Nai-Ben Ming

Substitution-induced phase transition and enhanced multiferroic properties of Bi1−xLaxFeO3 ceramics

Single-phase, insulating Bi1−xLaxFeO3 (BLFOx, x=0.05, 0.10, 0.15, 0.20, 0.30, and 0.40) ceramics were prepared. An obvious phase transition from rhombohedral to orthorhombic phase was observed near x=0.30. It is found that the phase transition destructs the spin cycloid of BiFeO3 (BFO), and therefore, releases the locked magnetization and enhances magnetoelectric interaction. As a result, improved multiferroic properties of the BLFO0.30 ceramics with remnant polarization and magnetization (2Pr and 2Mr) of 22.4μC∕cm2 and 0.041emu∕g, respectively, were established.

Ferroelectric-field-effect-enhanced electroresistance in metal/ferroelectric/semiconductor tunnel junctions

We propose a tunneling heterostructure by replacing one of the metal electrodes in a metal/ferroelectric/metal ferroelectric tunnel junction with a heavily doped semiconductor. In this metal/ferroelectric/semiconductor tunnel diode, both the height and the width of the tunneling barrier can be electrically modulated due to the ferroelectric field effect, leading to a colossal tunneling electroresistance. This idea is implemented in Pt/BaTiO3/Nb:SrTiO3 heterostructures, in which an ON/OFF conductance ratio above 10

Enhancement of second‐harmonic generation in LiNbO3 crystals with periodic laminar ferroelectric domains

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The growth striations and ferroelectric domain structures in Czochralski-grown LiNbO3 single crystals

can be readily achieved at room temperature. The colossal tunneling electroresistance, reliable switching reproducibility and long data retention observed in these ferroelectric tunnel diodes suggest their great potential in non-destructive readout nonvolatile memories.Ferroelectric tunnel junctions (FTJs), composed of two metal electrodes separated by an ultrathin ferroelectric barrier, have attracted much attention as promising candidates for non-volatile resistive memories. Theoretical and experimental works have revealed that the tunnelling resistance switching in FTJs originates mainly from a ferroelectric modulation on the barrier height. However, in these devices, modulation on the barrier width is very limited, although the tunnelling transmittance depends on it exponentially as well. Here we propose a novel tunnelling heterostructure by replacing one of the metal electrodes in a normal FTJ with a heavily doped semiconductor. In these metal/ferroelectric/semiconductor FTJs, not only the height but also the width of the barrier can be electrically modulated as a result of a ferroelectric field effect, leading to a greatly enhanced tunnelling electroresistance. This idea is implemented in Pt/BaTiO3/Nb:SrTiO3 heterostructures, in which an ON/OFF conductance ratio above 10(4), about one to two orders greater than those reported in normal FTJs, can be achieved at room temperature. The giant tunnelling electroresistance, reliable switching reproducibility and long data retention observed in these metal/ferroelectric/semiconductor FTJs suggest their great potential in non-destructive readout non-volatile memories.

Ferroelectric properties of Bi3.25La0.75Ti3O12 thin films prepared by chemical solution deposition

Using the Czochralski method we have grown LiNbO3 crystals with periodic laminar ferroelectric domains whose half‐period nearly corresponds to the coherence length. Quasi‐phase‐matching for the nonlinear optical coefficient d33 has been approximately realized and enhancement of second‐harmonic generation relative to conventionally phase‐matched crystals of the same length has been observed.

Electro-optic effect of periodically poled optical superlattice LiNbO3 and its applications

The rotational striations and power striations are studied in LiNbO3 crystals and one-to-one correspondence between the striations and temperature fluctuations is demonstrated. The ferroelectric domain structures related to the rotational striations and the power striations have been observed. The distribution of solute concentration in rotational striations is measured by means of energy dispersive X-ray analysis in the scanning electron microscope, and it has been concluded that the ferroelectric domain structures depend on the solute concentration gradient.

Preparation of monodisperse polystyrene spheres in aqueous alcohol system

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films were prepared on platinum coated silicon substrate by chemical solution deposition. The layered-perovskite phase was obtained by rapid thermal annealing the spin-on films at 650 or 700 °C for 180 s. Scanning electron micrographs showed uniform surfaces composed of spherical grains. The grain size increased with increasing annealing temperature. The remanent polarization and coercive field of 650 °C annealed film were 12.3 μC/cm2 and 48.9 kV/cm, respectively, and those of 700 °C annealed films were 18.2 μC/cm2 and 51.1 kV/cm. BLT thin films showed little polarization fatigue under 250 kV/cm bipolar cycling at 50 kHz, while fatigue properties deteriorated with decreasing cycling field and frequency. At various frequencies from 1 Hz to 50 kHz, nonvolatile polarization Pnv showed nearly no degradation over an initial period of cycling, then decayed logarithmically with switching cycles. The onset of logarithmic decay of Pnv was found to increase linearly with ...

LiTaO3 crystal periodically poled by applying an external pulsed field

The electro-optic effect of periodically poled optical superlattice LiNbO3 (PPLN) was studied. Because of the periodic electro-optic (EO) coefficient, the reciprocal vector of the periodic structure can be used to compensate for the phase mismatch between the ordinary and extraordinary waves, which is similar to the nonlinear optical frequency conversion process. If the quasi-phase-matching condition is satisfied, polarization of a light propagated in PPLN can rotate linearly with the applied electric field, which shows that PPLN may be used as a precise spectral filter or an EO switch.

Processing- and composition-dependent characteristics of chemical solution deposited Bi 4−x La x Ti 3 O 12 thin films

The aqueous methanol/ethanol/n-propyl systems have been exploited as dispersion medium in emulsion polymerizing of polystyrene (PS) using sodium lauryl sulfate and potassium persulfate as emulsifier and initiator, respectively. The diameter of PS spheres synthesized in aqueous methanol/ethanol/n-propyl dispersion media is 80 nm–1.15 Am/150 nm–1.3 Am/260 nm–1.65 Am. The replacement of water dispersion medium with alcohol dispersion medium can lift the upper limit of PS spheres size from 1 to 1.65 Am. A seeded growth technique based on aqueous alcohol dispersion media was developed to improve spheric-shape and monodispersity as well as increasing PS spheres size. In this technique, the styrene added for the growth of seeds is diluted with four times volume absolute alcohol, which makes the swelling process of styrene in seed (which is necessary in the conventional two-step seed growth technique) unnecessary and consequently reduces dramatically the synthesis time. D 2003 Elsevier Science B.V. All rights reserved.

Characteristics of LaAlO3 gate dielectrics on Si grown by metalorganic chemical vapor deposition

A method of periodically poling LiTaO3 single crystal at room temperature by applying an external pulsed field is proposed. The relationship between the growth of inverted domains and switching current as well as switching time has been studied. The growth of inverted domains can be controlled by the duration of the pulsed field. The domain structure with period Λ≳8 μm has been fabricated in a 0.3‐mm‐thick plate of LiTaO3 by partial switching.