Characterization ferroelectric materials

To characterize ferroelectric materials usually the dependence of the polarization on the applied voltage is measured by means of a Sawyer-Tower circuit or by recording the current response to a voltage step. The / (V/)-hys(crcsis curve is used to determine the remanent polarization and coercive voltage, respectively coercive field. These two parameters are of critical importance to the design of external circuits of FeRAMs. 

As a ferroelectric material, each piezoelectric ceramic is characterized by a Curie point or Curie temperature, T (Jaffe et al., 1971). Above this temperature, the ferroclcctricity is lost. An irreversible degradation of the... 

At high temperatures, ferroelectric materials transform to the paraelectric state (where dipoles are randomly oriented), ferromagnetic materials to the paramagnetic state, and ferroelastic materials to the twin-free normal state. The transitions are characterized through order parameters (Rao Rao, 1978). These order parameters are characteristic properties parametrized in such a way that the resulting quantity is unity for the ferroic state at a temperature sufficiently below the transition temperature, and is zero in the nonferroic phase beyond the transition temperature. Polarization, magnetization and strain are the proper order parameters for the ferroelectric. 

Polarization of a ferroelectric material varies nonlinearly with the applied electric field. The P-E behaviour is characterized by a hysteresis loop and observation of the hysteresis loop is the best evidence for the existence of ferroelectrcity in a material. The hysteresis loop has its origin in the rearrangement of domains under the influence of an applied elecric field. Generally, the domains are randomly distributed, giving a net zero polarization. Under an applied field or mechanical stress, favourably oriented domains... 

The optical properties of ferroelectric materials are characterized by birefringence. Barium titanate is isotropic only in the cubic phase. The tetragonal and the rhombohedral phases are... 

Y. Rosenwaks, M. Molotski, A. Agronin, P. Urenski, M. Schvebelman, and G. Rosenman, Nanoscale characterization of ferroelectric materials. Scanning force microscopy approach, Eds. M. Alexe, A. Guverman, Springer, 2004. 

Recently, ferroelectric materials, especially in thin film form, have attracted the attention of many researchers. Their large dielectric constants make them suitable as dielectric layers of microcapacitors in microelectronics. They are also investigated for application in nonvolatile memory using the switchable dielectric polarization of ferroelectric material. To characterize such ferroelectric materials, a high-resolution tool is required for observing the microscopic distribution of remanent (or spontaneous) polarization of ferroelectric materials. 

Piezoresponse Characterization and domain engineering of ferroelectric materials... 

The driving force behind the rapid development of powder diffraction methods over the past 10 years is the increasing need for structural characterization of materials that are only available as powders. Examples are zeolite catalysts, magnets, metal hydrides, ceramics, battery and fuel cell electrodes, piezo- and ferroelectrics, and more recently pharmaceuticals and organic and molecular materials as well as biominerals. The emergence of nanoscience as an interdisciplinary research area will further increase the need for powder diffraction, pair-distribution function (PDF) analysis of powder diffraction pattern allows the refinement of structural models regardless of the crystalline quality of the sample and is therefore a very powerful structural characterization tool for nanomaterials and disordered complex materials. 

A. I. Kingon, Studies in the Preparation and Characterization of Selected Ferroelectric Materials, Ph.D. thesis. University of South Africa, 1981. 

Amorphous LiNbOs films made by sol-gel processing were subjected to a series of characterizations [57]. It was found that an amorphous LiNbOs film obtained by heating the gel film at 100°C for 2 h showed P-E hysteresis with remnant polarization Pr = 10 pC/cm2 and coercive field Ec= 110 kV/cm. Electron diffraction of such film showed a diffuse ring pattern characteristic of an amorphous nature. These are shown in Fig. 6 in which the scale for E is 147 kV/cm division and that for P is 5.6 pC/cm2 division. Further measurement showed a pyroelectric coefficient of 8 pC/cm2 K at 28°C. Note that for singlecrystal LiNbOa, Pr = 50 pC/cm2 and the pyroelectric coefficient was reported to be 20 pC/cm2 K [1]. Further, a piezoelectric resonance was observed at similar frequency range for both amorphous and crystalline LiNbOa, characteristic of a ferroelectric material [57]. 

Ferroelectricity is caused by a cooperative interaction of molecules or ions in condensed matter. The transition to ferroelectricity is characterized by a phase transition. Depending on the mechanism of how the molecules or ions interact in the material, we can classify the ferroelectric phase transitions and also the ferroelectric materials themselves into three categories (I) order-disorder type, (II) displacive type, and (III) indirect type. In the order-disorder type (I), the spontaneous... 

J. T. Dawley, G. Teowee, B. J. J. Zelinski, and D. R. Uhlmann, Piezoelectric Characterization of Bulk and Thin Film Ferroelectric Materials Using Fiber Optics, MTI Instruments Inc., Application Note. 

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