Xiangcheng Chu

Combined effect of preferential orientation and Zr/Ti atomic ratio on electrical properties of Pb(ZrxTi1−x)O3 thin films

Lead zirconate titanate [Pb(ZrxTi1−x)O3, PZT] thin films with various compositions, whose Zr/Ti ratio were varied as 40/60, 48/52, 47/53, and 60/40, were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel method. A seeding layer was introduced between the PZT layer and the bottom electrode to control the texture of overlaid PZT thin films. A single perovskite PZT thin film with absolute (100) texture was obtained, when lead oxide was used as the seeding crystal, whereas titanium dioxide resulted in highly [111]-oriented PZT films. The dielectric and ferroelectric properties of PZT films with different preferential orientations were evaluated systemically as a function of composition. The maximums of relative dielectric constant were obtained in the morphotropic phase boundary region for both (100)- and (111)-textured PZT films. The ferroelectric properties also greatly depend on films’ texture and composition. The intrinsic and extrinsic contributions to dielectric and ferroelectric properties were dis...

Single-crystal Nb-doped Pb(Zr,Ti)O3 thin films on Nb-doped SrTiO3 wafers with different orientations

Single-crystal Nb-doped Pb(Zr,Ti)O3 (PNZT) films were grown on electric conducting single-crystal Nb-doped SrTiO3 (Nb:STO) wafers by a sol-gel method. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PNZT film was formed on the {100} surface of the Nb:STO substrate, whereas [111]-oriented rhombohedral PNZT film on the {111} surface. The PNZT films on SrTiO3 substrates showed considerably high remnant polarization and low coercive field, as compared with conventional PZT films on Si wafers. In particular, high d33 value was obtained in the [001]-oriented PNZT films.

Coexistence of multiple positive and negative electrocaloric responses in (Pb, La)(Zr, Sn, Ti)O3 single crystal

The electrocaloric effect has been investigated in antiferroelectric (Pb, La)(Zr, Sn, Ti)O3 (PLZST) single crystals grown by the flux method. The measurements of polarization versus electric field loops on unpoled crystals revealed that at room temperature, a critical electric field of 1.8 kV/mm is needed to induce a ferroelectric phase from an antiferroelectric phase. The dielectric properties demonstrated that the induced ferroelectric phase recovers to antiferroelectric phase when temperature is above the depolarization temperature (70 °C–100 °C). Coexistence of the negative and positive electrocaloric effect has been achieved in ⟨001⟩-oriented PLZST single crystals. Multiple electrocaloric response values of −0.054 °C at room temperature, 0.17 °C near the depolarization temperature, −0.14 °C at 125 °C, and 0.75 °C around Curie temperature have been observed under an electric field of 3 kV/mm. The coexistence of multiple negative and positive electrocaloric effects in one material provides a possibilit...

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.

A screw-thread-type ultrasonic actuator based on a Langevin piezoelectric vibrator.

A novel screw-thread-type ultrasonic actuator based on a Langevin piezoelectric vibrator, with an assembly comprised a threaded shaft, is presented. The bolt-clamped Langevin vibrator consists of 4 chips of PZT ceramics and generates more energy with a certain input power. The threads of the stator multiply the linear force and position resolution, and the threaded rod is rotated directly to achieve linear movement without additional mechanical conversion. The actuator was designed and optimized using the Finite Element Method (FEM), and a prototype was fabricated. At 300 Vp-p, the maximum thrust force, velocity, and efficiency were approximately 4.2 N, 9.5 mm s(-1), and 5.6%, respectively.

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.

Crystal structure and dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 complex perovskite at microwave frequencies

The crystal structure and microwave dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 (0≤x≤1.0) solid solutions incorporated with 1 wt % CuO were investigated. Pure perovskite phases were formed in the whole composition range, and the crystal space group and unit cell volume of the perovskites were analyzed based on x-ray diffraction patterns. The configuration of octahedral tilting and the B-site ordering phase transition between x=0.9 and 1.0 were unambiguously assigned, respectively, to the corresponding superlattice diffractions. Moreover, the two important fingerprints A1g mode and F2g mode in Raman spectra, associated with the evolution of short range ordering and long range ordering of B-site cations, respectively, were further investigated by employing the full width at half-maximum and their Raman shifts to determine the degree of B-site ordering and the crystal bond strength in the perovskites. The microwave dielectric constants, quality factors, and temperature coefficients of re...

Characteristic analysis of an ultrasonic micromotor using a 3 mm diameter piezoelectric rod

Smart systems and devices generally use certain microstructures, e.g.?rod-?and strip-shaped structures. In this paper, a miniaturized piezoelectric rod is analysed using the finite element method (FEM) and a laser scanning vibrometer (LSV). The effects of some factors, including the detailed structure, material parameters and input voltage, on the resonant frequencies and vibration behaviors of a piezoelectric rod are studied. On the basis of experimental results, the vibration modes of the piezoelectric rod can be made available for use in fabricating an ultrasonic micromotor or piezoelectric actuators of other types. The prototype motor fabricated here has a maximum output torque of 410??N?m for a stainless steel stator and 360??N?m for a copper stator.

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.

Large d33 and enhanced ferroelectric/dielectric properties of poly(vinylidene fluoride)-based composites filled with Pb(Zr0.52Ti0.48)O3 nanofibers

Pb(Zr0.52Ti0.48)O3 (PZT) nanofibers with diameters of 150–200 nm are prepared via electrospinning and used as dielectric fillers in poly(vinylidene fluoride) (PVDF)-based composite films. Highly flexible polymer composite films are fabricated with a solution cast method. Enhanced dielectric constants are obtained at low volume fraction of PZT nanofibers. The orientation of PZT nanofibers perpendicular to the external electric field gives rise to improved dielectric breakdown strength. A subsequent uniaxial stretching of the composite films leads to higher crystallinity and breakdown strength of the polymer composites, which is favorable for the polarization of the nanocomposites at higher electric fields. Enhanced ferroelectric properties, i.e., higher saturated and remnant polarization, are obtained in these composite films. A high piezoelectric coefficient (d33) of ∼87.4 pm V−1 is also achieved for the polymer composite films filled with only 2.4 vol% of PZT nanofibers. The results show that the PZT/PVDF composite films have potential applications in piezoelectric sensors, and even piezoelectric actuators.