Mupeng Zheng

Improving Dielectric Properties of PVDF Composites by Employing Surface Modified Strong Polarized BaTiO3 Particles Derived by Molten Salt Method

BaTiO3/polyvinylidene fluoride (BT/PVDF) is the extensive reported composite material for application in modern electric devices. However, there still exists some obstacles prohibiting the further improvement of dielectric performance, such as poor interfacial compatibility and low dielectric constant. Therefore, in depth study of the size dependent polarization and surface modification of BT particle is of technological importance in developing high performance BT/PVDF composites. Here, a facile molten-salt synthetic method has been applied to prepare different grain sized BT particles through tailoring the calcination temperature. The size dependent spontaneous polarizationof BT particle was thoroughly investigated by theoretical calculation based on powder X-ray diffraction Rietveld refinement data. The results revealed that 600 nm sized BT particles possess the strong polarization, ascribing to the ferroelectric size effect. Furthermore, the surface of optimal BT particles has been modified by water-soluble polyvinylprrolidone (PVP) agent, and the coated particles exhibited fine core-shell structure and homogeneous dispersion in the PVDF matrix. The dielectric constant of the resulted composites increased significantly, especially, the prepared composite with 40 vol % BT loading exhibited the largest dielectric constant (65, 25 °C, 1 kHz) compared with the literature values of BT/PVDF at the same concentration of filler. Moreover, the energy storage density of the composites with tailored structure was largely enhanced at the low electric field, showing promising application as dielectric material in energy storage device. Our work suggested that introduction of strong polarized ferroelectric particles with optimal size and construction of core-shell structured coated fillers by PVP in the PVDF matrix are efficacious in improving dielectric performance of composites. The demonstrated approach can also be applied to the design and preparation of other polymers-based nanocomposites filled with ferroelectric particles to achieve desirable dielectric properties.

Advanced FeTiNbO6/poly(vinylidene fluoride) composites with a high dielectric permittivity near the percolation threshold

FeTiNbO6 (denoted as FTN) is a recently discovered giant dielectric material with high Curie temperature (550 K). In this work, well dispersive FTN particles with mean particle size about 500 nm were synthesized by the improved solid-state reaction method. Using FTN particles as fillers and poly(vinylidene fluoride) (denoted as PVDF) polymer as matrix, multi-volume ratio (0%–60%) homogeneous ceramic/polymer composites have been prepared through a hot-pressing technology. At the same filling content, the FTN/PVDF composites display higher dielectric permittivity compared to the normal reported BaTiO3/PVDF composites, even larger than that of PVDF based composites using giant dielectric CaCu3Ti4O12 as filler. Especially, for 40 vol. % FTN/PVDF composites, the dielectric permittivity is as high as 181 measured at 100 Hz and 25 °C. Through the theoretical analysis correlated with structure evolution observation, it is deduced that the high dielectric performance originates from the combined effect of a variet...

Macroscopic ferroelectricity and piezoelectricity in nanostructured NaNbO3 ceramics

NaNbO3 sits at an instability between its ferroelectric and antiferroelectric phases, but its nanoscale polarization behavior is rarely reported. In this work, we produced high-density NaNbO3 nanostructured ceramics with a grain size of 50 nm by spark plasma sintering of nanocrystalline powder, which was obtained by mechanosynthesis. The nanostructured ceramics exhibited a symmetrical ferroelectric loop and increased relative permittivity. We believe that the increased internal stress at the nanoscale stabilized the ferroelectric domain structure, which promoted macroscopic piezoelectricity, demonstrating its potential uses in nanoelectromechanical systems.

High dense structure boosts stability of antiferroelectric phase of NaNbO3 polycrystalline ceramics

For NaNbO3, its intrinsic phase transition sequence is still controversial in literature. In this paper, high-densified NaNbO3 ceramics derived from mechanochemical nanostructures presented a stabilized antiferroelectric characteristic. In addition to the Tc of 360 °C, another diffuse dielectric anomaly appeared around 100 °C, which did not vanish after O2 annealing treatment. The fine structure analysis indicated that this dielectric anomaly belongs to first order phase transition from P phase to Q phase. Moreover, even exerting the strong electric field close to breakdown value, the normal ferroelectric loops cannot be induced, proving the large free energy difference between these two phases.

Normal-relaxor ferroelectric modulation of a-site complex perovskite ferroelectric (K1/2Bi1/2)TiO3 by post-annealing

In this work, the A-site complex perovskite K1/2Bi1/2TiO3 (KBT) was first found to demonstrate a normal-relaxor ferroelectric modulation by the annealing temperature. KBT ceramics were synthesized by the solid-state reaction method and subjected to a post-annealing at 800 °C or 1000 °C, respectively. It is found that the post-annealing at 800 °C switches KBT to a relaxor ferroelectric while the post-annealing at 1000 °C makes KBT develop into a normal ferroelectric. Besides, the sample annealed at 800 °C presented an inflection at 155 °C to decrease the Pr due to the enhanced relaxor behavior. Moreover, annealing at 1000 °C could promote the growth of the domains and the local ordering of A-site cations. It is believed that the modulation of KBT between the normal ferroelectric and relaxor was attributed to the domain size and the local ordering of A-site cations.

