Tongqing Yang

Dielectric measurement to probe electron ordering and electron-spin interaction

Here we found that dielectric measurement can be a sensitive probe to detect the behavior of electrons and electron-spin interaction in a strongly electron-correlated system. The CuO single crystal samples with and without excess holes were investigated by dielectric measurements in combination with magnetic susceptibility measurement. Only for the semiconducting single crystal with holes was dynamic dielectric relaxation with prominent frequency dispersion and large dielectric constants observed, suggesting localization of holes in the lattice. Coupling of hole and spin was directly observed by dielectric anomalies at the magnetic phase transitions. A pseudoferroelectric-like characteristic in the E–P plot was also observed. This study verifies that the holes are strongly coupled both to the vibrational and magnetic degrees of freedom in CuO. It also suggests the possibility of using dielectric measurement as a tool to investigate the coupling of electron and spin in strong correlated systems.

Temperature–electric field hysteresis loop of electrocaloric effect in ferroelectricity—Direct measurement and analysis of electrocaloric effect. I

The polarization of polar domain in ferroelectric materials is orientated and reversed with the alternating electric field, and the hysteresis loops of polarization-electric field (P-E) and strain-electric field (S-E) are observed. For electrocaloric (EC) effect, the temperature change with the application and removal of electric field is also attributed to the change of polarization with the applied field. In most reports about EC, the temperature change is shown as an abrupt jump or slump due to the applied electric field that is a pulsed wave. Obviously, it is impossible to observe the hysteresis loop of EC. In our research, both sine wave and pulsed wave electric field are applied to samples in direct measurement, and temperature-electric field hysteresis loop (T-E) is observed only in measurement of sine wave. The T-E hysteresis loop displays a shape of butterfly, just like the shape of S-E. The electric field dependence of EC is also given. The obtained results will be helpful for us to know the ele...

High recoverable energy density over a wide temperature range in Sr modified (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics with an orthorhombic phase

Via incorporation of Sr2+ into (Pb,La)(Zr,Sn,Ti)O3, high recoverable energy density (Ure) is achieved in (Pb,Sr,La)(Zr,Sn,Ti)O3 (PSLZST) ceramics. All Sr2+ modified ceramics exhibit orthorhombic antiferroelectric (AFE) characteristics, and have higher ferroelectric-AFE phase switching electric field (EA, proportional to Ure) than the base composition with a tetragonal AFE phase. By properly adjusting the Sr2+ content, the Ure of PSLZST ceramics is greatly improved. This is attributed to the substitution of Pb2+ by Sr2+ with a smaller ion radius, which decreases the tolerance factor leading to enhanced AFE phase stability and thus increased EA. The best energy storage properties are achieved in the PSLZST ceramic with a Sr2+ content of 0.015. It exhibits a maximum room-temperature Ure of 5.56 J/cm3, the highest value achieved so far for dielectric ceramics prepared by a conventional sintering technique, and very small energy density variation ( 4.9 J/cm3) over ...

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.

Vibration energy harvesting using a piezoelectric circular diaphragm array

Harvesting electric energy from mechanical vibration using a mechanically excited piezoelectric circular membrane array is presented in this paper. The piezoelectric circular diaphragm array is consisted of four plates with parallel connection, and the electrical characteristics of the array are examined under dynamic conditions. With an optimal load resistor of 11 kΩ, an output power of 27 mW was generated at 150 Hz under a pre-stress of 0.8 N force and a vibration acceleration of 9.8 m/s2. The results show that using a parallel array can increase significantly the output of energy compared with the use of a single plate.

Enhanced antiferroelectric stability and electric-field-induced strain properties in rare earth-modified Pb(Zr0.63Sn0.26Ti0.11)O3 ceramics

Pb0.97Ln0.02(Zr0.63Sn0.26Ti0.11)O3 ceramics with large electrically induced strain were fabricated by doping the base composition with rare earth ions. The enhancement of strain was because the substitution of rare earth ions for Pb2+ could decrease the tolerance factor of the ceramics and improve the stability of antiferroelectric phase. In addition, it was found that the electrically induced strain increased as the measuring frequency decreased; this was attributed to more complete domain reversal at the low frequency. The maximum electrically induced strain of 0.66% was obtained in Pb0.97Sm0.02(Zr0.63Sn0.26Ti0.11)O3 ceramics at the frequency 1 Hz.

