aoqing Xi

High and Temperature-Insensitive Piezoelectric Strain in Alkali Niobate Lead-free Perovskite

With growing concern over world environmental problems and increasing legislative restriction on using lead and lead-containing materials, a feasible replacement for lead-based piezoceramics is desperately needed. Herein, we report a large piezoelectric strain (d33*) of 470 pm/V and a high Curie temperature (Tc) of 243 °C in (Na0.5K0.5)NbO3-(Bi0.5Li0.5)TiO3-BaZrO3 lead-free ceramics by doping MnO2. Moreover, excellent temperature stability is also observed from room temperature to 170 °C (430 pm/V at 100 °C and 370 pm/V at 170 °C). Thermally stimulated depolarization currents (TSDC) analysis reveals the reduced defects and improved ferroelectricity in MnO2-doped piezoceramics from a macroscopic view. Local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrates the enhanced ferroelectricity and domain mobility from a microscopic view. Distinct grain growth and improvement in phase angle may also account for the enhancement of piezoelectric properties.

Electric field induced metastable ferroelectric phase and its behavior in (Pb, La)(Zr, Sn, Ti)O3 antiferroelectric single crystal near morphotropic phase boundary

Antiferroelectric (AFE) (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystal with composition near morphotropic phase boundary has been grown and studied. X-ray diffraction analysis and electrical properties reveal coexistence of antiferroelectric/ferroelectric (FE) phases, with the AFE phase dominated at room temperature. Temperature-dependent polarization and strain measurements indicate that the AFE phase can be induced into a metastable FE phase by electric field. The FE phase can be maintained in a wide temperature range above room temperature and recovers to AFE phase around a critical temperature of 90 °C, accompanied with remarkable change in field-induced strain. The strain at 90 °C (∼0.50%) is ten times larger than that at room temperature (∼0.04%), which makes the PLZST single crystal a promising candidate for thermal switch and actuator application.

Phase transitions and domain evolution in (Pb, La)(Zr, Sn, Ti)O3 single crystal

Antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystal has been grown and characterized. From dielectric measurements, x-ray diffraction analysis, and in situ observation of domain structures, we found two first-order phase transitions during heating from room temperature to 250 °C: orthorhombic (O) → rhombohedral (R) → cubic. Coexistence of O and R phases, with the R phase region strongly restricted inside the O phase matrix, has been observed within a broad temperature range above 123 °C. In addition, much denser domain walls appeared in the PLZST crystal when the O-R transition takes place.

Electric field induced phase transition and domain structure evolution in (Pb, La)(Zr, Sn, Ti)O3 single crystal

Antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystals with composition in the vicinity of morphotropic phase boundary have been grown and studied. From electric measurements, Raman study, and observation of domain structures, we found an electric field induced antiferroelectric to ferroelectric phase transition accompanied with fifteen times of strain difference. After this phase transition, the metastable ferroelectric phase (FEin) is preserved with soften of A1(TO1) mode and increase of long-range force. Coexistence of tetragonal (T) and rhombohedral (R) domains has been observed in virgin sample. Electric field induced T to R phase transition is verified by both extinction angle and domain morphology changes. Clamping “polar” structure formed by the embedded R phase would contribute to increase of long-range force. The remarkable strain difference accompany with induced phase transition makes the PLZST single crystal a promising candidate for electric switch and actuator applications.

Field induced phase transitions and energy harvesting performance of (Pb,La)(Zr,Sn,Ti)O3 single crystal

(Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with composition close to the morphotropic phase boundary had been grown by the flux method. The antiferroelectric-ferroelectric phase switching electric field was 0.8 kV/mm. Temperature-dependent dielectric and polarization versus electric field hysteresis loops revealed that the electric field induced ferroelectric phase could transform back into the antiferroelectric phase at depolarization temperature (145 °C). An enhanced pyroelectric coefficient value of 1.46 μC/cm2/K was obtained at 145 °C, which is several times larger than that of conventional pyroelectric materials. Furthermore, multiple peak pyroelectric responses and an enhanced harvested energy density value of 0.4 J/cm3 were achieved in the PLZST crystal. The enhanced harvested energy density and multiple peak pyroelectric responses make the PLZST crystal a promising candidate for high sensitive temperature sensors and energy conversion technologies.

