Haosu Luo

Converse magnetoelectric effect in laminated composites of PMN-PT single crystal and Terfenol-D alloy

We have found experimentally and theoretically that laminated composites comprising one layer of length-magnetized Tb0.3Dy0.7Fe1.92 (Terfenol-D) magnetostrictive alloy sandwiched between two layers of thickness-polarized, electro-parallel-connected 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN–PT) piezoelectric single crystal have a large converse magnetoelectric effect characterized by a large magnetic induction in response to an applied ac voltage. The reported converse magnetoelectric effect originates from the product of the converse piezoelectric effect in the PMN–PT layers and the converse magnetostrictive effect in the Terfenol-D layer. Large converse magnetoelectric coefficient in excess of 105mG∕V is obtained in the composites at a low magnetic bias field of 170Oe. The measured magnetic induction has an excellent linear relationship to the applied ac voltage with amplitude varying from 50to160V. These made the composites to be a promising material for direct realization of core-free magnetic flux control de...

Bidirectional current-voltage converters based on magnetostrictive/piezoelectric composites

We report a power supply-free, bidirectional electric current-voltage converter based on a coil-wound laminated composite of magnetostrictive alloy and piezoelectric crystal. An electric current applied to the coil induces a magnetic field, resulting in an electric voltage from the composite due to the direct magnetoelectric effect. Conversely, an electric voltage applied to the composite produces a magnetic induction due to the converse magnetoelectric effect, leading to an electric current from the coil. The converter exhibits excellent linear relationships between current and voltage. Compared with traditional current/voltage converters made by operational amplifiers, the advantages of the proposed device include low cost, no power consumption, and bidirectional conversion.

Hydrogen-related dynamic dielectric behavior of barium titanate single crystals

Barium titanate single crystals had been placed in 0.01M NaOH solution to deposit hydrogen on their electrodes through the electrolysis of water. Two kinds of time-dependent changes in dielectric properties of the single crystals were observed: One occurred in the course of hydrogen deposition and the other lasted for a long period of time after the deposition. The diffusion of hydrogen and in and out of the single crystals may be the cause for the changes. This hydrogen-related dynamic dielectric behavior clearly shows that hydrogen is an important mobile ion other than oxygen vacancy in perovskite-type lattice. Extra attention should be paid to the role of hydrogen in time-dependent property changes, including resistance degradation and ferroelectric aging, of perovskite-type ferroelectric titanates.

Wavelength dependence of electro-optic effect in tetragonal lead magnesium niobate lead titanate single crystals

The refractive indices, birefringence, and linear electro-optic (EO) effect of 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 single crystals have been characterized as a function of wavelength. The dispersions of refractive indices for both ordinary and extraordinary rays were accurately described by a two-term Sellmeier dispersion equation, in which the parameters connected to the energy band structure were determined. A strong dispersion was found for birefringence and EO coefficient γc=γ33−(no∕ne)3γ13. With the increasing wavelengths, both of them decrease fast. The two-term Sellmeier dispersion model, in which one oscillator frequency is polarization dependent, was shown to represent closely all the results. The polarization potential, which specifies the magnitude of the oscillator frequency shift, was 0.40eVm4C−2.

LOCAL ELASTICITY RESPONSE IN FERROELECTRIC CRYSTALS STUDIED BY AFM-BASED NOVEL PROBE TECHNIQUES

ABSTRACT A novel probe technique, low frequency scanning probe acoustic microscope, was firstly developed based on the commercial atomic force microscope. The excitation frequency is in the range of several kHz up to teen-kHz, which is much lower than that in the conventional acoustic microscopes. The acoustic images of nanoscale domain structures in Pb(Mg1/3Nb2/3)O3-33%PbTiO3 single crystals were successfully visualized. Different electric polarizations show the variation of the elasticity in ferroelectrics, so the contrast of the acoustic images reflects the domain structure or the subsurface elasticity. In addition, the elasticity of the sample in response to the modulation of the excitation source is also discussed.

