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Relaxor ferroelectrics are primary candidates for high-performance energy storage dielectric capacitors. For the practical application of capacitors, high energy storage density and high efficiency (η) are both required, the pursuit of which remains challenging. Herein, a novel 0.88Bi0.47Na0.47Ba0.06TiO3-0.12Sr(Ni1/3Nb2/3)O3 (12SNN) lead-free ceramic is proposed to enhance the energy storage properties by modulating highly dynamic polymorphic polar nanoregions (PNRs). The introduction of SNN leads to the formation of PNRs with high flexibility, regulates the ratio of rhombohedral and tetragonal PNRs, avoids polarization saturation at an electric field far below the breakdown field, and suppresses the energy loss. As a result, a high recoverable energy density (Wrec) of 7.0 J cm−3 and a high η of 81.5% are achieved simultaneously. Additionally, the superior performance is maintained across a wide range of temperatures (25–120 °C) and frequencies (1–500 Hz). Our findings indicate that the novel 12SNN ceramic shows excellent overall energy storage performance and provides a feasible method for exploring high-temperature applications in capacitors. [ABSTRACT FROM AUTHOR]

The realization of thermally stable Tb3+-doped green emission at high temperatures in solid-state lighting is still a crucial challenge. Nevertheless, the study on modulating the thermally stable luminescence at high temperatures is seldom reported. The position of the intervalence charge transfer (IVCT) energy level is used to systematically investigate the thermal quenching performance of Tb3+-activated green-emitting phosphors with varying concentration gradients of Gd1−xTaO4:xTb3+ (x = 0.1%, 0.5%, and 2%) in this study. The IVCT energy levels were determined according to the empirical formula to show a decreasing trend, consistent with the position of the IVCT energy levels measured in the excitation and diffuse reflectance spectra. Moreover, the thermal quenching performance of different wavelength excitation positions (host absorption, 4f–5d of Tb3+, and Tb3+–Ta5+ IVCT band) is quite different. The modulation of thermal quenching performance among distinct phosphors when subjected to host excitation or IVCT excitation can be elucidated through optimal positions within the energy levels associated with IVCT. The diverse concentration gradient samples exhibit varying degrees of thermal quenching performance in the variable-temperature spectra. The fluorescence lifetimes of the samples are generally comparable but slightly lower. The quantum efficiency rapidly improves as the Tb concentration increases. The underlying mechanism governing this phenomenon is elucidated by constructing a model that encapsulates the interplay between the compensating and quenching channels, in addition to the energy conversion of Tb3+ into Gd3+. The abovementioned results indicate that the dual driving scheme of the doping concentration and excitation wavelength is an effective means to regulate the thermal quenching performance of Tb-activated green-emitting tantalate phosphors. [ABSTRACT FROM AUTHOR]

The utilization of phosphor materials has always been a significant challenge in terms of improving thermal quenching performance. In this work, the thermal quenching performance tuning mechanism which establishes the band gap and thermal quenching correlation patterns is proposed. The crystal field splitting energy Dq was decreased by changing the surrounding crystal lattice environment of Bi3+ through a solid solution replacement, and the thermal quenching activation energy ΔE of Bi3+ was tuned from 0.117 eV to 0.182 eV accordingly. At 423 K, the luminous intensity increases from 0.101 to 0.396 of the preliminary intensity at 303 K with increasing substitution. In addition, the band gap value of Bi3+ calculated by diffuse reflectance spectroscopy increased from 4.40 eV to 4.72 eV, which corresponds to a linear positive correlation between the band gap and the thermal quenching properties. Furthermore, a monophase white-emitting phosphor with good thermal stability was prepared by constructing a Bi3+–Eu3+ co-doping system. In particular, the relative sensitivity of Sr for temperature measurement applications reached 3.17% K−1 based on the double-luminescence fluorescence intensity ratio. Thus, this modulation scheme can be used as a reference for the design of various phosphor materials with tunable thermal quenching properties in the future. [ABSTRACT FROM AUTHOR]

