Ferroelectric materials with large dielectric response and high temperaturestability have found significant applications in advanced electronics and electrical power/storage equipment. The effective approaches explored up to now mainly focus on improving dielectric response by employing the phase instability caused by the ferroelectric transition. Nevertheless, one inherent shortcoming is that the enhancement of dielectric permittivity is at the expense of the deterioration of its temperature stability. Here, a strategy that successfully achieves both enhanced dielectric response as well as excellent temperature reliability (with ε r ≈ 2 × 10 4 from 30 to 85 °C) by designing a laminated structure of tricritical ferroelectrics (LTF) with successive Curie temperatures is proposed. Moreover, the improvement in dielectric performance triggers the temperature-stable energy-storage performance as well as electrocaloric property in LTF specimens. Further microstructure investigation and phase-field modeling reveal that these remarkable properties of laminated layers originate from the successive occurrence of tricritical transition with a nanodomain structure in a wide temperature range. The findings may shed a new light on developing advanced ferroelectrics with high performance and thermal reliability.

Advanced ferroelectrics with a combination of large dielectric response and good temperature stability are crucial for many technologically important electronic devices and electrical storage/power equipment. However, the two key factors usually do not go hand in hand, and achieving high permittivity is normally at the expense of sacrificing temperature stability. This trade-off relation is eased but not fundamentally remedied using relaxor-type materials which are known to have a diffuse permittivity peak at their relaxor transition temperatures. Here, we report an anomalous trirelaxor phenomenon in a barium titanate system and show that it can lead to a giant dielectric permittivity (εr ≈ 18 000) over a wide temperature range (T span ≈ 34K), which successfully overcomes a long-standing permittivity–stability trade-off. Moreover, the enhancement in the dielectric properties also yields a desired temperature-insensitive electrocaloric performance for the trirelaxor ferroelectrics. Microstructure characterization and phase-field simulations reveal a mixture of tetragonal, orthorhombic, and rhombohedral polar nanoregions over a broad temperature window in trirelaxor ferroelectrics, which is responsible for this combination of giant dielectric permittivity and good temperature stability. This finding provides an effective approach in designing advanced ferroelectrics with high performance and thermal stability.

ever-increasing requirement for high energy density, [1][2][3][4] especially when incorporating with further material modification through nanocomposites, [7][8][9][10] blending, [11][12][13][14][15][16] laminated structure, [17][18][19][20][21] cross-linking, [22,23] and so on.Nevertheless, the state-of-the-art PVDF-based ferroelectric polymer usually exhibits mediocre temperature stability in energy storage performance, which cannot fully satisfy the applications at elevated temperature caused by the energy consumption or nearby heat sources. [24][25][26] These polymers commonly possess glass transition temperature (T g ) far below room temperature (as shown in Table S1, Supporting Information), which helps to enhance the energy density but sacrifices temperature stability. The molecular motion in ferroelectric polymers can be activated above T g , which promotes polar molecules orientation under external stimulus evidenced by a sudden increase of permittivity at T g . [23,27] Consequently, ultrahigh energy density (about 4-35 J cm −3 ) for PVDF-based polymers has always been reported at room temperature above T g . [1][2][3] On the other hand, low T g is detrimental to temperature stability of energy storage in PVDF showing dramatical degradation at elevated temperatures. Because rubbery-state amorphous region above T g , which manifests itself as loose chains with increased free volume, becomes vulnerable to temperature rise. [25,26,28] Recent investigations even point out that high-T g non-ferroelectric polymers can maintain an energy density around 0.5-1.8 J cm −3 up to a fairly high temperature. [25,26,29] Nonetheless, for ferroelectric polymers, it remains a considerable challenge to achieve high energy storage performance at the elevated temperature.In this work, we propose to design a strategy for stabilizing high energy density of ferroelectric polymer (PVDF) over a wide temperature range by blending with a miscible high-T g polymer (polymethyl methacrylate [PMMA]). The blending material forms a alternating lamellar structure consisting of high-polarization crystalline regions and mixed amorphous regions. It is found that this special morphology can induce a spatial confinement effect of chain mobility and structural change at elevated temperatures. Accordingly, the associated Thermal stability of polymer structure is a key to achieve stable energy density at elevated temperature for ferroelectric-polymer-based capacitors. Here, a poly (vinylidene fluoride) / polymethyl methacrylate (PMMA) blend with a stabilized spherulite structure displaying steady energy density around 7.8-9.8 J cm −3 across the temperature range up to 70 °C is reported, which outperforms most neat ferroelectric polymers at elevated temperature. The microstructure of the blend observed by atomic force microscopy exhibits an alternating lamellar structure (crystalline/mixed amorphous layers) within spherulites, which might be rationalized by PMMA being gradually expelled from the spherulite and finally staying between PVDF lamellae ...

Recently, tricritical ferroelectrics have been drawn tremendous attention, owing to their ultrahigh dielectric permittivities of up to εr > 5 × 104, and their consideration for prototype materials in the development of high-performance energy storage devices. Nevertheless, such a materials system suffers from the disadvantage of low breakdown strength, which makes its energy density far from the satisfactory level for practical application. In this paper, a material-modification approach has been reported, for improving the dielectric strength for tricritical ferroelectric materials Ba(Ti1−xSnx)O3 (BTS) through doping with Bi1.5ZnNb1.5O7 (BZN) additives. The results suggest that the electric strength has been largely improved in the modified tricritical ferroelectric material (BTSx-yBZN), and the associated energy density reaches Ue = 1.15 J/cm3. Further microstructure investigation indicates that the modified tricritical ferroelectric material exhibits homogenous fine grains with perovskite structure in crystal symmetry, and the BZN may help to form a special structure that could enhance the breakdown strength. The findings may advance the material design and development of high-energy storage materials.

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