Antiferroelectric materials that display double ferroelectric hysteresis loops are receiving increasing attention for their superior energy storage density compared to their ferroelectric counterparts. Despite the good properties obtained in antiferroelectric La-doped Pb(Zr,Ti)O3 -based ceramics, lead-free alternatives are highly desired due to the environmental concerns, and AgNbO3 has been highlighted as a ferrielectric/antiferroelectric perovskite for energy storage applications. Enhanced energy storage performance, with recoverable energy density of 4.2 J cm-3 and high thermal stability of the energy storage density (with minimal variation of ≤±5%) over 20-120 °C, can be achieved in Ta-modified AgNbO3 ceramics. It is revealed that the incorporation of Ta to the Nb site can enhance the antiferroelectricity because of the reduced polarizability of B-site cations, which is confirmed by the polarization hysteresis, dielectric tunability, and selected-area electron diffraction measurements. Additionally, Ta addition in AgNbO3 leads to decreased grain size and increased bulk density, increasing the dielectric breakdown strength, up to 240 kV cm-1 versus 175 kV cm-1 for the pure counterpart, together with the enhanced antiferroelectricity, accounting for the high energy storage density.

Lead-Free Antiferroelectric Silver Niobate Tantalate with High Energy Storage Performance.

The last decade has witnessed a significant growth of research into materials with coupled magnetic and electric properties. Reviewed here are the main types and mechanisms of magnetoelectric interactions and conditions of their origin. Special attention is given to potentially practical materials that display magnetoelectric properties at room temperature. Example applications of magnetoelectric materials and multiferroics in information and energy saving technologies are discussed.

https://iopscience.iop.org/article/10.3367/UFNe.0182.201206b.0593/pdf

Magnetoelectric and multiferroic media

Recently, large electrocaloric effects (ECE) in antiferroelectric sol-gel PbZr0.95Ti0.05O3 thin films and in ferroelectric polymer P(VDF-TrFE)55/45 thin films were observed near the ferroelectric Curie temperatures of these materials (495 K and 353 K, respectively). Here a giant ECE (ΔT = 45.3 K and ΔS = 46.9 J K−1 kg−1 at 598 kV cm−1) is obtained in relaxor ferroelectric Pb0.8Ba0.2ZrO3 (PBZ) thin films fabricated on Pt(111)/TiOx/SiO2/Si substrates using a sol-gel method. Nanoscale antiferroelectric (AFE) and ferroelectric (FE) phases coexist at room temperature (290 K) rather than at the Curie temperature (408 K) of the material. The giant ECE in such a system is attributed to the coexistence of AFE and FE phases and a field-induced nanoscale AFE to FE phase transition. The giant ECE of the thin film makes this a promising material for applications in cooling systems near room temperature.

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A Giant Electrocaloric Effect in Nanoscale Antiferroelectric and Ferroelectric Phases Coexisting in a Relaxor Pb0.8Ba0.2ZrO3 Thin Film at Room Temperature

Lead-free dielectric ceramics with high recoverable energy density are highly desired to sustainably meet the future energy demand. AgNbO3-based lead-free antiferroelectric ceramics with double ferroelectric hysteresis loops have been proved to be potential candidates for energy storage applications. Enhanced energy storage performance with recoverable energy density of 3.3 J/cm3 and high thermal stability with minimal energy density variation (<10%) over a temperature range of 20-120 °C have been achieved in W-modified AgNbO3 ceramics. It is revealed that the W6+ cations substitute the B-site Nb5+ and reduce the polarizability of B-site cations, leading to the enhanced antiferroelectricity, which is confirmed by the polarization hysteresis and dielectric tunability. It is believed that the polarizability of B-site cations plays a dominant role in stabilizing the antiferroelectricity in AgNbO3 system, in addition to the tolerance factor, which opens up a new design approach to achieve stable antiferroelectric materials.

Silver Niobate Lead-Free Antiferroelectric Ceramics: Enhancing Energy Storage Density by B-Site Doping.