Reducing or even prohibiting the use of toxic lead in electronic devices has become one of the most cutting-edge topics in various disciplines. The recently proposed phase boundary engineering endows lead-free piezoceramics with comparable performances to that of some lead-based piezoceramics. However, the enhancement in performance hinges on the coexistence of multi-phases and complex domain structures, particularly the occurrence of nano-domains and polar nanoregions (PNRs). Although nano-domains have been significantly studied in lead-based piezoceramics, understanding the nano-domains and PNRs in lead-free piezoceramics is in its infancy and needs a systematic summary and in-depth analysis. Herein, we summarize the nano-domains and PNRs in three representative lead-free piezoceramics (i.e., potassium sodium niobate, barium titanate, and sodium bismuth titanate), focusing on their effects on macro performance. First, we introduce the foundation and tools for the observation of the domains. Then, we summarize the variations in the nano-domains with phase structure, electric field, and temperature, and their effects on performance including piezoelectricity, strain, temperature stability, aging, and fatigue. Finally, we present our perspectives on the future of nano-domains, concentrating on nano-domain engineering. Therefore, this review can help better understand the nano-domains and PNRs in lead-free piezoceramics, and be used for the further development of high-performance lead-free piezoceramics. [ABSTRACT FROM AUTHOR]

Developing eco-friendly high-performance piezoceramics without lead has become one of the most advanced frontiers in interdisciplinary research. Although potassium sodium-niobate {(K,Na)NbO3, KNN} based ceramics are believed to be one of the most promising lead-free candidates, the relatively inferior piezoelectric properties and strong temperature dependency have hindered their development for more than 50 years since being discovered in the 1950s. It was not until 2014 that our group initially proposed a new phase boundary (NPB) that simultaneously improved the piezoelectric properties and temperature stability of non-textured KNN-based ceramics to the level of partly lead-based ceramics. The NPB has been then proved by some researchers and believed to pave the way for "lead-free at last" proposed by E. Cross (Nature, 2004, 432, 24). However, the understanding of the NPB is still in its infancy, leaving many controversies, including the phase structure and physical mechanisms at the NPB as well as the essential difference when compared with other phase boundaries. In this context, we systematically summarized the origin and development of the NPB, focusing on the construction, structure and intrinsic trait of the NPB, the effects of the NPB on the performance, and the validity and related incipient devices of the NPB. Particularly, we concluded the phase structure and domain structure locating at the NPB, analyzed the physical mechanisms in depth, proposed the possible methods to further improve the performance at the NPB, and demonstrated the validity and scope of the NPB as well as the device application. Finally, we gave out our perspective on the challenges and future research of KNN-based ceramics with NPB. Therefore, we believe that this review could promote the understanding of the NPB and guide the future work of KNN-based ceramics. [ABSTRACT FROM AUTHOR]

Electrostrictors offer unique advantages over piezoelectrics, including no poling process, temperature stability and hysteresis-free strain characteristics. Learning from the distinction between disordered and ordered ABI0.5BII0.5O3 perovskite-structured electrostrictors, the electrostrictive effect enhances with a smaller active space for B ions. Here, we propose a novel design strategy to arouse the potential capacity of electrostriction in BaTiO3-based materials by A-site Li+–Ho3+ ion-pairs engineering. In this way, limited active space for a Ti-site is expected due to the contracted oxygen octahedron around ion-pairs, resulting in smaller polarization per unit magnitude of electric field but a larger strain per unit magnitude of polarization and therefore an enhanced longitudinal electrostrictive coefficient Q33. A systematic analysis evidenced that Li+ and Ho3+ ions tend to occupy the neighboring Ba-sites in one unit cell of BaTiO3, and directly form Li+–Ho3+ ion-pairs along the [001] direction. Besides, partial fragmented domain patterns induced by local structural heterogeneity due to the involvement of ion-pairs are detected in samples with higher dopants, benefiting suppression of hysteresis in strain curves. Consequently, the (Li, Ho) co-doped BaTiO3 ceramics by A-site engineering exhibit giant Q33 up to 0.06 m4 C−2 which is superior to other lead-bearing/free electrostrictive materials, meeting the requirement of a thermal stability (20–150 °C) – low hysteresis (＜10%) – large strain (0.12–0.2%) combination stimulated by the outstanding electrostrictive effect. Our research provides a new paradigm for designing applicable high-performance electrostrictive materials through A-site engineering. This is expected to benefit a wide range of functional materials. [ABSTRACT FROM AUTHOR]

