Lead-free Ceramics Research Articles

The improvement of piezoelectric properties in BiFeO3–BaTiO3 lead-free ceramics prepared with heat-treated rutile TiO2

The improvement of piezoelectric properties in BiFeO3–BaTiO3 lead-free ceramics prepared with heat-treated rutile TiO2

Bandgap engineering and enhancing photovoltaic effect in NBT–BNT–xNd lead-free ceramics

Bandgap engineering and enhancing photovoltaic effect in NBT–BNT–xNd lead-free ceramics

Energy storage properties and stability in Nd3+/Ta5+ modified 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 lead-free relaxor ferroelectric ceramics under a low electric field

Due to the prevalence of wearable electronic devices, Lead-free dielectric ceramics with excellent recoverable energy storage density and efficiency at low electric fields are well worth investigating. Moreover, maintaining excellent energy storage performance (ESP) in different environments is a huge challenge for researchers. In this study, 0.6Na0·5Bi0·5TiO3-0.4Sr0·7Bi0·2TiO3 lead-free relaxor ferroelectric ceramics were modified by (Sr0.7Nd0.2) (Ta0·4Ti0.5)O3 (BNST-xSNTT x = 0, 0.02, 0.04, 0.06). On one hand, BNT has a very high polarization strength, making it a very suitable basic element for designing high energy storage dielectric materials. On the other hand, Sr0·7Bi0·2TiO3 and (Sr0.7Nd0.2) (Ta0·4Ti0.5)O3 were introduced to improve the performance of ceramics, such as inducing polar nanoregions (PNRs), refining grain size, and increasing impedance. The results demonstrate that the energy storage characteristics of BNST-xSNTT were enhanced by introducing SNTT to the BNST. The ceramics exhibited a significant grain size reduction from 0.946 μm (x = 0) to 0.346 μm (x = 0.06). In addition, a great polarization difference (ΔP = 44.29 μC/cm2) was simultaneously achieved in the x = 0.02 sample. As a result, BNST-2SNTT (x = 0.02) ceramic obtained an excellent recoverable energy density of 3.24 J/cm3 and a satisfactory efficiency of 81.4 % at a low electric field of 190 kV/cm. Furthermore, the BNST-2SNTT ceramic exhibits excellent temperature stability (20°C–140 °C), frequency stability (1 Hz–500 Hz), and cycling reliability (10°-106 cycles). The corresponding fluctuation of ESP is less than 5 %. These properties indicate that the BNST-2SNTT ceramic is an excellent dielectric material for energy storage.

Moderate Fields, Maximum Potential: Achieving High Records with Temperature-Stable Energy Storage in Lead-Free BNT-Based Ceramics

HighlightsAchieving ultrahigh energy-storage density (7.19 J cm−3) and outstanding storage efficiency (93.8%) at 460 kV cm−1 in BNT-based relaxor ferroelectric ceramics under a moderate electric field.Superior energy-storage performance accomplished through meticulous regulation of permittivity, enhancement of insulation quality, and strategic domain engineering via chemical formula optimization.The intricate structure–property relationship elucidated with precision using high-resolution transmission electron microscopy.

Unveiling the role of vanadium doping in modulating morphological and electrical properties of piezoelectric Na0.46K0.46Li0.08NbO3 ceramics for energy harvesting

