Guoxi Liu

Structure and negative thermal expansion in the PbTiO3–BiFeO3 system

The structures of (1−x)PbTiO3–xBiFeO3 (x=0.3 and 0.6) were investigated by means of the neutron powder diffraction. A splitting shift between Fe and Ti atoms was found along the c axis in 0.7PbTiO3–0.3BiFeO3; however, this splitting does not appear in 0.4PbTiO3–0.6BiFeO3. The tetragonal phase of PbTiO3–BiFeO3 exhibits a large spontaneous polarization. The negative thermal expansion of PbTiO3 is significantly enhanced in a wide temperature range by the BiFeO3 substitution. The average bulk thermal expansion coefficient of 0.4PbTiO3–0.6BiFeO3 is a¯v=−3.92×10−5°C−1, which is much strong in the known negative thermal expansion oxides.

Energy harvesting from ambient low-frequency magnetic field using magneto-mechano-electric composite cantilever

A magneto-mechano-electric (MME) composite cantilever for energy harvesting from ambient low-frequency magnetic field has been investigated in this study. The MME composite cantilever is made of a piezoelectric bimorph with NdFeB magnets attached at its tip. The properties of the MME composite cantilever based energy harvester were theoretically predicted by using the equivalent circuit model. The experimental results show that the maximum power density for excitations at the short- and open-circuit resonance frequencies (<100 Hz) is 11.73 μW/Oe2 cm3, which is one order of magnitude higher than that of previously reported magnetoelectric energy harvester. The research has proved the potential application of the composite cantilever for harvesting ambient low-frequency magnetic field energy.

A tunable ring-type magnetoelectric inductor

An electrostatically tunable magnetoelectric inductor made of ring-type Pb(Zr,Ti)O3(PZT)/MnZn ferrite/Pb(Zr,Ti)O3(PZT) laminated composite has been developed. This tunable inductor worked in converse magnetoelectric effect, and with applying an electric field of 3 kV/cm, it exhibited a large inductance tunability of up to 56.6% in a wide range of frequency. Such a large tunability in inductance was due to the strong electroelastomagnetic coupling between ferrite and piezoelectric layers. An analytical expression on the dependence of permeability μi on applied electric field E was also developed, which predicted the measured results well.

Colossal low-frequency resonant magnetomechanical and magnetoelectric effects in a three-phase ferromagnetic/elastic/piezoelectric composite

Colossal low-frequency resonant magnetomechanical (MM) and magnetoelectric (ME) coupling effects have been found in a three-phase composite made of Pb(Zr,Ti)O3 ceramic fibers/phosphor copper-sheet unimorph and NdFeB magnets. The experimental results revealed that the ferromagnetic/elastic/piezoelectric three-phase composite with a cantilever beam structure could show huge bending MM coefficient of ∼145.9 × 10−3/Oe (unit in bending radian per Oe) and ME voltage coefficient of ∼16 000 V/cm·Oe at the first-order bending resonance frequency of ∼5 Hz. The achieved results related to ME effect are at least one order of magnitude higher over those of other ME materials and devices reported ever. The extremely strong MM and ME couplings in the three-phase composite are due to strong magnetic force moment effect induced by the interaction between NdFeB magnets and the applied magnetic field, and further resonant enhancement via the strain-mediated phosphor copper-sheet with a relatively high mechanical quality factor.

Enhanced Resonance Magnetoelectric Coupling in (1‐1) Connectivity Composites

Bulk-magnetoelectric (ME) composites consisting of various piezoelectric and piezomagnetic materials with (3-0), (3-1), (2-2), and (2-1) connectivity are proposed in a bid to realize strong ME coupling for next-generation electronic-device applications. Here, 1D (1-1) connectivity ME composites consisting of a [011]-oriented Pb(Mg,Nb)O3 -PbTiO3 (PMN-PT) single-crystal fiber laminated with laser-treated amorphous FeBSi alloy (Metglas) and operating in L-T mode (longitudinally magnetized and transversely poled) are reported, which exhibit an enhanced resonant ME coupling coefficient of ≈7000 V cm-1  Oe-1 , which is nearly seven times higher than the best result published previously, and also a superhigh magnetic sensitivity of 1.35 × 10-13 T (directly detected) at resonance at room temperature, representing a significant advance in bulk magnetoelectric materials. The theoretical analyses based on magnetic-circuit and equivalent-circuit methods show that the enhancement in ME coupling can be attributed to the reduction in resonance loss of laser-treated Metglas alloy due to nanocrystallization and the strong magnetic-flux-concentration effect in (1-1) configuration composites.