The understanding of high piezoelectricity in potassium sodium niobate (KNN)-based ceramics with a new phase boundary has been limited to unpoled samples. Here, the phase structure, domain structure, and phenomenological theory were studied on both unpoled and poled samples by taking (0.99 −x)(K0.48Na0.52)(Nb0.955Sb0.045)O3–0.01SrZrO3–x(Bi0.5Ag0.5)ZrO3 ceramics as an example. Shifting the phase transition temperatures to room temperature can result in the coexistence of a ferroelectric matrix containing an orthorhombic–tetragonal (O–T) coexisting phase and rhombohedral (R)-related polar nanoregions (PNRs), and then the miniature and nanoscale domain structure can be demonstrated. During the poling process, the R phase-related PNRs can facilitate domain switching and polarization rotation, resulting in a single domain structure and enhanced evidence of the R phase. Therefore, high piezoelectricity originates from a single domain feature as well as the diffused multi-phase coexistence in association with R phase related PNRs. This study provides a systematic approach to understand the physical mechanisms of enhanced piezoelectricity in KNN-based ceramics. [ABSTRACT FROM AUTHOR]

For eco-friendly bismuth sodium titanate (Bi0.5Na0.5TiO3)-based materials, ultrahigh poling strain (Spol) is always accompanied with a sizable remnant strain (Srem), which severely restricts the cycling reliability of their superior electro-strain. Composition engineering is an effective way of eliminating Srem, but Spol will be sacrificed as well, leading to an overall inferior electro-strain. Here, by composition engineering and subtle criticality confinement, a giant recoverable electro-strain (S ＞ 0.7%, realizing Srem modulation without Spol sacrifice) with reduced hysteresis is reported in BNT-based relaxor ferroelectrics, which can be kept at a high level (＜2% variation) even after 105 fatigue cycles. As disclosed by the detailed electric field-dependent multi-scale analyses, the electro-strain behavior is tightly associated with the agglomeration and deagglomeration process of polar clusters. More efficient release of mechanical mismatch stress among interacting polar entities is suggested to facilitate the deagglomeration process of polar clusters, ensuring a faster restoration of the electric field-induced ferroelectric state when the electric field is removed, which is responsible for the reduced hysteresis and the excellent fatigue performance. These results indicate the significance of “subtle criticality confinement”, and the insight for the design of polycrystalline ceramics with giant and anti-fatigue electro-strain may be useful to develop a new generation of eco-friendly actuators. [ABSTRACT FROM AUTHOR]

In this work, (0.99 −x)(K0.5Na0.5)(Nb0.965Sb0.035)O3–0.01SrZrO3–x(Bi0.5Na0.5)ZrO3 ceramics were selected to show how a phase engineering strategy (PES) affects the strain properties in potassium sodium niobate (KNN)-based ceramics. The application of PES resulted in the coexistence of multiple phases in KNN-based ceramics accompanied by an increased diffuseness of ferroelectricity and decreased domain size. The strain properties, including the dependencies of strain on composition, temperature and fatigue behavior, were evaluated by considering the phase structure, domain configuration and microstructure. The improved room-temperature strain properties of the KNN-based ceramics with PES originated from the converse piezoelectric response, domain switching and possible electric-induced phase transition, which resulted from the coexistence of multiple phases and complex domain configuration. The enhanced temperature stability mainly originated from the converse piezoelectric response. Endurable fatigue resistance (no degradation within 100–105 electric cycles) and a high electrostriction coefficient (Q33 = 0.035 m4 C−2) were observed in the ceramics with x = 0.03 and 0.05, respectively. This study provides a systematic analysis of the effects of PES on strain properties in KNN-based ceramics. [ABSTRACT FROM AUTHOR]

AgI/Bi5O7I plate composite was fabricated at room temperature by the phase transition and morphological transformation of BiOI microspheres. The orange BiOI microsphere was transferred to light yellow AgI/Bi5O7I plate by the addition of NaOH and AgNO3 to the system. The formation process and possible transformation mechanism of AgI/Bi5O7I plate were detected and are discussed. The visible light absorption area of AgI/Bi5O7I extended to 667 nm and photo-excited electrons migrated from Bi5O7I to AgI to effectively inhibit the recombination of photo-generated carriers in the Z-scheme AgI/Bi5O7I plate. As a result, the photocatalytic ability of AgI/Bi5O7I plate increased by a factor of 21.9 than that of pure Bi5O7I and a factor of 45.7 than that of pure AgI under visible light irradiation. This study provides a facile fabrication of Z-scheme visible light photocatalysts with high performance and a method for designing semiconductor photocatalysts with controllable morphology. [ABSTRACT FROM AUTHOR]

