Shenglin Jiang

Relaxor Ferroelectric‐Based Electrocaloric Polymer Nanocomposites with a Broad Operating Temperature Range and High Cooling Energy

Electrocaloric nanocomposites simultaneously derive high electrocaloric strength from inorganic inclusions and high dielectric strength from the polymer matrix to display a pronounced electrocaloric effect (ECE). By designing the inorganic filler and polymer matrix, which are both relaxor ferroelectrics with the ambient-temperature phase transition and minimized hysteresis, a large ECE becomes accessible with high cooling efficiency over a broad temperature range at and near room temperature.

Enhanced energy density of polymer nanocomposites at a low electric field through aligned BaTiO3 nanowires

In practical application, new dielectric capacitors with greater energy density at lower operating voltage will be promising candidates for high-performance electrical devices. Theoretically, it is possible to achieve large electric polarization at a low electric field via embedding aligned ferroelectric nanowires in a polymer matrix, which could release high energy density. However, in terms of practice, the design of nanocomposites with aligned nanowires poses a great technical challenge. Here, a new physical-assisted casting method was developed to tune the orientation of elongated BaTiO3 nanowires in a P(VDF-CTFE) matrix. In the Z-aligned nanocomposites, a large (Dmax − Pr) value of 9.93 μC cm−2 can be induced at a low electric field of 2400 kV cm−1 by aligning 3 vol% ferroelectric BaTiO3 nanowires in the poling direction. Compared with X–Y-aligned nanocomposites even at a high electric field of 3400 kV cm−1, the Z-aligned nanocomposites could exhibit simultaneously an enhanced energy density of 10.8 J cm−3 and a discharge efficiency of 61.4% at 2400 kV cm−1. To the best of our knowledge, among ferroelectric nanocomposites, this is the highest energy density ever obtained at such a low electric field. This work is of critical significance in making dielectric nanocomposites viable for energy storage devices in current electrical and electronic applications.

Significant influence of film thickness on the percolation threshold of multiwall carbon nanotube/low density polyethylene composite films

A series of multiwall carbon nanotube/low density polyethylene composite films with different thicknesses and different carbon nanotube volume fractions was prepared and studied. The result showed an interesting phenomenon which has not been reported before: when the thickness was reduced to the length range of the carbon nanotube filler, it could remarkably affect the percolation threshold of the composite films. Classical theories have been introduced to describe the phenomenon. This result could have significance in future applications of percolative composite thin/thick films.

Large enhancement of the electrocaloric effect in PLZT ceramics prepared by hot-pressing

In this contribution, we demonstrate the optimization of the microstructures of the Pb0.85La0.1(Zr0.65Ti0.35)O3 (PLZT) relaxor ferroelectric ceramics and subsequent enhancements in their polarization and electrical resistivity by using a hot-pressing process. The resulting superior breakdown strength of hot-pressed PLZT enables the application of high electric field to induce a giant electrocaloric effect, in which the adiabatic change of temperature (ΔT) and the isothermal change of entropy (ΔS) are around 2 times greater than those of the samples prepared by the conventional sintering approach using muffle furnace. Moreover, the addition of extra PbO to make up the loss of Pb in the high-temperature sintering leads to the further improvements in the phase composition and electrical properties of PLZT, due to inhibition of the pyrochlore phase formation. The relationship among the sintering conditions, the content of excess PbO, and the microstructure as well as the electrical characteristics of PLZT hav...

B site doping effect on depinning in Pb(Mn1/3Nb1/3Sb1/3)x(Zr0.825Ti0.175)1–xO3 ferroelectric ceramics

The polarization-field hysteresis (P-E) loops of Pb(Mn1/3Nb1/3Sb1/3)x(Zr0.825Ti0.175)1–xO3(PMnNSZT) ferroelectric ceramics show pinched shapes instead of the normal squarelike P-E loops in the range of 0.02≤x≤0.1. The pinched loops are assumed to be the result of the pinning effect of the defect dipoles. The absence of the pinched shape P-E loops can be attributed to the depinning resulting from strong p-type conductivity in PMnNSZT ceramics with high doping concentration of x>0.1. The x-ray photoelectron spectrum and x-ray diffraction investigations indicate that the p-type conductivity of the grain boundaries results from the aggregation of excessive B-site doping.