We report the enhancement of ferro/piezo-electric properties of lead-free alkali based perovskite Na0.46K0.46Li0.08NbO3 (NKLN) by vanadium doping (NKLNV) for high performing piezoelectric devices. Lead-free NKLN and NKLNV ceramics are synthesized via solid state reaction route as a substitute to the lead-based ceramic for the applications in sensors, transducers, and other electronic devices. The structural phase of synthesized ceramics is found to be pure perovskite as observed from powder X-ray diffraction. In dielectric studies, Curie temperature is found to be around 450 °C for both the samples. SEM images revealed the formation of homogeneous microstructure with well-defined grains. Dense polycrystalline ceramics having grain size of about 5 μm are obtained as a result of sintering at optimised temperature of 1050 °C. The micrographs showed that the grain size begins to evolve with reduced porosity in vanadium doped NKLN. Vicker's microhardness indentation test is performed for different loads at dwell time of 30 s, in which it was observed that the V-doping has enhanced the hardness. In ferroelectric studies, NKLNV shows higher value of remnant polarization as compared to NKLN as observed in P-E hysteresis loop. Fine microstructure and larger grain size felicitated the movement and reorientation of dipoles which resulted in enhanced piezoelectric coefficient for vanadium substituted NKLN ceramics. Flexible energy harvesters were fabricated by making a composite with PDMS, and then coating a thick film over ITO/PET sheet. NKLNV-based flexible device showed an improvement in open-circuit output voltage of 13.8 V under gentle finger tapping. NKLNV ceramics are a viable lead-free alternative for dielectric, piezoelectric, and ferroelectric applications.

Enhancing energy storage efficiency in lead-free dielectric ceramics through relaxor and lattice strain engineering

Dielectric capacitors with high power density and fast charge-discharge speed play an essential role in the development of pulsed power systems. The increased demands for miniaturization and practicality of pulsed power equipment also necessitate the development of dielectric materials that possess high energy density while maintaining ultrahigh efficiency (η). In particular, ultrahigh efficiency signifies minimal energy loss, which is essential for practical applications but challenging to effectively mitigate. Here, we demonstrate a strategy of incorporating heterovalent elements into Ba(Zr0·1Ti0.9)O3, which contributes to achieving relaxor ferroelectric ceramics and reducing lattice strain, thereby improving the comprehensive energy storage performance. Finally, optimal energy storage performance is attained in 0.85Ba(Zr0·1Ti0.9)O3-0.15Bi(Zn2/3Ta1/3)O3 (BZT-0.15BiZnTa), with an ultrahigh η of 97.37% at 440 kV/cm (an advanced level in the lead-free ceramics) and an excellent recoverable energy storage density (Wrec) of 3.74 J/cm3. Notably, the BZT-0.15BiZnTa ceramics also exhibit exceptional temperature stability, maintaining fluctuations in Wrec within ∼10% and η consistently exceeding 90% across the wide temperature range of −55 °C to160 °C, and under a high electric field of 250 kV/cm. All these features demonstrate that the relaxor and lattice strain engineering strategies have been successful in achieving high-performance lead-free ceramics, paving the way for designing high-efficiency dielectric capacitors with a wide temperature range.

High piezoelectric performance in lead-free (K, Na)NbO3 ceramics under a low driving field

In this work, lead-free (K0.485Na0.485Li0.03)Nb0.8Ta0.2O3 composition was designed to control the orthorhombic-tetragonal phases boundary near the room temperature as confirmed by Rietveld analysis, high-angle annular dark field scanning transmission electron microscopy, and temperature dependent dielectric constant. A comparative study of the direct and indirect synthesis methods was carried out and their functional properties were optimized as a function of sintering temperature (Ts) and dwell time. Here, we achieved a large dynamic piezoelectric constant (d33*) of 510 pm/V under a very low electric field of 15–30 kV/cm. Moreover, an enhanced static piezoelectric constant (d33) of 335 pC/N was obtained with a high Curie temperature (TC) of 315 °C. The large d33 and d33* simultaneously with high TC in a single composition are promising results in lead-free polycrystalline ceramics. The strategic design of this work opens a new door for the possible development of novel functional materials for device applications.

High Energy Density Achieved in Novel Lead-Free BiFeO3-CaTiO3 Ferroelectric Ceramics for High-Temperature Energy Storage Applications.

The development of high-performance electrostatic energy storage dielectrics is essential for various applications such as pulsed-power technologies, electric vehicles (EVs), electronic devices, and the high-temperature aviation sector. However, the usage of lead as a crucial component in conventional high-performance dielectric materials has raised severe environmental concerns. As a result of this, there is an urgent need to explore lead-free alternatives. Ferroelectric ceramics offer high energy density but lack stability at high temperatures. Here we present a lead-free (1 - x)BiFeO3-xCaTiO3 (x = 0.6, 0.7, and 0.8; BFO-CTO) ceramic capacitor with low dielectric loss, high thermal stability, and high energy density up to ∼200 °C. The introduction of CTO (x = 0.7) to the BFO matrix triggers a transition from the normal ferroelectrics to the relaxor ferroelectrics state, resulting in a high recoverable energy density of 1.18 J cm-3 at 190 °C with an ultrafast dielectric relaxation time of 44 μs. These results offer a promising, environmentally friendly, high-capacity ceramic capacitor material for high-frequency and high-temperature applications.

