Yunfei Liu

Study on dielectric and magnetodielectric properties of Lu3Fe5O12 ceramics

Polycrystalline Lu3Fe5O12 ceramics with garnet structure were prepared by a solid-state reaction method. A dielectric relaxor behavior at low temperature was observed which may come from the dipolar effects associated with the charge carrier hopping between Fe2+ and Fe3+. It is noticeable that their magnetodielectric (MD) properties are excellent since the applied small magnetic fields can dramatically change the dielectric constants of Lu3Fe5O12 ceramics. The origin of the MD effect is discussed.

Multiferroic Properties of CoFe2O4/PbZr0-52Ti0.48O3 Composite Ceramics

The xCoFe 2 O 4 -(1−x)PbZr 0.52 Ti 0.48 O 3 (PZT) composite ceramics with x = 0.1, 0.2 and 0.3 have been prepared by solid state reaction method. X-ray diffraction result reveals that no chemical reaction or phase diffusion between the CoFe 2 O 4 and PZT phases exists in the composites. The composites exhibited ferroelectric as well as magnetic characteristics at room temperature. The distribution of the ferroelectric and magnetic domains has been observed by Scanning Probe Microscopy (SPM). The dielectric properties of the composite ceramics were also investigated. The dependence of dielectric properties and the morphology of both the ferroelectric and magnetic domains on CoFe 2 O 4 concentration were discussed in detail.

Optical properties of Bi3.15Nd0.85Ti3O12 nanostructures

Ferroelectric materials are widely researched because of their application in electronic devices. A ferroelectric nanotube is important both theoretically and experimentally because of its nonplanar structure. Bi3.15Nd0.85Ti3O12 nanotubes are fabricated utilizing templates of porous anodic aluminum oxide and thin films are synthesized as well for comparison. Atomic force microscopy, scanning electron microscopy, and x-ray diffraction reveal the microstructure of the samples. The optical properties are investigated carefully to reveal the size effect with the decrease in sample dimensionality. The observed shift of the absorption edge for different nanostructures is discussed.

Growth evolution and decay properties of the abnormally switched domains in LiNbO3 crystals

Direct domain writing is carried out in single-crystalline stoichiometric LiNbO3 crystals using a scanning probe microscope. The abnormally switched domains with polarization antiparallel to the poling field are observed, and their growth and decay processes are systematically studied. The radius of these domains is proportional to the pulse magnitude while it remains constant as the pulse width varies. These abnormal domains quickly decay, the lifetime of which is linear with the poling pulse magnitude while it stretched exponentially increases with the increasing pulse width. The experimental results are carefully discussed in relation to the reported charge injection model.

Drive frequency dependent phase imaging in piezoresponse force microscopy

The drive frequency dependent piezoresponse (PR) phase signal in near-stoichiometric lithium niobate crystals is studied by piezoresponse force microscopy. It is clearly shown that the local and nonlocal electrostatic forces have a great contribution to the PR phase signal. The significant PR phase difference of the antiparallel domains are observed at the contact resonances, which is related to the electrostatic dominated electromechanical interactions of the cantilever and tip-sample system. Moreover, the modulation voltage induced frequency shift at higher eigenmodes could be attributed to the change of indention force depending on the modulation amplitude with a piezoelectric origin. The PR phase of the silicon wafer is also measured for comparison. It is certificated that the electrostatic interactions are universal in voltage modulated scanning probe microscopy and could be extended to other phase imaging techniques.

Influence of feedback parameters on ferroelectric domain imaging with piezoresponse force microscopy

The piezoresponse (PR) amplitude and phase signals for antiparallel ferroelectric domains were investigated with different feedback parameters. It is found that the drive frequency and setpoint can strongly alternate the PR image contrast, while the drive phase can be considered as a constant adding to the PR phase signal. The PR amplitude is proportional to the drive amplitude while the PR phase is drive amplitude independent. The larger piezoelectric vibration amplitude and fitting piezoelectric constants (PCs) obtained by vectorial analysis compared with the known values are originated from the sample resonance, and the local electrostatic force can lead to a nonlinear shift in the measured PCs from the theoretical expectations.

Stress impact on dielectric properties of Bi3.15Nd0.85Ti3O12 films

Dielectric properties of Bi3.15Nd0.85Ti3O12 films under applied uniaxial stress were investigated. The results showed that the dielectric constant and loss increased with the stress changing from maximum compression (−70 MPa) to maximum tension (+70u2002MPa). Further studies discovered that the variation of the dielectric constant under stress was more distinct at higher testing ac field and ambient temperature. These observations were explained based on the domain wall movability related with the stress-induced domain reorientation.