Phase transition and electric field induced strain properties in Sm modified lead zirconate stannate titanate based antiferroelectric ceramics

The effect of Sm addition on the crystal structures and electrical properties of Pb1−3x/2Smx(Zr0.63Sn0.26Ti0.11)O3 ceramics were investigated in this work. X-ray diffraction analysis showed that with increasing Sm content from 0.005 to 0.03, the phase structure of the specimens underwent transition from ferroelectric (FE) to antiferroelectric (AFE) state due to the substitution of Sm3+ with smaller ion radius for Pb2+ decreasing the tolerance factor of the ceramics. In addition, it was observed that with the improvement of Sm3+ content, the strain of the specimens first increased and then decreased, and the largest value of 0.735% was obtained in the sample with x = 0.015 near AFE/FE phase boundary at the measuring frequency 1 Hz. This is because the reversal of the domains, which produces the strain, is more consummate in this composition. Further, the strain at different frequencies was nearly the same at high electric field, which was attributed to that the electric field applied to the sample was so large that the reorientation of the domains could finish in all measuring frequencies. Both a high strain level and a relatively good frequency stability in the specimen with x = 0.015 make a potential candidate for actuators applications over a wide-frequency working range.The effect of Sm addition on the crystal structures and electrical properties of Pb1−3x/2Smx(Zr0.63Sn0.26Ti0.11)O3 ceramics were investigated in this work. X-ray diffraction analysis showed that with increasing Sm content from 0.005 to 0.03, the phase structure of the specimens underwent transition from ferroelectric (FE) to antiferroelectric (AFE) state due to the substitution of Sm3+ with smaller ion radius for Pb2+ decreasing the tolerance factor of the ceramics. In addition, it was observed that with the improvement of Sm3+ content, the strain of the specimens first increased and then decreased, and the largest value of 0.735% was obtained in the sample with x = 0.015 near AFE/FE phase boundary at the measuring frequency 1 Hz. This is because the reversal of the domains, which produces the strain, is more consummate in this composition. Further, the strain at different frequencies was nearly the same at high electric field, which was attributed to that the electric field applied to the sample was so l...

Effects of glass additions on energy storage performance of (Pb0.97La0.02)(Zr0.92Sn0.05Ti0.03)O3 antiferroelectric thick films

50 μm-thick (Pb0.97La0.02)(Zr0.92Sn0.05Ti0.03)O3 antiferroelectric (AFE) thick films with different amount of 0.8PbO–0.2B2O3 glass additions were fabricated by the screen-printing method on alumina substrate, which was pre-coated with Pt as electrode. The effects of glass additions on dielectric properties and energy storage performance were investigated in details. Due to the enhancement of breakdown strength (BDS) of the specimens by the addition of glass, the energy storage performances of the thick films could be greatly improved. As a result, with 3% glass addition, the BDS of the specimens were as high as 475 kV/cm, the maximum polarization of 34.8 μC/cm2 and the maximum recoverable energy storage density of 7.4 J/cm3 were obtained. The results indicated the (Pb0.97La0.02)(Zr0.92Sn0.05Ti0.03)O3 (PLZST) thick films have a promising potential application in capacitors for pulsed power systems.

Investigation on behavior of the vibration-based piezoelectric energy harvester array in ultracapacitor charging

In this article, behaviors are investigated when the piezoelectric harvester array, consisting of four lead zirconate-titanate (PZT) circular diaphragms, charges ultracapacitors. It exhibits that V-I characteristic of the harvester array is approximately linear within 3RC, demonstrates that the array could be equivalent as the linear source. Relevant factors on ultracapacitor charging power P, including equivalent circuitry impedance R, charging capacitor C, operating frequency f, and connection patterns, are also studied. Meanwhile, interrelation between energy charging efficiency η and maximum charging power PMS is demonstrated, which is also used to find out the best condition for the harvester arrays operation. It exhibits that PZT harvester array connected in pattern of rectifying-parallel will have higher charging efficiency.

High antiferroelectric stability and large electric field–induced strain in MnO2-doped Pb0.97La0.02(Zr0.63Sn0.26Ti0.11)O3 ceramics

Crystal structure and electrical properties of MnO2-doped Pb0.97La0.02(Zr0.63Sn0.26Ti0.11)O3 antiferroelectric ceramic were studied in detail in this article. X-ray diffraction analysis showed that all specimens took on single tetragonal antiferroelectric structure, and antiferroelectric phase stability enhanced with the increase of MnO2 addition, which was because that the substitution of Mn2+ or Mn3+ with large ion radius for B-site Ti4+ decreased the tolerance factor of the ceramic. In addition, it was observed that different from Mn doping reducing Tm of ferroelectric ceramics, Tm of antiferroelectric ceramics increased with the addition of MnO2, which is for the reason that MnO2 addition enlarged the zone of antiferroelectric phase. Furthermore, by increasing MnO2 content, the strain first increased and then decreased. Meanwhile, the value improved obviously as the measuring frequency decreased. The largest electric field–induced strain of 0.65% was obtained in the specimen with 0.2 mol% MnO2 doping at the frequency of 1 Hz, which lay a foundation for preparing actuator with high strain energy density.