Enhanced antiferroelectric and electric-induced pyroelectric properties of Mn-substitued (Pb0.832Ba0.138La0.02)(Zr0.7Ti0.05Sn0.25)O3 ceramics

(Pb0.832Ba0.138La0.02)(Zr0.7Ti0.05Sn0.25)O3 ceramics with stable antiferroelectric phase at room temperature were fabricated by Mn doping. The enhancement of antiferroelectric phase is attributed that the substitution of Mn ion into the B site decreased tolerance factor of the ceramics. The largest pyroelectric figure of merit of 25 × 10−5 Pa−0.5 was obtained in (Pb0.832Ba0.138La0.02)(Zr0.7Ti0.05Sn0.25)O3 antiferroelectric ceramics with 0.2 mol. % Mn doping, which is far higher than that of convention phase transition materials. The increase of the pyroelectric response was attributed to the improvement in dc field-induced dielectric enhancement effect and the reduction in dielectric loss.

Piezoelectric and dielectric aging of Bi0.5(Na0.82K0.18)0.5TiO3 lead-free ferroelectric thick films

Ferroelectric Bi0.5(Na0.82K0.18)0.5TiO3 (NKBT) thick films have been prepared using screen printing on Pt electroded alumina substrates. The room-temperature dielectric constant of resulting 60 μm thick NKBT film reaches as high as 823 at 1 kHz and the depolarization temperature, Td, locates at 130 °C. The effect of amplitude and frequency of the applied ac field and the aging temperature as well as the Bi excess on the dielectric and piezoelectric aging characteristics are systemically studied. The results show that the dielectric and piezoelectric aging are associated with the reorientation of defect dipoles which stabilized the non-180° domain walls. By this reorientation the domain wall motions are clamped by a time dependent force resulting in the observed decrease in the dielectric and piezoelectric properties during the aging procedural. Moreover, the aging in NKBT thick films exhibits strong frequency dependence, which is caused by that the reorientation and alignment of the defect dipoles with th...

Ultrafast room temperature wiping-rubbing fabrication of graphene nanosheets as flexible transparent conductive films with high surface stability

In this letter, we developed an original innovative wiping-rubbing method to fabricate flexible transparent conductive films (TCFs) based on graphene nanosheets. We achieved this by using only commercial graphite block and polycarbonate film as raw materials, through a cost effective and ultrafast room temperature wiping-rubbing process (within 2 min). The properties of our flexible TCFs were competitive when comparing with literature reported graphene TCFs. Our flexible TCFs showed enough surface stability under a series of surface destructive treatments. The physical mechanism aspects of wiping-rubbing processes and surface stability were discussed.

Room temperature rubbing for few-layer two-dimensional thin flakes directly on flexible polymer substrates.

The functional layers of few-layer two-dimensional (2-D) thin flakes on flexible polymers for stretchable applications have attracted much interest. However, most fabrication methods are “indirect” processes that require transfer steps. Moreover, previously reported “transfer-free” methods are only suitable for graphene and not for other few-layer 2-D thin flakes. Here, a friction based room temperature rubbing method is proposed for fabricating different types of few-layer 2-D thin flakes (graphene, hexagonal boron nitride (h-BN), molybdenum disulphide (MoS2), and tungsten disulphide (WS2)) on flexible polymer substrates. Commercial 2-D raw materials (graphite, h-BN, MoS2, and WS2) that contain thousands of atom layers were used. After several minutes, different types of few-layer 2-D thin flakes were fabricated directly on the flexible polymer substrates by rubbing procedures at room temperature and without any transfer step. These few-layer 2-D thin flakes strongly adhere to the flexible polymer substrates. This strong adhesion is beneficial for future applications.

Large electric-induced pyroelectric properties in (Pb0.87La0.02Ba0.1) (Zr0.7Sn0.24Ti0.06)O3 antiferroelectric ceramics with excess PbO

(Pb0.87La0.02Ba0.1) (Zr0.7Sn0.24Ti0.06)O3 (PLBZST) antiferroelectric ceramics with the addition of 0–9 wt. % excess PbO were fabricated by the conventional solid-state reaction process, and their microstructure, dielectric, and pyroelectric properties were systemically investigated. When excess PbO content was less than 9 wt. %, two pyrochlore phases were formed along with the perovskite phase. Compared with common specimens, PLBZST antiferroelectric ceramics with excess PbO exhibited a higher pyroelectric coefficient and a lower dielectric loss, which are beneficial for the development of pyroelectric devices. Around the Curie temperature, as the excess PbO increased from 0 wt. % to 9 wt. %, PLBZST ceramics’ pyroelectric coefficient increased from 1600 μC/m2K to 4000 μC/m2K, and the figure of merit increased from 40 × 10−5 Pa−0.5 to 140 × 10−5 Pa−0.5 under a 400 V/mm dc field. The largest figure of merit of 200 × 10−5 Pa−0.5, which is about 8 times higher than that of conventional phase transition materi...