Enhanced energy storage properties in BNST-based lead-free relaxor ferroelectric ceramics achieved via a high-entropy strategy

The 0.65(Bi0.5Na0.5)TiO3–0.35SrTiO3-based materials are essential for the development of pulse power capacitors. However, their low recoverable energy storage density and breakdown field strength have hindered further improvement. To address this, a high-entropy strategy based on multiscale regulation is proposed, which involves synergistically manipulating the activation energy and microstructure evolution in BNST-based ceramics through the introduction of Ba(Zr0.2Ti0.2Sn0.2Hf0.2Ta0.2)O3. The inclusion of high-insulating oxides can significantly raise the activation energy of the entire system. Furthermore, the high-entropy material can significantly increase the atomic disorder and lattice distortion, resulting in strong local polar fluctuations on several nanoscales and excellent energy storage characteristics. As a result, this approach yields an impressive Wrec of ∼ 4.89 J/cm3 and a high efficiency of ∼92.1 % at 351 kV/cm, and the outstanding thermal endurance (20∼150 °C), frequency stability (5∼1000 Hz) and fatigue (100∼105 cycles). This study provides an effective strategy for achieving excellent comprehensive performances in high-entropy ceramics.

Rare-earth element doped barium titanate-based ceramics exhibiting ultra-wide temperature span electrocaloric effect

Electrocaloric effect (ECE) refrigeration stands out as a promising alternative to conventional compression refrigeration owing to its potential for miniaturization, high energy conversion efficiency, cost-effectiveness, and environmental friendliness. However, the practical applications of ECE refrigeration in lead-free ceramics face limitations due to the challenge of achieving a substantial adiabatic temperature change (ΔT) and a wide operating temperature span (Tspan). In this study, we tackle this challenge by introducing rare-earth Sm3+ ions into Ba(Ti0·90Sn0.10)O3 (BTSn) ceramics to enhance their ECE stability. We comprehensively investigate the structural, dielectric, and ECE properties of (Ba1−3x/2Smx) (Ti0·9Sn0.1)O3 (BSmTSn, x = 0−0.03) ceramics. Our findings reveal that the incorporation of Sm3+ ions leads to a reduction in the temperature at which the permittivity reaches its maximum, accompanied by an increased dispersion compared to undoped BTSn ceramics. Particularly noteworthy is the achievement of a ΔT of 0.9 K with a Tspan of 55.5 °C in the x = 0.005 composition. Furthermore, increasing x to 0.01 enables the realization of a wide Tspan of 70 °C, starting from 30 °C. These significant enhancements in the Tspan across all BSmTSn ceramics, facilitated by the introduction of Sm3+ ions, present a promising strategy for optimizing the ECE performance of BaTiO3-based ceramics.

BaTiO3-based lead-free relaxor ferroelectric ceramics for high energy storage

Barium titanate (BaTiO3, BT) is widely used in capacitors because of its excellent dielectric properties. However, owing to its high remanent polarisation (Pr) and low dielectric breakdown field strength (Eb), achievement of high energy storage performance is challenging. Herein, a systematic strategy was proposed to reduce Pr and elevate Eb of BT via: (i) modification of the relaxor behavior by alloying it with Bi(Mg2/3Ta1/3)O3 (BMT) and (ii) heightening Eb by introducing NaTaO3 (NT) with high band gap. Consequently, the energy storage efficiency (η) of 90 % and high Eb of 780 kV cm−1 were achieved simultaneously for the BT-BMT-xNT system, which facilitated the recoverable energy density (Wrec) of 6.02 J cm−3. At 300 kV cm−1, its temperature (20–120 °C) and frequency (1–500 Hz) stabilities were found to be good. Moreover, the BT-BMT-0.15NT possessed ultrafast discharge rate (t0.9 < 51 ns) and ultrahigh power density (PD > 94 MW cm−3). This study offers an effective strategy for the design of novel high-performance dielectric energy storage materials.

