement in overall domain alignment leading to largely enhanced intrinsic piezoelectricity originates from the alignment of 180° domains and possibly non‐180° domains in grains with orientations inclined to the electric field. As a result, poling is most effective in BZT–BCT materials that have low coercive fields, show low distortions and possess more polarization orientations, such as compositions in the rhombohedral phase field or near the MPB.     

Processing of 0.55(Ba0.9Ca0.1)TiO3-0.45Ba(Sn0.2Ti0.8)O3 lead-free ceramics with high piezoelectricity

We report a large piezoelectric constant (d₃₃), 720 pC/N and converse piezoelectric constant (d₃₃^*), 2215 pm/V for 0.55(Ba_0.9Ca_0.1)TiO₃-0.45Ba(Sn_0.2Ti_0.8)O₃ ceramics; the biggest value achieved for lead-free piezoceramics so far. The ceramic powders were calcined between 1050°C-1350°C and sintered at 1480°C. The best properties were obtained at a calcination temperature (CT) of 1350°C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 µm, ceramics density ~95%, and grain size ~40 µm led to a formation of orthorhombic-tetragonal-pseudo-cubic (O-T-PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (ε_r) >5000 and a low loss tangent (tan δ) of 0.029. In addition, the d₃₃ value stabilizes in the range of 400-500 pC/N for all samples calcined between 1050°C and 1250°C. The results entail that the (Ba,Ca)(Sn,Ti)O₃ ceramics are strong contenders to be a substitute for lead-based materials for room temperature applications.