In this study, 0.96KNNSx–0.01SZ–0.03BNZ ceramics (x = 0–0.08) were used as examples to illustrate the effects of phase boundaries on strain property and temperature stability. The addition of Sb5+ resulted in a rhombohedral–tetragonal (R–T) phase boundary at x = 0.05–0.07, as confirmed by temperature-dependent Raman spectra. In the R–T region, an improved piezoelectric constant (d33 = 390–440 pC N−1) and high unipolar strain (Suni = 0.14–0.15%) were observed due to the dominating intrinsic contribution. More importantly, a favorable temperature stability of Suni was observed in the ceramics with x = 0.05; for example, there was a slight variation of +5% to −13% when the temperature was increased from 20 °C to 180 °C. Through systematic investigations of composition and temperature-dependent strain, methods to improve Suni and consolidate its temperature stability in KNN-based ceramics were subsequently suggested. We believe that this study can promote the understanding and design of KNN-based ceramics with high strain and favorable temperature stability. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectrics are receiving an increasing amount of attention because of their superior energy-storage density. Due to environmental concerns, lead-free alternatives are highly desirable, with bismuth sodium titanate highlighted for its energy-storage applications. Here, we realized an enhancement in energy-storage performance with a recoverable energy density (Wrec) of 2.42 J cm−3 (low electric field of E = 143 kV cm−1) in {Bi0.5[(Na0.8K0.2)0.90Li0.10]0.5}0.96Sr0.04(Ti0.975Ta0.025)O3 ceramics by a hot-pressed sintering (HPS) method, which is greatly superior to the reported perovskite ceramics under similar electric fields. In addition, excellent fatigue and thermal stabilities (variation of Wrec≤ 0.047% after 105 cycles and Wrec ＞ 2 J cm−3 over 25–175 °C) can be observed. The HPS method greatly increases the dielectric breakdown strength (DBS ∼ 143 kV cm−1) because of a denser structure consisting of large and small grains, which is superior to those (78–97 kV cm−1) of spark plasma sintering (SPS), conventional air sintering (CAS), and MnO aids sintering (AS) methods. In addition to the contribution of the enhanced breakdown strength, the ultrahigh energy-storage density is also due to the almost complete RE to FE transition resulting from strain, polarization, and current density versus electric field (S–E, P–E, j–E) loops. Interestingly, a giant strain of 0.65% can also be found by the HPS method. In particular, a conceptual model based on the nature of relaxor ferroelectrics is employed to understand the excellent energy-storage properties observed in this work. We believe that the findings in this work may provide future tips and guidance for this direction of study. [ABSTRACT FROM AUTHOR]

The realization of thermally stable Tb 3+ -doped green emission at high temperatures in solid-state lighting is still a crucial challenge. Nevertheless, the study on modulating the thermally stable luminescence at high temperatures is seldom reported. The position of the intervalence charge transfer (IVCT) energy level is used to systematically investigate the thermal quenching performance of Tb 3+ -activated green-emitting phosphors with varying concentration gradients of Gd 1- x TaO 4 : x Tb 3+ ( x = 0.1%, 0.5%, and 2%) in this study. The IVCT energy levels were determined according to the empirical formula to show a decreasing trend, consistent with the position of the IVCT energy levels measured in the excitation and diffuse reflectance spectra. Moreover, the thermal quenching performance of different wavelength excitation positions (host absorption, 4f-5d of Tb 3+ , and Tb 3+ -Ta 5+ IVCT band) is quite different. The modulation of thermal quenching performance among distinct phosphors when subjected to host excitation or IVCT excitation can be elucidated through optimal positions within the energy levels associated with IVCT. The diverse concentration gradient samples exhibit varying degrees of thermal quenching performance in the variable-temperature spectra. The fluorescence lifetimes of the samples are generally comparable but slightly lower. The quantum efficiency rapidly improves as the Tb concentration increases. The underlying mechanism governing this phenomenon is elucidated by constructing a model that encapsulates the interplay between the compensating and quenching channels, in addition to the energy conversion of Tb 3+ into Gd 3+ . The abovementioned results indicate that the dual driving scheme of the doping concentration and excitation wavelength is an effective means to regulate the thermal quenching performance of Tb-activated green-emitting tantalate phosphors.

In our work, a totally anomalous thermal quenching phenomenon of red-shifted and enhanced charge transfer state (CTS) absorption is found for the first time in LiTaO 3 : x Pr 3+ phosphors. The crystal structure, luminescent properties and the mechanism of abnormal thermal quenching were investigated in detail.