Temperature stability lock of high-performance lead-free relaxor ferroelectric ceramics

Lead-free dielectric ceramics are considered a highly promising material for pulse power capacitors due to their excellent energy storage performance. However, it is challenging to achieve high-temperature energy storage performance of dielectric ceramics to meet the needs of practical applications. Here, an effective strategy for constructing temperature stability lock is designed to regulate the phase composition and temperature stability based on the polymorphic polarization structure. By realizing the ergodic-state-dominated metastable relaxation structure, high energy storage performance and temperature-insensitive structure can be achieved in relaxor ferroelectric ceramics. Taking the Bi0.5Na0.5TiO3-based solid solution as an example, we demonstrate the metastable relaxation structure induced by the proportion of phase composition. This leads to a large recoverable energy density (Wrec) of 10.7 J cm−3 and a high efficiency (η) of 91 %. Together with the good thermal stability of Wrec (7.1 ± 0.1 J cm−3) and η (86 ± 5 %) values at 500 kV cm−1 in the temperature range from 20 °C to 200 °C, outperforming all reported Bi0.5Na0.5TiO3-based energy storage ceramics. Our work provides a method for obtaining lead-free dielectric ceramics with high-temperature energy storage performance through temperature stability lock.

Strong electrocaloric response with ultrawide working temperature span in lead-free BaTiO3-based ceramics by composition design

Solid-state refrigeration technology based on electrocaloric effect provides a cost-effective and convenient approach for microelectronic device cooling. However, the working temperature range of electrocaloric materials is often narrow and incommensurate with that required by many microelectronic devices including computer chips and CPUs. In this work, the working temperature span of electrocaloric response in BaTiO3 ceramics were tuned by the simultaneous introduction of Sr and Hf (abbreviated as BSHT). Through rational variation of Sr and Hf content, not only the Curie temperature is reduced to ∼80 °C, but also the room-temperature phase structure of the ceramics can be effectively tuned from a single rhombohedral phase to coexistence of rhombohedral + orthorhombic or orthorhombic + tetragonal phases. Relaxor behavior of BSHT ceramics is evident by the frequency-dispersion of dielectric permittivity and the increased relaxor diffuseness factor γ. Temperature-dependent Raman spectra confirm that Ba0.85Sr0.15Hf0.06Ti0.94O3 (0.6BSHT) sustain a two-phase coexistence state over a broad temperature range. 0.6BSHT ceramics render a large adiabatic temperature change ΔT of 0.91 K under 40 kV cm−1 with a broad temperature span of ∼57 °C, covering the working temperature window of most microelectronic devices. Moreover, the electrocaloric response of 0.6BSHT shows excellent fatigue endurance, i.e., the adiabatic temperature change shows a trivial degradation of <4.4 % after 106 cycles. This work demonstrates that BaTiO3-based ceramics remain one of the most promising electrocaloric candidates and compositional modification is an effective route to tune the electrocaloric response for fulfilling the requirements of practical applications.

Effective regulation of breakdown strength through the synergistic effect of defect chemistry and energy band engineering in Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ceramics

A defect chemistry and energy band engineering design strategy for Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ferroelectric ceramics with an ultrahigh breakdown strength is reported.

Broadening the operating temperature span of the electrocaloric effect in lead-free ceramics via creating multi-stage phase transitions

The strategy of this study achieves a large electrocaloric response of ΔT &gt; 1 K within a temperature span of 66 °C. The cooling performance exceeds 90% and 80% of the maximum for temperature spans of 44 °C and 67 °C, respectively.

Superior energy storage performance of BiFeO3–BaTiO3–CaHfO3 lead-free ceramics

The CaHfO3-modified BiFeO3–BaTiO3 lead-free ceramic exhibiting superior recoverable energy storage density of 4.70 J cm−3 and efficiency of 79% can be considered as an excellent candidate for energy storage applications.