Topochemical build-up of BaTiO3 nanorods using BaTi2O5 as the template

One-dimensional BaTiO3 nanomaterials have important applications in nano-ferroelectric devices, and their high-quality synthesis is a hotspot in the field of chemistry of materials. In this work, single-crystalline perovskite BaTiO3 nanorods have been prepared by a two-step molten salt method. The conversion process and the topochemical mechanism were investigated based on XRD, DSC, SEM and TEM analysis. Firstly, one dimensional BaTi2O5 nanocrystallites have been synthesized in a molten environment and the self-polarization effect is responsible for the growth direction of [0 2 0]. Then, using these oriented BaTi2O5 monoclinic nanorods as templates, BaTiO3 perovskite nanorods have been further constructed through the topochemical reaction, in which all edge-sharing [TiO6] octahedra converted into corner-sharing modes to obtain the minimum energy state. One-dimensional morphology of BaTiO3 can only be obtained at a low calcination temperature, because at a high temperature, it will decompose into nanoparticles. This topological method is facile and can be developed to construct other orientated functional materials.

A highly dense structure boosts energy harvesting and cycling reliabilities of a high-performance lead-free energy harvester

Currently, effective piezoelectric energy harvesters are based on Pb(Zr,Ti)O3 (PZT) ceramics. However, the growing environmental concerns have been pushing the development of viable green alternatives for lead-based piezoelectric ceramics. In this study, a high quality Mn-modified (K0.5Na0.5)NbO3 (Mn-KNN) lead-free piezoelectric ceramic has been prepared, which is promising for use in lead-free piezoelectric energy harvesters. Herein, we showed that the 1.0 mol% Mn-KNN ceramics not only possessed high Curie temperature, but also exhibited excellent energy harvesting performance due to the highly dense fine-grained structure and various domain configurations. In the mode of a cantilever-type energy harvester, a high output power of 85 μW and peak-to-peak voltage of 16 V were obtained at the acceleration of 40 m s−2. Furthermore, the 1.0 mol% Mn-KNN energy harvester exhibits excellent fatigue resistance up to 106 cycles. These findings indicate potential applications of the Mn-KNN piezoelectric energy harvester for self-powered sources of wireless sensor network systems.

Delayed thermal depolarization of Bi0.5Na0.5TiO3-BaTiO3 by doping acceptor Zn2+ with large ionic polarizability

In this paper, (Bi0.5Na0.5)0.94Ba0.06Ti1-xZnxO3 ceramics (0 ≤ x ≤ 0.06) were prepared by the solid oxide reaction route. The doping of Zn2+ into Bi0.5Na0.5TiO3-6BaTiO3 delays the crossover from nonergodic to ergodic states, and the thermal depolarization temperature Td is delayed from 85 °C for pure samples to 120 °C for samples doped by 6% Zn2+, as confirmed by temperature-dependent dielectric and ferroelectric measurements. It suggests that the variation of the Td could be ascribed to the reformation of the long-range ferroelectric order due to the large ionic polarizability of Zn2+. The high ionic polarizability of Zn2+ can result in a large dipole moment of BO6 octahedra, thus strengthening the coherence of neighboring dipoles and suppressing the ferroelectric–relaxor transition. These results improve our understanding on the thermal depolarization of Bi0.5Na0.5TiO3-based ferroelectrics.

Ferroic characterizations, phase transformation, and internal bias field in 0.75Pb(Fe2/3W1/3)O3–0.25PbTiO3 multiferroic ceramic

The complex perovskite of 0.75Pb(Fe2/3W1/3)O3–0.25PbTiO3 (0.75PFW-0.25PT) ceramic was prepared by the conventional oxide mixing method. The detailed microstructure of 0.75PFW-0.25PT ceramic was investigated. At room temperature, the TEM analysis reveals that only cubic structure (nonpolar) exists, which is different from the phase coexistence of cubic (66%) and tetragonal (34%) structure revealed by XRD. A mechanism dominated by a temperature rise due to electron-beam irradiation has been proposed. The XPS measurement confirms the mixed balance state of Fe2+ and Fe3+ in the as-prepared 0.75PFW-0.25PT specimen, which facilitates the formation of the defect dipoles with oxygen vacancies, in turn resulting in the internal-bias field (Ei) phenomenon. The appearance of weak magnetic interactions is believed relating to the presence of noncompensated magnetic moments in Fe-rich islands. These results provide key information for understanding the composition, defect, ferroelectric, and ferromagnetic properties i...

The influence of A-site strontium ion in controlling the microstructure and electrical properties of P1−xSxZNZT ceramics

A Pb1−xSrx(Zn1/3Nb2/3)0.2(Zr0.5Ti0.5)0.8O3 (P1−xSxZNZT, 0.00 ≤ x ≤ 0.10) system was prepared through a conventional solid oxide process. Increasing addition of Sr2+ was found to induce a continuous decrease in grain size from 2.46 μm to 1.14 μm, accompanied by a phase transformation from coexisting rhombohedral and tetragonal phases to tetragonal phase only. The underlying mechanism of the evolution of dielectric and ferroelectric behavior in the P1−xSxZNZT ferroelectric ceramics was ascribed to the synergy between the grain size effect and the dilution of Pb-O covalency. Additionally, the grain size effect on domain wall displacement was found to be the main origin of the superior permittivity and piezoelectricity of the ceramics at intermediate grain size. The optimal electrical properties achieved for the P0.95S0.05ZNZT specimen at a grain size of about 1.79 μm, d33 = 465 pC/N, d33 × g33 = 11 047 × 10−15 m2/N make this material promising for multilayer energy harvesting device applications.