X. Z. Zhao

Enhanced magnetoelectric effect in Terfenol-D and flextensional cymbal laminates

A magnetoelectric (ME) laminate configuration was fabricated using a flextensional cymbal located between two magnetostrictive Terfenol-D (Tb1−xDyxFe2) plates. The laminate, operating in transverse magnetized/transverse polarized mode, has a ME voltage coefficient of 56.8mV∕Oe under a magnetic bias field of 1kOe, which is larger than that of conventional Terfenol-D/PZT/Terfenol-D configuration. It is believed that the enhancement of ME effect is due to the coupling between the magnetostriction of Terfenol-D and the high piezoelectric response of cymbal.

Effect of electron irradiation on poly(vinylidene fluoride–trifluoroethylene) 56/44 mol% copolymers

High-energy electron-irradiated poly(vinylidene fluoride?trifluoroethylene) 56/44?mol% copolymers are studied in a broad dose ranging from 0 to 110?Mrad. The experimental results are obtained by differential scanning calorimetry (DSC), x-ray diffraction, dielectric constant, dc conductivity and polarization hysteresis loop based on structural changes and dielectric relaxation behaviour. All the x-ray and DSC results show that both the crystalline and polar ordering decreased after irradiation, indicating a partial recovery from trans?gauche bonds to local trans bonds (polar ordering). The dielectric relaxation peaks, obeying the Vogel?Fulcher Law, indicate that the copolymers have transformed from a normal ferroelectric to a relaxor ferroelectric. It is also found that dc conductivity can be modulated with electron irradiation, as well as the hysteresis loop characteristics.

Influence of annealing on structural, electrical and optical properties of Dy-doped ZnO thin films

Transparent conductive Dy-doped zinc oxide thin films have been deposited on glass substrates by pulsed laser deposition technique. The effects of post-deposition annealing treatment on structural, electrical and optical properties of the ZnO : (Dy) thin films were investigated. The films show high transparency and conductivity. Van der Pauw measurements reveal that the films are n-type degenerate semiconductors. The electrical resistivity of the films deposited at 300 °C is 2.74 × 10−4 Ω cm with a carrier density of 9.33 × 1020 cm−3 and a Hall mobility of 24.48 cm2 V−1 s−1. The resistivity can be further reduced to as low as 2.12 × 10−4 Ω cm by post-deposition annealing at 420 °C for 2 h in nitrogen. Post-annealing increased the grain size and surface roughness of the films. The average transmission of the ZnO : (Dy) films (with a thickness about 529 nm) in the visible range is above 80%. The optical direct band gap value of the films is about 3.7 eV, which is slightly dependent on the annealing treatment in nitrogen.

Effect of patterned micro-magnets on superparamagnetic beads in microchannels

The trapping response of patterned micro-magnets (PMMs) was studied based on the parameters affecting superparamagnetic beads in microfluidic channels. Using replica moulding and electroplating technologies, the PMMs were fabricated on the microchannel bottom, which generated sufficient magnetic forces to bias the moments of magnetic particles in a flowing stream. A simplified physical principle was used to analyse the relative velocity of the magnetic particle in the confined space of a microchannel. The results revealed that the magnetic force contributed to the fluidic flow rate as well as to the hydrodynamic drag force. The relative velocity of magnetic particles was dependent on the frequency under an external magnetic field driven by an alternate current (ac) source. It showed that the magnetic gradient induced hysteresis characteristics of the transmission spectrum, associated with the interaction of superparamagnetic beads and magnetic field.

Study of domain boundary polarization in (111)-cut [Pb(Mg1∕3Nb2∕3)O3]0.7(PbTiO3)0.3 single crystal by piezoresponse force microscopy

Ferroelectric domain structure, especially the domain boundary polarization, in as-grown and poled (111)-cut PMN-30%PT single crystal has been studied by means of out-of-plane and in-plane piezoresponse force microscopies (PFMs). It revealed that the as-grown sample exhibits speckle-shaped microdomains, and the domain number distribution decreases exponentially as the domain size increases which can be described by the random field Ising model; in contrast, the poled sample shows stripe-shaped domains. Capacitive force-free PFM revealed a detailed domain boundary characteristic with net in-plane polarization. The presence of the in-plane polarization at the domain boundary also suggests the existence of orthorhombic phase in the rhombohedral matrix.

Reversible phase transition and structure memory effect of metastable phase in electron-irradiated poly(vinylidene-fluoride-trifluoroethyline) copolymers

We report the results of x-ray diffraction studies on phase transition behavior of irradiated poly(vinylidene-fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer. It is found that the transformations between the polar ferroelectric phase, the metastable paraelectric phase, and normal paraelectric phase induced by thermal and electric field are reversible. The reversible phase transition of the metastable paraelectric phase is very important to explain the appearance of giant strain in the irradiated P(VDF-TrFE) copolymer. The macroscopic strain caused by these reversible transitions was estimated.

Ultrasonic transducers using electron-irradiated vinylidene fluoride-trifluoroethylene copolymers

Single-element, planar transducers have been fabricated using electron-irradiated poly(vinylidene fluoride-trifluoroethylene) 80/20 mol% copolymers with different electron dosage. Electrical field-induced strain response of copolymer film with 100 Mrad dosage has been studied at 5 kHz and the electrostrictive coefficient was calculated. The transmitting response of the air-backing and epoxy-backing transducers was evaluated with the application of high DC bias voltages. Clear ultrasonic amplitudes and high frequency spectrum (>20 MHz) were observed when driven from a standard ultrasonic voltage source through a decoupling circuit. It has also showed that larger generation of ultrasonic waves will be induced under high DC bias field, which is due to the increase of induced d(33) piezoelectric coefficient. Two different polar bias voltages, positive and negative, were applied to the transducers and inverse waveforms were received, which was coincident with the theoretical analysis of the strain response of electrostrictive film.

Large magnetic heat transport in a Haldane chain material Ni(C3H10N2)2NO2ClO4

We report a study on the heat transport of an S = 1 Haldane chain compound Ni(C3H10N2)2NO2ClO4 at low temperatures and in magnetic fields. The zero-field thermal conductivities show a remarkable anisotropy for the heat current along the spin-chain direction (κb) and the vertical direction (κc), implying a magnetic contribution to the heat transport along the spin-chain direction. The magnetic-field-induced change of the spin spectrum has obviously opposite impacts on κb and κc. In particular, κb(H) and κc(H) curves show peak-like increases and dip-like decreases, respectively, at ∼9 T, which is the critical field that minimizes the spin gap. These results indicate a large magnetic thermal transport in this material.

Electron irradiation effects in electrostrictive P(VDF-TrFE) copolymers

Electrical field-induced strain response of electron-irradiated Poly(vinylidene fluoride trifluoroethylene) copolymer has been studied by a Mach-Zehnder type Heterodyne interferometer in the frequency range of 3 to 9 kHz. The electrostrictive constant is calculated from the strain results, which is of the same order of magnitude as those obtained at 1 Hz by a bimorph-based strain sensor, but at much lower electrical field. Changes in the piezoelectric coefficient, dielectric property and phase transition behavior of the same copolymer have been studied. The structural changes in the irradiated films were probed by means of differential scanning calorimetry, X-ray diffraction and IR spectra. The reversible solid-state transition between the polar and non-polar phase in the crystalline regions of the copolymer driven by the external electric field is suggested to be responsible for the significant high electrostrictive strain of the electron-irradiated copolymer.