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•Rare earth ions were used to optimize the strain properties of BNT-based ceramics with ergodic relaxor state.•Rare earth doping can facilitate the transition between relaxor and ...ferroelectric states.•Rare earth doping can improve the short-range polar correlation and elevate the electrostrictive effect.•Large strain value (∼0.23-0.33%) with low hysteresis of ∼8-30% was obtained from room temperature to 100 oC.
Electric field-induced high strain with small hysteresis and good temperature stability is necessary for piezoactuators devices. Most of previous works focus on the giant strain achieved in Bi0.5Na0.5TiO3 (BNT)-based ceramics through electric field-induced transition from nonergodic relaxor to ferroelectric state, while the high remnant strain or/and large hysteresis are always accompanying. In this work, through enhancing the local polarization by rare earth ions doping (e.g., La3+), we propose to improve the strain properties of BNT-based lead-free ceramics with ergodic relaxor state which displays the near zero remnant strain, small hysteresis, high temperature stability but the low strain value. The addition of La3+ would not change the ergodic relaxor state, but can improve the short-range correlation of local polar nanoregions, cut down the critical electric field of transition between relaxor and ferroelectric states, and elevate the electrostrictive effect of ceramics. Finally, high strain of ∼0.3 % with low hysteresis of ∼8−30 % was obtained in the broad temperature range from room temperature to 100 °C, which is superior to previous BNT-based ceramics and other lead-based/lead-free ceramics. This work affords a paradigm to regulate the ergodic relaxor state to optimize the strain properties, which give the significant guide for strain developments.
The intensive demands of microelectronics and energy-storage applications are driving the increasing investigations on the colossal permittivity (CP) materials. In this study, we designed a new ...system of Dy and Nb co-doped TiO2 ceramics (Dy0.5Nb0.5) x Ti1–x O2 with the formation of secondary phases, and then the enhancement of overall dielectric properties (εr ∼ 5.0–6.5 × 104 and tan δ < 8%) was realized in the broad composition range of 0.5 ≤ x ≤ 5%. More importantly, effects of secondary phases on microstructure, dielectric properties, and stability were explored from the views of defect-dipoles and internal barrier layer capacitance (IBLC) effect. According to the defect-dipoles theory, the CP should mainly originate from Nb5+, and the Dy3+ largely contributes to the decreased dielectric loss. Both CP and low dielectric loss were obtained for co-doping with Dy3+ and Nb5+. Besides, the Dy enrichment induced the formation of secondary phases, which were regarded as the low loss unit dispersed into the ceramic matrix, and largely facilitate the decreased dielectric loss. In particular, the analysis of temperature-dependent complex impedance spectra indicated that a stronger IBLC effect caused by the increased grain boundary resistance can also contribute to the optimized CP and low dielectric loss under appropriate contents of secondary phases.
Among the different types of multiferroic compounds, bismuth ferrite (BiFeO3; BFO) stands out because it is perhaps the only one being simultaneously magnetic and strongly ferroelectric at room ...temperature. Therefore, in the past decade or more, extensive research has been devoted to BFO-based materials in a variety of different forms, including ceramic bulks, thin films and nanostructures. Ceramic bulk BFO and their solid solutions with other oxide perovskite compounds show excellent ferroelectric and piezoelectric properties and are thus promising candidates for lead-free ferroelectric and piezoelectric devices. BFO thin films, on the other hand, exhibit versatile structures and many intriguing properties, particularly the robust ferroelectricity, the inherent magnetoelectric coupling, and the emerging photovoltaic effects. BFO-based nanostructures are of great interest owing to their size effect-induced structural modification and enhancement in various functional behaviors, such as magnetic and photocatalytic properties. Although to date several review papers on BFO and BFO-based materials have been published, they were each largely focused on one particular form of BFO. There have been very few papers addressing the different forms of BFO in a comprehensive manner and providing a comparison across the different forms. As BFO has been extensively studied over the past more than one decade especially in the past several years, there have been new phenomena arising more recently. Naturally they were not included in the early reviews. Here, we provide an updated comprehensive review on the progress of BFO-based materials made in the past fifteen years in the different forms of ceramic bulks, thin films and nanostructures, focusing on the pathways to modify different structures and to achieve enhanced physical properties and new functional behavior. We also prospect the future potential development for BFO-based materials in the cross disciplines and for multifunctional applications. We hope that this comprehensive review will serve as a timely updating and reference for researchers who are interested in further exploring bismuth ferrite-based materials.
Since the positive influences of defects on the performance of electroceramics were discovered, investigations concerning on defects and aliovalent doping routes have grown rapidly in the fields of ...inorganic chemistry and condensed matter physics. In this article, we summarized the types of defects in electroceramics as well as characterization tools of defects and highlighted the effects of intrinsic and extrinsic defects on the material performances with the emphasis on dielectric, ferroelectric, and piezoelectric properties. We mainly introduced defect related theoretical simulation and experimental results in several typical incipient ferroelectrics, ferroelectrics, and antiferroelectrics. Hence, the influences of defects on the crystal lattice were summed up, and then the main physical mechanisms were highlighted. Particularly, the performance enhancements of aliovalently doped electroceramics were also evaluated and reviewed. Finally, the outlook and challenges were discussed on the basis of their current developments. This article covers not only an overview of the state-of-the-art advances of defects and aliovalent doping routes in electroceramics but also the future prospects that may open another window to tune the electrical performance of electroceramics via intentionally introducing certain defects.