Simultaneous enhancement of piezoelectric properties and Curie temperature in BiFeO3–BaTiO3 lead-free ferroelectrics via simple B-site modification

The simultaneous enhancement of d33 and Tc was achieved in BF–BT by simple B-site doping.

The dielectric and energy storage performance of B-Site substitution NBT-SBT lead-free relaxor antiferroelectric ceramics

dielectric capacitors are highly desired in advanced high-power electrical systems owing to their fast charge-discharge capabilities, such as electromagnetic devices, high-power microwaves, and hybrid electric vehicles. While the performance of dielectric capacitors is mainly dominated by dielectric materials. (Na0.5Bi0.5)TiO3-(Sr0.7Bi0.2)TiO3 (NBT-SBT) as well-known dielectric ceramics attracted much attention and are widely studied owing to their combining antiferroelectric and relaxor features which achieve high energy density and efficiency. However, few studies report the compositional modification of B-site in NBT-SBT dielectric ceramics. Here, we prepared a series of MgNb2O6 doped NBT-SBT ceramics at B-Sites of the perovskite structure. Their phase structure, microstructure morphology structure, elemental distribution, dielectric and energy storage properties are systemically investigated. The resultant characterization showing minor doping MN into NBT-SBT ceramic decreases the polarization hysteresis generating an outstanding energy storage property. In addition, their energy-density variation of less than 10 % over a wide temperature range of −50 to 150 degrees. The present research offers a route for designing dielectric ceramics with enhanced energy storage performance.

Achieving excellent energy storage performance with thermal stability in lead-free AgNbO3 ceramics.

Large hysteresis and low energy density of pure AgNbO3 ceramics limit their further application in pulsed power techniques. Here, less-harmful Sm2O3-modified AgNbO3 antiferroelectric ceramics were synthesized by a rolling process, in order to improve the energy storage performance. All the Sm2O3-doped samples display reduced hysteresis due to disrupted long-range order, as certified by Raman spectra. As expected, due to the large dielectric breakdown strength and reduced hysteresis, an improved energy storage density, Wrec, of 5.85 J cm-3 and satisfactory energy efficiency, η, of 77% can be simultaneously achieved in the studied antiferroelectric ceramics, showing great superiority over other bulk electronic ceramics. Along with excellent temperature stability within the range of 20-150 °C at 320 kV cm-1 (Wrec > 4.3 J cm-3, with minimal variation of ≤4%) in the studied samples, this shows that AgNbO3-based environmentally friendly ceramics are promising materials for pulsed power techniques.

Effect of substitution on the structural, electrical properties, and dielectric relaxor behavior in lead-free BiFeO3-based ceramics.

BiFeO3-based ceramics have recently garnered much interest among researchers owing to their valuable and outstanding characteristics. For this reason, the 0.7(Na0.5Bi0.5)TiO3-0.3(Bi0.7Sm0.3FeO3) ceramic was successfully synthesized by a solid-state route. The central purpose of this research is to investigate the substitution influence of Na, Ti, and Sm on the structural, dielectric, and electric properties of 0.7(Na0.5Bi0.5)TiO3-0.3(Bi0.7Sm0.3FeO3), as well as to explore its potential applications as it exhibits multiple novel functions. Notably, a structural transition from rhombohedral R3c to orthorhombic P4mm occurred within this material. In this respect, a suitable equivalent electrical circuit was invested to assess the contributions of grains and grain boundaries to the complex impedance results. Electrical conductivity was attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the sample. The temperature dependence of the dielectric constants revealed the presence of a phase transition. The local disorder provides a dependence of the real part of the permittivity on the frequency which characterizes a relaxor ferroelectric-type behavior of a lead-free material. The modified Curie-Weiss law, in addition to the Vogel Fulcher and Debye law relationships, was utilized to analyze the diffuse transition phase. Furthermore, the studied compound displayed promising electrical properties and chemical stability and proved to be a good relaxor. In this regard, a correlation between dielectric and electric behavior near the ferro-paraelectric phase transition was established.