Temperature-dependent terahertz magnetic dipole radiation from antiferromagnetic GdFeO3 ceramics

Temperature-dependent terahertz magnetic dipole radiation in antiferromagnetic GdFeO3 ceramic is investigated both theoretically and experimentally in this work. A two-level quantum transition mechanism is introduced to describe the excitation-radiation process, and radiative lifetime is derived analytically from the change of spin state density during this process. Terahertz spectral measurements demonstrate that the radiative frequency exhibits a red-shift and lifetime shortens as temperature increases, which is in good agreement with theoretical predictions. The temperature-sensitive radiative frequency and excellent terahertz emission mean that the antiferromagnetic ceramics show potential for application in terahertz sensors and frequency-tunable terahertz lasers.

A Mie resonant antenna with high sensitivity for force and strain measurement

We demonstrate the experimental and simulated performances of a Mie resonant antenna for force sensing with high sensitivity for compressive force and strain measurements inside soft materials. The proposed sensor is compatible with biological specimens and has small dimensions. It comprises a pair of dielectric cubes and an elastic layer of silicone rubber. The applied force is determined by measuring the redshift of the operating frequency when a mechanical load applied. Both simulated and experimental results demonstrate that the relationship between the frequency shift of the sensor and the applied compressive load could be fitted well using a quadratic equation with a maximum fitting error less than 17%, which enables highly sensitive telemetric force measurements to be performed inside structures by observing the operating frequency shift. The proposed design provides a simple and low-cost approach to realizing highly-efficient telemetric measurement inside soft materials such as biological tissues.

3D direct writing of terahertz metamaterials based on TbFeO3 dielectric ceramics

The integration of terahertz waves with metamaterials has become a key goal in modern photonics. In this work, we designed grating-structured metamaterials and face-centered-cubic (fcc) metamaterials based on TbFeO3 dielectric ceramics and built these materials using 3D direct writing technology. To simulate the behavior of the designed TbFeO3 metamaterials, the dielectric constant of TbFeO3 dielectric ceramic materials was determined. The desired strong electric and magnetic resonances were excited in the designed TbFeO3 metamaterials. The grating-structured metamaterials showed increased polarization-dependent transmittance as the line spacing decreased, while the fcc metamaterial showed a deep transmission dip at low frequencies and an electromagnetically induced increase in transmittance at higher frequencies. An increase in the electrical resistance contributed to the increase in the transmission properties of the fcc TbFeO3 metamaterial as its temperature decreased, while a reduction in the dielectric constant of TbFeO3 simultaneously caused a blueshift in this metamaterial. When combined with 3D direct writing technology, TbFeO3, with its high dielectric constant and low loss characteristics, represents an inexpensive and promising step towards the production of the next generation of low-cost, easy-to-fabricate, all-dielectric metamaterials.The integration of terahertz waves with metamaterials has become a key goal in modern photonics. In this work, we designed grating-structured metamaterials and face-centered-cubic (fcc) metamaterials based on TbFeO3 dielectric ceramics and built these materials using 3D direct writing technology. To simulate the behavior of the designed TbFeO3 metamaterials, the dielectric constant of TbFeO3 dielectric ceramic materials was determined. The desired strong electric and magnetic resonances were excited in the designed TbFeO3 metamaterials. The grating-structured metamaterials showed increased polarization-dependent transmittance as the line spacing decreased, while the fcc metamaterial showed a deep transmission dip at low frequencies and an electromagnetically induced increase in transmittance at higher frequencies. An increase in the electrical resistance contributed to the increase in the transmission properties of the fcc TbFeO3 metamaterial as its temperature decreased, while a reduction in the dielectr...

Dielectric meta-atom with tunable resonant frequency temperature coefficient

In this paper, we present a proof-of-concept of a new approach to achieving tailored resonant frequency temperature coefficients in dielectric meta-atoms. The technique involves introducing a thermally expanding or contracting material joining the active high permittivity dielectric absorbers. Both simulation and experiment show that by careful design of the element size and appropriate choice of thermomechanical intermediate layer material, increased or decreased resonant frequency shift temperature sensitivity is possible. Once the active dielectric material is chosen, and a meta-atom design determined, we show the resonant frequency shift depends on the thermal expansion coefficient of the intermediate layer. This work demonstrates the feasibility of manipulating the blue or red shift of metamaterial devices by introducing temperature responsive intermediate layers into meta-atoms.

Wear properties of microbeads prepared by colloidal injection moulding

Microbeads produced by colloidal injection moulding own high quality and performance. In this paper, friction and wear properties of the microbeads were studied. The effects of surface roughness, degassing of slurries, and water lubrication on the wear properties were discussed. The results show that the smoother the surface is, the better the wear resistance of the ceramic; the process of degassing of slurries in the moulding procedure improves the wear resistance of the ceramics; high load leads to severe wear under both dry sliding condition and water lubrication, and water acts as lubrication and decreases the wear of the ceramics.