Colossal permittivity (CP) (εr=104~105) is attained in (A1/3Nb2/3)xTi1‐xO2 (A=Ba2+, Ca2+, Zn2+, Mg2+) ceramics. Here, (Ca1/3Nb2/3)xTi1‐xO2 material was studied as a typical example, and effects of Ca ...and Nb on their microstructure, dielectric properties and stability were studied. Both backscattering and elements mapping strongly confirmed the formation of secondary phases due to the addition of Ca and/or Nb. Secondary phases‐induced by Ca cannot affect dielectric properties of the ceramics when low Ca and Nb contents were doped, while secondary phases formed by Ca and Nb strongly affected their dielectric properties in a high doping level. In particular, their dielectric properties can be well modified by the optimization of sintering temperatures. In addition, the (Ca1/3Nb2/3)xTi1‐xO2 ceramics with x=0.01 exhibited the optimum dielectric properties (εr=130500 and tan δ=0.19). Electron‐pinned defect‐dipoles may be suitable to explain CP phenomenon of this work. We believed that this profound investigation can benefit the development of new TiO2 ceramics as a CP material.
Because of growing environmental concerns, the development of lead-free piezoelectric materials with enhanced properties has become of great interest. Here, we report a giant piezoelectric ...coefficient (d 33) of 550 pC/N and a high Curie temperature (T C) of 237 °C in (1–x–y)K1–w Na w Nb1–z Sb z O3– xBiFeO3– yBi0.5Na0.5ZrO3 (KN w NS z -xBF-yBNZ) ceramics by optimizing x, y, z, and w. Atomic-resolution polarization mapping by Z-contrast imaging reveals the intimate coexistence of rhombohedral (R) and tetragonal (T) phases inside nanodomains, that is, a structural origin for the R–T phase boundary in the present KNN system. Hence, the physical origin of high piezoelectric performance can be attributed to a nearly vanishing polarization anisotropy and thus low domain wall energy, facilitating easy polarization rotation between different states under an external field.
In this work, the quenched method can effectively promote the electrical properties of bismuth ferrite-barium titanate (BiFeO3BaTiO3, BFO-BTO) ceramics. Here we mainly focused on the modification of ...the quenched methods in the 0.67Bi1.05FeO3–0.33BaTiO3 ceramics with rhombohedral-cubic phase boundary. By optimizing the preparation conditions, the ceramics possess high Curie temperature (TC∼457 °C), large piezoelectricity (d33∼170 pC/N), and good ferroelectricity (Pr∼22 μC/cm2). The enhanced electrical properties are mainly assigned to the quenching technique with optimized conditions. We believe that such a systematic research can point out a way for further fabricating high-performance ceramics.
•Developing the quenched technique for fabricating Bi1.05FeO3BaTiO3 ceramics.•Attaining high TC (457 °C), large d33 (170 pC/N), and high Pr (22 μC/cm2).•Illuminating the physical mechanism for enhanced electrical properties.
Abstract
Multitudinous topological configurations spawn oases of many physical properties and phenomena in condensed-matter physics. Nano-sized ferroelectric bubble domains with various polar ...topologies (e.g., vortices, skyrmions) achieved in ferroelectric films present great potential for valuable physical properties. However, experimentally manipulating bubble domains has remained elusive especially in the bulk form. Here, in any bulk material, we achieve self-confined bubble domains with multiple polar topologies in bulk Bi
0.5
Na
0.5
TiO
3
ferroelectrics, especially skyrmions, as validated by direct Z-contrast imaging. This phenomenon is driven by the interplay of bulk, elastic and electrostatic energies of coexisting modulated phases with strong and weak spontaneous polarizations. We demonstrate reversable and tip-voltage magnitude/time-dependent donut-like domain morphology evolution towards continuously and reversibly modulated high-density nonvolatile ferroelectric memories.
Global environmental concerns on the toxicity of lead‐based piezoelectrics impel the great mass fervor on investigations of lead‐free alternatives. Barium titanate (BaTiO3, BT) ceramics, the first ...discovered perovskite ferroelectrics, were widely employed to fabricate dielectric capacitors from 1950s. Since a piezoelectric breakthrough was achieved via chemical modification, intensive researches have been performed embracing lead‐free BT‐based piezoelectrics and their extensional functionalities. In this review, we encompass the state‐of‐the‐art progress on chemical modification tuning phase structure toward advanced electrical properties in BT‐based ceramics. Generally, modulated regularity of cations substitution on phase transition is summarized and clarified. Then, we highlight the common methodologies of phase structure (phase boundary, relaxor phase, room‐temperature phase transition, etc.) design for optimizing piezoelectricity, electrostrictive strain, electrocaloric, dielectric energy storage or permittivity performances, and cover the noticeable developments and relevant physical mechanisms. Finally, perspectives and challenges on future research issues are featured. This review proposes to exert the significant guidance and service for material design of BT‐based and other lead‐free perovskite materials with superior functionalities.
Global environmental concerns on toxic lead‐based piezoelectrics impel the developments of lead‐freealternatives. This review covers the advanced progress on chemical modification tuning phase structuretoward superior piezoelectricity, electrostrictive strain, electrocaloric, dielectric energy storage andpermittivity performances in lead‐free barium titanate‐based ceramics. Generally modulated regularity ofcations substitution on phase transition is summarized. The common methodologies of phase structuredesign for optimizing electrical properties and the noticeable developments are highlighted. Finally,perspectives and challenges on future research issues are featured.
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