Cymbal actuators fabricated using PMN-PT single crystal

Abstract Cymbal actuators with very high displacement have been fabricated and tested. A cymbal actuator consists of a piezoelectric disc sandwiched between two truncated conical metal endcaps. Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystal is used as the piezoelectric driving element of the cymbal actuator. The influence of the piezoelectric coefficient of the driving element on the actuator performance has been studied. Due to its high piezoelectric d33 and d31 coefficients, a PMN-PT single crystal actuator gives a much higher displacement than a PZT actuator.

CONTRADIRECTIONAL TWO-WAVE MIXING IN RH-DOPED BATIO3 CRYSTAL

Contradirectional two-wave mixing (CTWM) in Rh-doped BaTiO3 crystal is investigated. The experimental results show that the energy transfer of CTWM has some distinctive characteristics different from forward two-wave mixing. Theoretical analysis of CTWM is presented in good agreement with the experimental observations. Both the experimental and theoretical studies show that the energy transfer direction of CTWM depends not only on the orientation of the crystal c axis and the sign of the light-induced carriers, but also on the electro-optic coefficients.

Study on self‐built optical path production in Ce‐doped BaTiO3 stimulated photorefractive scattering self‐pumped phase conjugator

The observations on the stimulated photorefractive scattering self‐pumped phase conjugator (SPS‐SPPC) in Ce‐doped BaTiO3 demonstrate that the self‐built pumped paths in the SPS‐SPPC are induced by the scattering seeds. Using these results, a formation mechanism of the SPS‐SPPC is presented, which is related to the scattering seeds, the contradirectional two‐wave mixing, and four‐wave mixing. The production conditions of the pumped paths are also given. The studies show that both too short and too long distances from the scattering seed to the region of the four‐wave mixing will bring about a failure in building the optical paths, and the large backscattering coefficient is always advantageous to produce these paths.

Transmission electron microscopy study of the domain structures of the relaxor ferroelectric PMN-PT 67/33 single crystals

Abstract The domain configurations of two different relaxor ferroelectric single crystals with the nominal composition (0.67)Pb(Mg⅓, Nb⅔)O3-(0.33)PbTiO3 (PMN-PT 67/33) grown by a modified-Bridgeman method were studied by transmission electron microscopy (TEM). The crystal structures of the samples were also investigated by X-ray diffraction (XRD). A TEM image recorded from one of the specimens along the [001] direction showed lamella-shaped 90° domains, indicating the presence of a tetragonal phase in PMN-PT 67/33. TEM images recorded from the second single crystal of PMN-PT 67/33 showed domains of irregular configurations and morphologies with orientations close to the <001> directions. Analysis indicates that the crystal with irregular domain configurations is rhombohedral. The thickness of the domains in the rhombohedral phase varies from one hundred to a few hundred nanometers. The domain patterns from this crystal indicate complicated angular relationships of 70.5°, 109.5° and 180° between the dipoles, which have possible orientations along the <111> directions.

High-field properties of PMN-PT single crystals

Electric properties of relaxor ferroelectric Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PMN-PT) single crystals near the rhombohedral-tetragonal transition under high-field phase boundary were studied. The single crystals in the <001> direction exhibited a remanent polarization of 30 /spl mu/C/cm/sup 2/, coercive field of 3.5 kV/cm and switchable polarization of 51 /spl mu/C/cm/sup 2/ at 9 kV/cm. The polarization-temperature dependence of the crystals indicated a reduction of 5% in the remanent polarization and 3.2% in switchable polarization at 80/spl deg/C. The remanent polarization decreased to 5 /spl mu/C/cm/sup 2/ at 146/spl deg/C (T/sub m/). However the switchable polarization fell to zero at that temperature. A loss of 12% in the polarization was observed in the switching cycles up to 2.5/spl times/10/sup 8/ reversals under bipolar pulse of 12 kV/cm. On the other hand, the crystals have a resistivity of 1.6/spl times/10/sup 9/ /spl Omega/-cm at 100/spl deg/C and with a electric field of 10 kV/cm. These results are favorable to applications for device design of the PMN-PT crystals.