Discovery of electric devil's staircase in perovskite antiferroelectric.

The devil's staircase, describing step-like function for two competing frequencies, is well known over a wide range of dynamic systems including Huyghens' clocks, Josephson junction, and chemical reaction. In condensed matter physics, the devil's staircase has been observed in spatially modulated structures, such as magnetic ordering. It draws widespread attentions because it plays a crucial role in the fascinating phenomena including phase-locking behaviors, commensurate-incommensurate phase transition, and spin-valve effect. Here, we report the observation of polymorphic phase transitions consisting of several steps in PbZrO3-based system-namely, electric devil's staircase-originated from competing ferroelectric and antiferroelectric interactions. We fully characterize a specific electric dipole configuration by decomposing this competitive interaction in terms of basic structure and modulation function. Of particular interest is that the occurrence of many degenerate electric dipole configurations in devil's staircase enables superior energy storage performance. These observations are of great significance for exploring more substantive magnetic-electric correspondence and engineering practical high-power antiferroelectric capacitors.

Entropy Enhanced Perovskite Oxide Ceramic for Efficient Electrochemical Reduction of Oxygen to Hydrogen Peroxide.

The electrochemical oxygen reduction reaction (ORR) offers a most promising and efficient route to produce hydrogen peroxide (H2 O2 ), yet the lack of cost-effective and high-performance electrocatalysts have restricted its practical application. Herein, an entropy-enhancement strategy has been employed to enable the low-cost perovskite oxide to effectively catalyze the electrosynthesis of H2 O2 . The optimized Pb(NiWMnNbZrTi)1/6 O3 ceramic is available on a kilogram-scale and displays commendable ORR activity in alkaline media with high selectivity over 91 % across the wide potential range for H2 O2 including an outstanding degradation property for organic dyes through the Fenton process. The exceptional performance of this perovskite oxide is attributed to the entropy stabilization-induced polymorphic transformation assuring the robust structural stability, decreased charge mobility as well as synergistic catalytic effects which we confirm using advanced in situ Raman, transient photovoltage, Rietveld refinement as well as finite elemental analysis.

Ion-Pair Engineering-Induced High Piezoelectricity in Bi4Ti3O12-Based High-Temperature Piezoceramics.

High-temperature piezoceramics are highly desirable for numerous technological applications ranging from the aerospace industry to the nuclear power sector. However, it is a grand challenge to achieve excellent piezoelectricity and high Curie temperature (Tc) simultaneously because there is a contradiction between the large piezoelectric coefficient and high Curie temperature in piezoceramics. Here, we provide a perspective via B-site ion-pair engineering to design piezoceramics with high performance for high-temperature applications. In bismuth-layered Bi4Ti2.93(Zn1/3Nb2/3)0.07O12 ceramics, high piezoelectricity of d33 = 30.5 pC/N (more than four times higher than that of pure Bi4Ti3O12 (d33 = 7.3 pC/N) ceramics) in conjunction with excellent thermal stability, high Curie temperature Tc = 657 °C, and large dc resistivity of ρ = 1.24 × 107 Ω·cm at 500 °C (three orders of magnitude larger than that of the pure Bi4Ti3O12 ceramics) are achieved by B-site Nb5+-Zn2+-Nb5+ ion-pair engineering. Excellent piezoelectricity is ascribed to sufficient orientation of the fine lamellar ferroelectric domain with the introduction of Nb5+-Zn2+-Nb5+ ion-pairs. The good temperature stability of d33 originates from the stability of the crystal structure and the robustness of the oriented ferroelectric domain. The significantly improved resistivity is due to the restricted mobility of oxygen vacancies. This work presents a brand-new technique for achieving high-temperature piezoceramics with high performance by B-site ion-pair engineering.

Atomic reconfiguration among tri-state transition at ferroelectric/antiferroelectric phase boundaries in Pb(Zr,Ti)O3.

