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.     

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.     

Phenomenological modeling of phase transitions and electrocaloric effect in Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3

Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-xBCT) is a promising lead-free ferroelectric system. In this paper, we present two sets of free energy coefficients and carry out phenomenological modeling to study the phase transition and electrocaloric effect. The calculated phase diagram is in excellent quantitative agreement with experiments. Furthermore, we propose a new method based on effective internal electric field to simulate polarization in the macroscopic paraelectric state of ferroelectric relaxor. The computed composition and temperature-dependent entropy and temperature change induced by electrocaloric effect are in good agreement with the measured data available for single crystal.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Electronic structure and transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films

High-entropy perovskite thin films, as the prototypical representative of the high-entropy oxides with novel electrical and magnetic features, have recently attracted great attention. Here, we reported the electronic structure and charge transport properties of sol-gel-derived high-entropy Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃ thin films annealed at various temperatures. By means of X-ray photoelectron spectroscopy and absorption spectrum, it is found that the conduction-band-minimum shifts downward and the valence-band-maximum shifts upward with the increase of annealing temperature, leading to the narrowed band gap. Electrical resistance measurements confirmed a semiconductor-like behavior for all the thin films. Two charge transport mechanisms, i.e., the thermally-activated transport mechanism at high temperatures and the activation-less transport mechanism at low temperatures, are identified by a self-consistent analysis method. These findings provide a critical insight into the electronic band structure and charge transport behavior of Ba(Zr_0.2Sn_0.2Ti_0.2Hf_0.2Nb_0.2)O₃, validating it as a compelling high-entropy oxide material for future electronic/energy-related technologies.     

Electro-optic properties of Ba0.8Sr0.2TiO3 thin film

Electro-optic properties of Ba_0.8Sr_0.2TiO₃ (BST) film with a thickness of 1 μm deposited on the MgO (001) substrate by the rf sputtering have been studied. Structural features of the film were identified by X-ray diffraction method. It was shown, that the BST film exhibited a predominantly linear EO behavior under the applied static electric field, that have been explained according to the strong compressive stresses in the film. The polarization distribution across the gap between the electrodes when electric field is applied was also investigated experimentally and calculated. The linear EO coefficient of Ba_0.8Sr_0.2TiO₃ film with a thickness of 1 μm film was found to be r_c = 99.4 p.m./V, that is promising for various EO applications, for example, high performance EO modulator.     

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.     

Electromechanical properties of Ba(Zr0.2Ti0.8)O3 ceramics prepared by spark plasma sintering

Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared by spark plasma sintering (SPS) and conventional sintering. The dynamic field-induced displacement and small-signal remnant piezoelectric constant measured by a resonant–antiresonant frequency method were evaluated. By normal sintering, the density, grain size, and dielectric constant of the ceramics increased with sintering temperature. The BZT20 ceramics prepared by SPS were characterized by linear field-induced strain. In response to the application of post-annealing at 1300 °C, BZT20 ceramics exhibited linear strain loop and high field-induced strain corresponding to dynamic strain/field d₃₃ at 20 kV/cm of 290 pm/V. The remnant piezoelectric properties of the BZT20 ceramics were found to largely depend on the preparation conditions, including the sintering temperature and annealing temperature. The BZT20 ceramics prepared by SPS and post-annealed at 1300 °C showed Q_m and k_p values of 325 and 25.1 (%), respectively.     

Magnetoelectric,magnetodielectric effect and dielectric,magnetic properties of microwave-sintered lead-free x(Co0.9Ni0.1Fe2O4)-(1-x)[0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3)] particulate multiferroic composite

Materials with two distinct (magnetostrictive-ferroelectric) phases, i.e., x (Co_0·9Ni_0·1Fe₂O₄) -(1-x) [0.5 (Ba_0·7Ca_0·3TiO₃) −0.5 (BaZr_0·2Ti_0·8O₃)], combined at ratios of 10:90, 20:80, 30:70, and 40:60 were prepared using a hydroxide coprecipitation method. These multiferroic composites were subjected to sintering via the hybrid microwave sintering technique at 1200 °C for 20 min. Ni-substituted CFO exhibited excellent magnetic properties at room temperature, with Ms ≈ 80 emu/g, μB ≈ 3.37, Mr ≈ 19.05 emu/g, and Hc ≈ 599 Oe, as well as a high value of the magnetostriction coefficient (λ12 ≈ −118 ppm). The magnetostrictive-ferroelectric crystal phases in each composite were confirmed via X-ray diffraction analysis. The highest value of the linear magneto-electric coefficient was α = 21.6 mV/cm-Oe at a frequency of 1 kHz for the 40CNFO-60(BCT-BZT) composite, and a similar sample had the highest value of the magnetodielectric coefficient, which was approximately 3.3% at f = 1 kHz with an applied magnetic field of 1 T. The typical ferromagnetic and ferroelectric nature of each composite was confirmed by M − H and P–E hysteresis loops, respectively at room temperature. Two anomalies were observed in the temperature-dependent dielectric permittivity one at ~140 °C and another above 500 °C confirming the coexistence of two materials with distinct transition points, i.e., BCT-BZT and CNFO, respectively.     

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.     

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.     

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.     

Improved dielectric,nonlinear and magnetic properties of cobalt-doped CaCu3Ti4O12 ceramics

The dielectric properties and voltage–current nonlinearity of the pure and various cobalt-doped CaCu₃Ti₄O₁₂ (Co-doped CCTO) prepared by solid-state reactions were investigated. The improved dielectric properties in the Co-doped CCTO, with a dielectric constant $\text{ε'}$ ≈7.4?×?10⁴ and dielectric loss $\text{tan}\text{δ}$?≈?0.034, were observed in the sample with a Co doping of 5% (CCTO05) at room temperature and 1?kHz. The related multi-relaxations, RII (?20 to 40?°C) and RIII (100–150?°C), were demonstrated to be a Debye-like relaxation and a Maxwell–Wagner relaxation related to oxygen vacancies. The low dielectric loss of CCTO05 was associated with the high grain boundary resistance and the increase in cation vacancies. The improved nonlinear electrical properties (CCTO05, with nonlinear coefficients $\text{α}$?≈?5.22 and breakdown electric field ${\text{E}}_{\text{b}}$?≈?300.46?V/cm) and the ferromagnetism in Co-doped CCTO were also discussed.