Shiguang Yan

High charge-discharge performance of Pb0.98La0.02(Zr0.35Sn0.55Ti0.10)0.995O3 antiferroelectric ceramics

The energy storage performance and charge-discharge properties of Pb0.98La0.02(Zr0.35Sn0.55Ti0.10)0.995O3 (PLZST) antiferroelectric ceramics were investigated through directly measuring the hysteresis loops and pulse discharge current-time curves. The energy density only varies 0.2% per degree from 25 °C to 85 °C, and the energy efficiency maintains at about 90%. Furthermore, an approximate calculating model of maximum power density pmax was established for the discharge process. Under a relatively high working electric field (8.2 kV/mm), this ceramics possess a greatly enhanced power density of 18 MW/cm3. Moreover, the pulse power properties did not show degradation until 1500 times of charge-discharge cycling. The large released energy density, high energy efficiency, good temperature stability, greatly enhanced power density, and excellent fatigue endurance combined together make this PLZST ceramics an ideal candidate for pulse power applications.

Pulse discharge properties of PLZST antiferroelectric ceramics compared with ferroelectric and linear dielectrics

The pulse discharge properties of lead lanthanum zirconate stannate titanate (PLZST) antiferroelectric (AFE) ceramics, ferroelectric (FE) dielectrics, and linear dielectrics were compared in this paper. It is found that as the voltage increases, those three types of dielectrics display three different voltage-dependent regularities: the peak current (Imax) of linear dielectrics increases linearly with increasing voltage; the Imax of FE dielectrics rises up with a gradually declined increase rate; the Imax of PLZST AFE ceramics presents a three-stage growth and during the third stage, the regularity is similar with that of FE dielectrics. Furthermore, three advantages of PLZST AFE ceramics for pulse discharge can be determined: a large increase rate of Imax due the field-forced AFE-FE phase transition, a great enhanced power density and a relatively short discharge period time. These results would pave the way for understanding and utilizing AFE ceramics in pulse power application.

High temperature dielectric relaxation anomaly of Y3+ and Mn2+ doped barium strontium titanate ceramics

Relaxation like dielectric anomaly is observed in Y3+ and Mn2+ doped barium strontium titanate ceramics when the temperature is over 450 K. Apart from the conventional dielectric relaxation analysis method with Debye or modified Debye equations, which is hard to give exact temperature dependence of the relaxation process, dielectric response in the form of complex impedance, assisted with Cole-Cole impedance model corrected equivalent circuits, is adopted to solve this problem and chase the polarization mechanism in this paper. Through this method, an excellent description to temperature dependence of the dielectric relaxation anomaly and its dominated factors are achieved. Further analysis reveals that the exponential decay of the Cole distribution parameter n with temperature is confirmed to be induced by the microscopic lattice distortion due to ions doping and the interaction between the defects. At last, a clear sight to polarization mechanism containing both the intrinsic dipolar polarization and ex...

Pyroelectric response mechanism of barium strontium titanate ceramics in dielectric bolometer mode: The underlying essence of the enhancing effect of direct current bias field

Pyroelectric response mechanism of Ba0.70Sr0.30TiO3 ceramics under dielectric bolometer (DB) mode was investigated by dielectric and pyroelectric properties measurement. The variations of total, intrinsic, and induced pyroelectric coefficients (ptot, pint, pind) with temperatures and bias fields were analyzed. pint plays the dominant role to ptot through most of the temperature range and pind will be slightly higher than pint above T0. The essence of the enhancing effect of DC bias field on pyroelectric coefficient can be attributed to the high value of pint. This mechanism is useful for the pyroelectric materials (DB mode) applications.

Enhanced pyroelectric properties of Pb0.3Ca0.15Sr0.55TiO3 ceramic with first-order dominated phase transition under low bias field

We introduce a system of ferroelectric materials, Pb0.3CaxSr0.7-xTiO3 [PCST(x), x = 0.00, 0.05, 0.10, and 0.15], which exhibit good pyroelectric properties near room temperature. The enhanced field-induced pyroelectric coefficient of PCST(0.15) reached 81.8 × 10−8 C/cm2 K and it exhibited the largest voltage response with a dynamic black-body radiation measurement under a DC bias field of 200 V/mm. Systematic dielectric and phase transition analysis of the PCST(x) ceramics demonstrated that the phase transition gradually changed from a second-order to first-order dominated one with increasing Ca ion substitution. The enhanced pyroelectric properties under such a low bias field in the vicinity of room temperature of the PCST(0.15) ceramic are highly desirable for infrared detecting applications.

Colossal Negative Electrocaloric Effects in Lead-free Bismuth Ferrite-based Bulk Ferroelectric Perovskite for Solid-state Refrigeration

The electrocaloric effect (ECE) provides a novel route to realize eco-friendly cooling, whose cooling efficiency could be further enhanced by integrating the positive and negative ECE into one device. In contrast to the positive ECE that has been extensively achieved in ferroelectrics, few works have reported the negative ECE in lead-free polycrystalline solutions. In this work, a colossal negative ECE in lead-free bismuth ferrite-based systems is demonstrated for the first time. A record ECE in lead-free ferroelectric ceramic bulks, a ΔT of −2.0 °C and a ΔS of 1.9 J kg−1 K−1 measured directly by a heat flux sensor, is achieved, as well as large electrocaloric strength (ΔT/ΔE = −0.325 °C mm kV−1). The presence of short-range antiferrodistortive regions exhibiting non-polar states with average cubic symmetry may rationalize the large negative ECE in the system. The findings not only introduce a brand-new ferroelectric material into the negative ECE family but also may contribute to the design of phase structures of ferroelectrics for a giant negative ECE.

The novel dielectric relaxation behavior around the Curie point of (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics with giant effective permittivity

The temperature (80 K ~ 423 K) and frequency (40 Hz ~ 5 MHz) dependence of the permittivity were studied in (Ba0.7Sr0.3)0.96Y0.04TiO3 ceramics. A giant effective permittivity over 105 with a certain frequency and temperature stability and Debye-type dielectric relaxation behavior was observed. The complex impedance spectrum analysis reveals that the giant permittivity is due to the heterogeneous structure with a semiconducting bulk and high resistance electrode–ceramic interface. Deviating from low temperature (below 200 K) thermal activated behavior, the odd change of the characteristic relaxation frequency around the Curie point is observed and proven to be induced by the competition between the positive temperature coefficient of the resistance effect of the bulk ceramic and the dielectric anomaly of the surface layer capacitance, both of which originate from the ferroelectric–paraelectric phase transition.

Temperature and voltage stress dependent dielectric relaxation process of the doped Ba0.67Sr0.33TiO3 ceramics

The current decay characteristic in the time domain is studied in Y3+ and Mn2+ modified Ba0.67Sr0.33TiO3 ceramics under different temperatures (25 °C–213 °C) and voltage stresses (0 V–800 V). The decay of the current is correlated with the overlapping of the relaxation process and leakage current. With respect to the inherent remarkable dielectric nonlinearity, a simple method through curve fitting is derived to differentiate these two currents. Two mechanisms of the relaxation process are proposed: a distribution of the potential barriers mode around room temperature and an electron injection mode at the elevated temperature of 110 °C.