Phase boundary provides a fertile ground for exploring emergent phenomena and understanding order parameters couplings in condensed-matter physics. In Pb(Zr1-xTix)O3, there are two types of composition-dependent phase boundary with both technological and scientific importance, i.e. morphotropic phase boundary (MPB) separating polar regimes into different symmetry and ferroelectric/antiferroelectric (FE/AFE) phase boundary dividing polar and antipolar dipole configurations. In contrast with extensive studies on MPB, FE/AFE phase boundary is far less explored. Here, we apply atomic-scale imaging and Rietveld refinement to directly demonstrate the intermediate phase at FE/AFE phase boundary exhibits a rare multipolar Pb-cations ordering, i.e. coexistence of antipolar or polar displacement, which manifests itself in both periodically gradient lattice spacing and anomalous initial hysteresis loop. In-situ electron/neutron diffraction reveals that the same parent intermediate phase can transform into either FE or AFE state depending on suppression of antipolar or polar displacement, coupling with the evolution of long-/short-range oxygen octahedra tilts. First-principle calculations further show that the transition between AFE and FE phase can occur in a low-energy pathway via the intermediate phase. These findings enrich the structural understanding of FE/AFE phase boundary in perovskite oxides.

Decoding the Double/Multiple Hysteresis Loops in Antiferroelectric Materials.

Antiferroelectric materials has become one of the most promising candidates for pulsed power capacitors. The polarization versus electric-field hysteresis loop is the key electrical property for evaluating their energy-storage performance. Here, we applied in situ biasing transmission electron microscopy to decode two representative energy-storage behaviors-namely, multiple and double hysteresis loops-in (Pb,La)(Zr,Sn,Ti)O3 system. Simultaneous structural examination and domain/defects observation establish a direct relationship between phase transitions and hysteresis loops. Sustaining a smaller period of modulated structure to a certain applied electric field and then undergoing additional transitions among varying antiferroelectric phases with increasing modulation periods before the final antiferroelectric-ferroelectric transition leads to the favorable multiple-loop configuration that realizes a high energy-storage performance. Such phenomenon is described by a model in terms of defect-driven phase transition. The distinctive mechanisms of multiple phase transition will inspire future composition-design for high switch-fielding antiferroelectric materials.

Enhancement of Energy-Storage Density in PZT/PZO-Based Multilayer Ferroelectric Thin Films.

PbZr0.35Ti0.65O3 (PZT), PbZrO3 (PZO), and PZT/PZO ferroelectric/antiferroelectric multilayer films were prepared on a Pt/Ti/SiO2/Si substrate using the sol-gel method. Microstructures and physical properties such as the polarization behaviors, leakage current, dielectric features, and energy-storage characteristics of the three films were systematically explored. All electric field-dependent phase transitions, from sharp to diffused, can be tuned by layer structure, indicated by the polarization, shift current, and dielectric properties. The leakage current behaviors suggested that the layer structure could modulate the current mechanism, including space-charge-limited bulk conduction for single layer films and Schottky emission for multilayer thin films. The electric breakdown strength of a PZT/PZO multilayer structure can be further enhanced to 1760 kV/cm, which is higher than PZT (1162 kV/cm) and PZO (1373 kV/cm) films. A recoverable energy-storage density of 21.1 J/cm3 was received in PZT/PZO multilayers due to its high electric breakdown strength. Our results demonstrate that a multilayer structure is an effective method for enhancing energy-storage capacitors.

Large magnetodielectric response of PST/LSMO/LCMO film over a wide temperature range.

Pb0.6Sr0.4TiO3/La0.7Sr0.3MnO3/La0.7Ca0.3MnO3 (PST/LSMO/LCMO) film is grown on Si substrate by chemical solution deposition method. The film crystallizes perfectly into perovskite phases with a random crystalline orientation. The La0.7Sr0.3MnO3/La0.7Ca0.3MnO3/Si layer exhibits low resistivity and obvious negative magnetoresistivity (MR); the PST/LSMO/LCMO film shows notable magnetocapacitance (MC) above 350 K, from 102.9% to 29.5%. Near room temperature, there is no distinguished magnetoelectric coupling; the MC is 34.3% @ 250 K, 29.5% @ 300 K and 32.8% @ 350 K respectively. The mechanism can be explained in light of the Maxwell-Wagner (MW) model and the enhanced MR origin from the successive mixed manganite phases and spin dependent tunneling across the junctions of PST/LSMO/LCMO. This work provides a new approach for designing and developing novel composites with promising MC.