A two degrees-of-freedom piezoelectric single-crystal micromotor

A two degrees-of-freedom (DOF) ultrasonic micromotor made of piezoelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal square-bar (dimensions 2 × 2 × 9 mm3) was developed. The PIN-PMN-PT square-bar stator can generate standing wave elliptical motions in two orthogonal vertical planes by combining the first longitudinal and second bending vibration modes, enabling it to drive a slider in two orthogonal directions. The relatively large driving forces of 0.25 N and motion speed of 35 mm/s were obtained under a voltage of 80 Vpp at its resonance frequency of 87.5 kHz. The proposed micromotor has potential for applications in micro robots, cell manipulators, and digital cameras as a two-DOF actuator.

A standing wave linear ultrasonic motor operating in in-plane expanding and bending modes.

A novel standing wave linear ultrasonic motor operating in in-plane expanding and bending modes was proposed in this study. The stator (or actuator) of the linear motor was made of a simple single Lead Zirconate Titanate (PZT) ceramic square plate (15 × 15 × 2 mm(3)) with a circular hole (D = 6.7 mm) in the center. The geometric parameters of the stator were computed with the finite element analysis to produce in-plane bi-mode standing wave vibration. The calculated results predicted that a driving tip attached at midpoint of one edge of the stator can produce two orthogonal, approximate straight-line trajectories, which can be used to move a slider in linear motion via frictional forces in forward or reverse direction. The investigations showed that the proposed linear motor can produce a six times higher power density than that of a previously reported square plate motor.

Morphotropic phase boundary and high temperature dielectric, piezoelectric, and ferroelectric properties of (1−x)Bi(Sc3/4In1/4)O3-xPbTiO3 ceramics

Piezoelectric ceramic (1 − x)Bi(Sc3/4In1/4)O3-xPbTiO3 (BSIPT) (0.45 ≤ x ≤ 0.70) solid solutions near the morphotropic phase boundary (MPB) were developed for high temperature piezoelectric transducer and actuator applications. It was found that the MPB composition of BSIPT ceramics was in the vicinity of x = 0.6, where it had relatively small tolerance factor t = 0.901 resulting in a high TC of 457 °C, and also optimal properties such as the high Pr = 25.4 μC/cm2, ɛr = 1153, d33 = 201 pC/N, kp = 0.34, and the low Ec = 23.5 kV/cm. Measurements also showed that the depoling temperature was 360 °C, about 200 °C higher than that of commercialized PZT ceramics, which indicated good temperature stability. BSIPT ceramics are promising candidates for high temperature applications.

A two-layer linear piezoelectric micromotor

A first bending (B1) mode two-layer piezoelectric ultrasonic linear micromotor has been developed for microoptics driving applications. The piezo-vibrator of the micromotor was composed of two small Pb(Zr,Ti)O3 (PZT-5) plates, with overall dimensions and mass of only 2.0 × 2.0 × 5.0 mm3 and 0.2 g, respectively. The proposed micromotor could operate either in single-phase voltage (standing wave) mode or two-phase voltage (traveling wave) mode to drive a slider via friction force to provide bidirectional linear motion. A large thrust of up to 0.30 N, which corresponds to a high unit volume direct driving force of 15 mN/mm3, and a linear movement velocity of up to 230 mm/s were obtained under an applied voltage of 80 Vpp at the B1 mode resonance frequency of 174 kHz.

A shear-bending mode high temperature piezoelectric actuator

A single ring-shape ceramic plate piezoelectric actuator operated in shear-bending mode was proposed for high-temperature operation. The actuator was formed from BiScO3-PbTiO3 ceramic and polarized in the radial direction. A large bending displacement at the center of the actuator was piezoelectrically generated under an applied voltage in the thickness direction due to axial-symmetric shear strain of the ring-shape configuration. The displacement obtained at 200 °C was about 20 μm, 11–14 times that of a normal piezoelectric plate of identical size.