The utilization of phosphor materials has always been a significant challenge in terms of improving thermal quenching performance. In this work, the thermal quenching performance tuning mechanism which establishes the band gap and thermal quenching correlation patterns is proposed. The crystal field splitting energy D q was decreased by changing the surrounding crystal lattice environment of Bi 3+ through a solid solution replacement, and the thermal quenching activation energy Δ E of Bi 3+ was tuned from 0.117 eV to 0.182 eV accordingly. At 423 K, the luminous intensity increases from 0.101 to 0.396 of the preliminary intensity at 303 K with increasing substitution. In addition, the band gap value of Bi 3+ calculated by diffuse reflectance spectroscopy increased from 4.40 eV to 4.72 eV, which corresponds to a linear positive correlation between the band gap and the thermal quenching properties. Furthermore, a monophase white-emitting phosphor with good thermal stability was prepared by constructing a Bi 3+ -Eu 3+ co-doping system. In particular, the relative sensitivity of S r for temperature measurement applications reached 3.17% K -1 based on the double-luminescence fluorescence intensity ratio. Thus, this modulation scheme can be used as a reference for the design of various phosphor materials with tunable thermal quenching properties in the future.

Sodium (Na) metal is a very encouraging anode material for next-generation rechargeable batteries owing to its high specific capacity, earth-abundance and low-cost. However, the application of Na metal anodes (SMAs) is hampered by dendrite growth and "dead" Na formation caused by the uncontrollable Na deposition, leading to poor cycle life and even safety concerns. Herein, a high-performance Na anode is designed by introducing an artificial VN interlayer on the Na metal surface (Na/VN) by a simple mechanical rolling process to regulate Na nucleation/deposition behaviors. The density functional theory (DFT) and experiment results uncover that the VN possesses high "sodiophilicity", which can facilitate the initially homogeneous Na nucleation and cause Na to distribute evenly on the VN interlayer. Therefore, uniform Na deposition with dendrite-free morphology and prolonged cycling lifespan (over 1060 h at 0.5 mA cm -2 /1 mA h cm -2 ) can be realized. Moreover, the full cell assembled by coupling a Na 3 V 2 (PO 4 ) 3 (NVP) cathode and Na/VN anode presents superior cycling performance ( e.g. , 96% capacity retention even after 800 cycles at 5C). This work provides a promising direction for regulating Na nucleation and deposition to achieve dendrite-free metal anodes.

AgI/Bi5O7I plate composite was fabricated at room temperature by the phase transition and morphological transformation of BiOI microspheres. The orange BiOI microsphere was transferred to light yellow AgI/Bi5O7I plate by the addition of NaOH and AgNO3 to the system. The formation process and possible transformation mechanism of AgI/Bi5O7I plate were detected and are discussed. The visible light absorption area of AgI/Bi5O7I extended to 667 nm and photo-excited electrons migrated from Bi5O7I to AgI to effectively inhibit the recombination of photo-generated carriers in the Z-scheme AgI/Bi5O7I plate. As a result, the photocatalytic ability of AgI/Bi5O7I plate increased by a factor of 21.9 than that of pure Bi5O7I and a factor of 45.7 than that of pure AgI under visible light irradiation. This study provides a facile fabrication of Z-scheme visible light photocatalysts with high performance and a method for designing semiconductor photocatalysts with controllable morphology.

In this work, (1 - x)(K0.48Na0.52)(Nb(0.95-y-z)Ta(z)Sb(y))O3-xBi0.5(Na0.82K0.18)0.5ZrO3, {abbreviation: KNNST-BNKZ-x-y-z} lead-free piezoceramics were prepared by a conventional solid-state reaction method, and the composition dependence of their phase structures and electrical properties was systematically discussed. Doping with Sb(5+), Ta(5+), and BNKZ plays an important role on the phase boundaries as well as piezoelectric activity. A three-phase coexistence involving rhombohedral-orthorhombic-tetragonal (R-O-T) phases was observed in the ceramics with 0.0325 ≤ x ≤ 0.05, 0.035 ≤ x ≤ 0.065, 0.05 ≤ z ≤ 0.08, indicating that doping with BNKZ, Ta(5+), and Sb(5+) can induce the formation of such a phase boundary by simultaneously increasing TR-O and decreasing TO-T. Enhanced piezoelectric behavior was observed in the ceramics located in the composition region of the R-O-T phase boundary, and a high d33 value of 400 pC N(-1) can be attained by refining their compositions (e.g., x = 0.0325, y = 0.035, and z = 0.05), together with a high TC value of ∼240 °C. Of particular interest is that a large electric field-induced strain of 0.18% (Smax/Emax = 706 pm V(-1)) was also found in the ceramics with x = 0.0325, y = 0.035, and z = 0.05 under a low electric field of 2.5 kV mm(-1). As a result, the piezoelectric activity as well as the strain can be operated in the material system by refining x, y, and z content.