Ferroelectric Ceramics for Pyroelectric Detection Applications: A Review.

Dynamic temperature sensing and infrared detection/imaging near room temperature are critical in many applications including invasive safety alarming, energy conversion, and public health, in which ferroelectric (FE) materials play an extremely important role due to their pyroelectricity. As a result, over the past few decades many efforts have been made to improve the understanding of pyroelectrics, explore new pyroelectric materials, and promote their practical applications. In this review, we consider the pyroelectric parameters and the two pyroelectric operation modes. Then based on the operation modes, we review recent achievements in the FE ceramic materials for pyroelectric detection applications, including Pb(Zr,Ti)O3-based, (Bi,Na)TiO3-based, (Sr,Ba)NbO3-based, Pb(Sc,Ta)O3-based, (Ba,Sr)TiO3-based, and Pb(Zr,Sn,Ti)O3-based systems. This review will attempt to provide guidance for further improvements of the pyroelectric properties of these materials and consider future exploration of new FE and other material candidates for use in temperature and infrared sensing/detection applications.

Effects of CuO addition on the sinterability and electric properties in PbNb2O6-based ceramics.

PbNb2O6 (PN)-based ceramics with tungsten bronze structure are promising piezoelectric materials in high-temperature devices such as piezoelectric vibration transducers. However, the PN-based ceramics usually exhibit a low bulk density, which greatly limits their practical applications. In this work, CuO was used as the sintering aid to form a liquid-phase bridge, leading to an obvious increase of the bulk density of PN-based ceramics by 11% (from 5.25 to 5.85 g cm-3) and the improvement of the piezoelectric constant (d 33) (from 168 to 190 pC/N) and the Curie temperature (T C) from 367 to 395 °C. The positive influence of CuO on densification has been proved by SEM and fracture toughness. The XRD patterns confirmed that there was no secondary phase introduced by CuO addition. The Raman spectra revealed that part of Cu2+ ions has probably diffused into host lattice of the PN and preferred to occupy on A-sites. These results not only demonstrate the high potential of the CuO added PN-based ceramics for high-temperature piezoelectric applications, but also reveal the corresponding structure-properties relationship as well as provide a way to improve the sinterability, d 33, and T C simultaneously.

Unveiling the ferrielectric nature of PbZrO3-based antiferroelectric materials.

Benefitting from the reversible phase transition between antiferroelectric and ferroelectric states, antiferroelectric materials have recently received widespread attentions for energy storage applications. Antiferroelectric configuration with specific antiparallel dipoles has been used to establish antiferroelectric theories and understand its characteristic behaviors. Here, we report that the so-called antiferroelectric (Pb,La)(Zr,Sn,Ti)O3 system is actually ferrielectric in nature. We demonstrate different ferrielectric configurations, which consists of ferroelectric ordering segments with either magnitude or angle modulation of dipoles. The ferrielectric configurations are mainly contributed from the coupling between A-cations and O-anions, and their displacement behavior is dependent largely on the chemical doping. Of particular significance is that the width and net polarization of ferroelectric ordering segments can be tailored by composition, which is linearly related to the key electrical characteristics, including switching field, remanent polarization and dielectric constant. These findings provide opportunities for comprehending structure-property correlation, developing antiferroelectric/ferrielectric theories and designing novel ferroic materials.

Lead-free (Ag,K)NbO3 materials for high-performance explosive energy conversion.

