Papers by Keyword: Polarization Switching

Abstract: PbTiO₃ (PTO) films were successfully fabricated by sol-gel method. We studied the structure and the nanoscale polarization switching property using XRD and Piezoresponse Force Microscopy. The results reveal that the PTO films are single perovskite phase grain films with tetragonal structure, and are polycrystalline materials with no evidence of preferential orientation. The average grain size is about 150nm and a striped multi-domain structure is exhibited in individual grains. Under 15 kHz alternating current of PFM, a significant asymmetry of switching pattern was observed. We suggest that the cooperative action of the built-in electric field at the bottom interface and the PFM ac-voltage lead to the asymmetry switching.

Abstract: (111) preferred orientated ferroelectric PbZr0.3Ti0.7O3 (PZT) thin films with grain size of 300-500 nm, and root-mean-square (RMS) roughness of 2.927 nm were prepared by using radio frequency magnetron sputtering process. Piezoresponse force microscopy (PFM) has been used to write complex ferroelectric domain patterns using a biased sweeping PFM tip. Subsequent imaging of switched domain patterns was performed. The stabilization of the written domain was investigated by inverse biased tip scanning. The results indicate that these films are suitable for submicron scale domain writing, and the resulted domain are affected by the condition of crystalline boundary. The written domain is superficial and can be easily erased by inverse tip-applied electric field

Abstract: The polarization switching transients of spray-deposited ferroelectric (NH4)0.39K0.61NO3 (NKN) films have been investigated. Modified Sawyer-Tower circuit has been used to trace the hysteresis loop (P-E). The value of maximum polarization, Ps and coercive field, Ec was found to be 6.58 µC/cm2 and 4.10 kV/cm respectively. The polarization fatigue study has been carried out. The experimental polarization switching transients were fitted well with the Kolmogorov-Avrami-Ishibashi (KAI) nucleation theory The maximum polarization switching current (imax) and maximum switching time (tmax) have been measured as a function of the applied field. The activation field (), dimensionality (n) and switching time have been determined by employing the KAI model to the experimental switching transients. The atomic force microscopy (AFM) has been employed to estimate the grain size (~ 72 nm) and root mean square roughness (rms) (~ 130nm) of the (NH4)0.39K0.61NO3 films and has been correlated with the switching properties.

Abstract: In the current paper, a macroscopic differential model is constructed on the basis of the Landau theory of the first order phase transformation. Hysteresis loops and butterfly-shaped behaviors are modeled as a consequence of polarizations and orientation switchings. A non-convex free energy function is constructed to characterize different polarization orientations in the materials. Polarizations and orientation switchings are modeled by formulating the system state switching from one equilibrium state to another, as differential equations. The hysteresis loops and butterfly-shaped behaviors are successfully modeled. Comparison of the model results with the experimental counterpart is also presented.

Abstract: It is still an open problem how the thermal effect influences the fracture behavior of piezoelectric materials especially under cycling electrical loading. Experimental observations have found that the fracture toughness of piezoelectric solids under electric loading may be greatly different from that under mechanical loading. A pronounced rise of temperature may be caused either by mechanical or by electric loading. In this paper, the thermal effects and energy dissipation mechanism in cracked piezoelectric materials under cyclic-electric-loading have been studied. The temperature rise is derived under the assumption of decoupling between thermal and electromechanical fields and the influences of frequency and the shape of electric wave on the temperature rise are quantitatively analyzed.