Phase Transitions in Ferroelastic and Co-Elastic Crystals

Quantum paraelectric SrTiO3 has resulted in many investigations because of the anomalous properties. Here, using the conventional solid-state reaction method, we fabricated polycrystalline SrTiO3 ceramics with pure cubic perovskite structure. A dielectric loss peak is observed at around 450 K and 100 Hz and it shifts to higher temperature with increasing frequency. The typical high-temperature dielectric relaxation process is confirmed to be related to the oxygen vacancies (OVs) inside ceramics. More interestingly, a Cole–Cole fitting to loss peaks reveals a weaker correlation among OVs for such dielectric materials compared with that of ferroelectrics.

Oxygen-vacancy-related high-temperature dielectric relaxation in SrTiO3 ceramics

Polycrystalline Lu3Fe5O12 ceramics with garnet structure were prepared by a solid-state reaction method. A dielectric relaxor behavior at low temperature was observed which may come from the dipolar effects associated with the charge carrier hopping between Fe2+ and Fe3+. It is noticeable that their magnetodielectric (MD) properties are excellent since the applied small magnetic fields can dramatically change the dielectric constants of Lu3Fe5O12 ceramics. The origin of the MD effect is discussed.

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Study on dielectric and magnetodielectric properties of Lu3Fe5O12 ceramics

Ho3Fe5O12 ceramics were fabricated by the solid-state reaction method. The results revealed an increase of the grain size, dielectric constant, and dielectric loss, while a decrease of the remnant magnetization and coercive field with increasing sintering temperature. A dielectric relaxation behavior was observed, which might be associated with the charge carrier hopping between Fe2+ and Fe3+. A cole–cole fitting to loss peaks revealed a dependence of the activation energy and the broaden factor on the relative density of the samples. Furthermore, at appropriate frequencies, the 1250 °C-sintered samples showed high dielectric constant, low dispassion, and good temperature stability around room temperature.

The effect of sintering temperature on magnetic and dielectric properties of Ho3Fe5O12 ceramics

Polycrystalline PbZrO3 films with a preferred orientation were fabricated via the metal-organic decomposition method. For heat-treated PbZrO3 films, the P-E hysteresis loops, dielectric spectra, and I-V curves show interesting changes with time, which strongly suggest the coexistence of antiferroelectric and ferroelectric phases at room temperature. Based on the easy transition between these two phases, the electric properties of the films become tunable. A dielectric tunability of about 50.2% below 8.2 V makes it a promising low working-voltage dielectric tunable material, and the significant current change of four orders of magnitude indicates potential application as a voltage-controlled rheostat.

Tunable electric properties of PbZrO3 films related to the coexistence of ferroelectricity and antiferroelectricity at room temperature

The drive frequency dependent piezoresponse (PR) phase signal in near-stoichiometric lithium niobate crystals is studied by piezoresponse force microscopy. It is clearly shown that the local and nonlocal electrostatic forces have a great contribution to the PR phase signal. The significant PR phase difference of the antiparallel domains are observed at the contact resonances, which is related to the electrostatic dominated electromechanical interactions of the cantilever and tip-sample system. Moreover, the modulation voltage induced frequency shift at higher eigenmodes could be attributed to the change of indention force depending on the modulation amplitude with a piezoelectric origin. The PR phase of the silicon wafer is also measured for comparison. It is certificated that the electrostatic interactions are universal in voltage modulated scanning probe microscopy and could be extended to other phase imaging techniques.

Song Peng

Papers

Oxygen-vacancy-related high-temperature dielectric relaxation in SrTiO3 ceramics

Study on dielectric and magnetodielectric properties of Lu3Fe5O12 ceramics

The effect of sintering temperature on magnetic and dielectric properties of Ho3Fe5O12 ceramics

Tunable electric properties of PbZrO3 films related to the coexistence of ferroelectricity and antiferroelectricity at room temperature

Drive frequency dependent phase imaging in piezoresponse force microscopy