Explosive energy conversion materials with extremely rapid response times have broad and growing applications in energy, medical, defense, and mining areas. Research into the underlying mechanisms and the search for new candidate materials in this field are so limited that environment-unfriendly Pb(Zr,Ti)O3 still dominates after half a century. Here, we report the discovery of a previously undiscovered, lead-free (Ag0.935K0.065)NbO3 material, which possesses a record-high energy storage density of 5.401 J/g, enabling a pulse current ~ 22 A within 1.8 microseconds. It also exhibits excellent temperature stability up to 150°C. Various in situ experimental and theoretical investigations reveal the mechanism underlying this explosive energy conversion can be attributed to a pressure-induced octahedral tilt change from a - a - c + to a - a - c -/a - a - c +, in accordance with an irreversible pressure-driven ferroelectric-antiferroelectric phase transition. This work provides a high performance alternative to Pb(Zr,Ti)O3 and also guidance for the further development of new materials and devices for explosive energy conversion.

The phase structure and dielectric properties around a new type of phase boundary in a lead ytterbium niobite based solid solution.

The phase boundaries of dielectric materials have constantly been valuable for instructing the design of phase structures, revealing correlations between compositions and structures, and attaining the desired functional properties for piezoelectric, pyroelectric, electrostriction, electrocaloric, energy storage and energy harvesting applications. We here observe a new type of phase boundary in a solid solution of xPbTiO3·(1 - x)Pb(Yb1/2Nb1/2)O3 (x = 0.00-0.20), which is between an antiferroelectric (AFE) phase and a relaxor ferroelectric (RFE) phase. x = 0.10 is confirmed as the phase boundary. XRD, TEM, PFM and Raman spectroscopy analysis reveal two fundamental traits of the phase structure: (1) the polar state changes from AFE to FE order; and (2) the domain range evolves from micrometer-sized to nanometer-sized, both of which are normally separated but coexist around the phase boundary. The intriguing phase structure contributes to the distinctive dielectric properties: (1) a broad compositional zone (x < 0.10 and x ≥ 0.14) features low remnant polarization, low hysteresis and highly reversible domain wall motion, and is expected to be utilized for dielectric energy storage and electrostriction applications; and (2) a narrow nonergodic RFE zone (0.10 ≤ x < 0.14) demonstrates remnant and maximum polarization, co-dominated by composition and temperature, and has potential for pyroelectric and electrocaloric applications.

High electrostrictive properties and energy storage performances with excellent thermal stability in Nb-doped Bi0.5Na0.5TiO3-based ceramics.

As a promising candidate material replacing Pb(ZrTi)O3 (PZT), the lead-free Bi0.5Na0.5TiO3 (BNT) system exhibits outstanding piezoelectric and ferroelectric properties. However, the weak thermal stability of these electric properties hampers its practical applications. In this work, we designed and prepared novel Nb-doped 0.76Bi0.5Na0.5TiO3-0.24Bi0.5K0.5TiO3 (BNT-BKT) ceramics with superior temperature stability of electric properties. Both strain as well as discharging properties of 5% Nb-doped BNT-BKT ceramics varied less than 3% and 12.5% respectively from room temperature to 160 °C, ascribed to the enlarged gap between the depolarized temperature (T d or T F-R) and the maximum dielectric temperature (T m). In addition, we investigated the impacts of Nb doping on the phase transition, dielectric, piezoelectric and ferroelectric behaviors of BNT-BKT ceramics in detail. Temperature dependent dielectric spectrums indicated that T d decreased below room temperature with Nb modifying, revealing that the phase structure transformed from ferroelectric into ergodic relaxor. Accordingly, the maximum strain value of 0.21% and recoverable energy storage of 1.2 J cm-3 were simultaneously acquired at the critical composition of 5% Nb incorporation. Our results provide an effective means of obtaining BNT-based ceramics with simultaneously thermally stable strain and discharge properties for wide temperature actuator and capacitor applications.

Pseudo-spin model for the microtubule wall in external field.

Microtubules (MTs) in the cytoskeletons of eukaryotic cells provide a wide range of microskeletal and micromuscular functionalities. Some evidence has indicated that they can serve as a medium for intracellular signaling processing. In this paper, for the inherent symmetry structures and the electric properties of tubulin dimers, the microtubule (MT) is treated as a one-dimensional ferroelectric system. The nonlinear dynamics of the dimer electric dipoles is described by virtue of the double-well potential and the physical problem is further mapped onto the pseudo-spin system. In addition, the effect of the external electric field on the MT has been taken into account.