Polycrystalline Ferroelectric Materials Research Articles

Aggregate linear properties of ferroelectric ceramics and polycrystalline thin films: Calculation by the method of effective piezoelectric medium

The effective dielectric, piezoelectric, and elastic constants of polycrystalline ferroelectric materials are calculated from single-crystal data by an advanced method of effective medium, which takes into account the piezoelectric interactions between grains in full measure. For bulk BaTiO3 and PbTiO3 polarized ceramics, the dependences of material constants on the remanent polarization are reported. Dielectric and elastic constants are computed also for unpolarized c- and a-textured ferroelectric thin films deposited on cubic or amorphous substrates. It is found that the dielectric properties of BaTiO3 and PbTiO3 polycrystalline thin films strongly depend on the type of crystal texture. The influence of two-dimensional clamping by the substrate on the dielectric and piezoelectric responses of polarized films is described quantitatively and shown to be especially important for the piezoelectric charge coefficient of BaTiO3 films.

Intrinsic and Extrinsic Size Effects in Fine‐Grained Morphotropic‐Phase‐Boundary Lead Zirconate Titanate Ceramics

The processing, electromechanical properties, and microstructure of lead zirconate titanate (PZT) ceramics over the grain‐size range of 0.1‐10 μm were studied. Using measurements over a large temperature range (15‐600 K), the relative role of extrinsic contribution (i.e., domain‐wall motion) was deduced to be influenced strongly by the grain size, particularly for donor‐doped PZT. Analytical transmission electron microscopy studies were conducted to investigate the trend in domain configurations with the reduction of grain size. The correlations between domain density, domain variants, domain configurations (before and after poling), spontaneous deformation, and the elastodielectric properties were qualitatively discussed, leading to new insights into the intrinsic and extrinsic effects and relevant size effects in ferroelectric polycrystalline materials.

Electromechanical nonlinearity of ferroelectric ceramics and related non-180° domain wall motions

Abstract Using an optical interferometer and other experimental techniques, the mechanical and dielectric response of lead zirconate titanate Pb(ZrxTi1-x)O3 ceramics to an a.c. electric field have been investigated directly. The experimental results demonstrate the importance of the domain wall motion in generating the electromechanical nonlinearities in ferroelectric ceramics. It has been verified that the couplings between the acoustic vibrations and the movement of domain walls is an important factor in terms of extrinsic properties of ferroelectric polycrystalline materials. A phenomenological theory has been extended to describe the extrinsic contributions to the piezoelectric, elastic and dielectric properties. These effects can be attributed to both the linear and nonlinear vibrations of non-180° domain walls in ferroelectric ceramics. The proposed theory shows qualitative agreement with the experimental results.

One dimensional dynamic electromechanical constitutive relations of ferroelectric materials

We present a macroscopic theory for the dynamic response of a poled polycrystalline ferroelectric material describing its coupled electromechanical interactions. The treatment is restricted to an idealized material representing the simplest system capable of displaying ferroelectricity; it includes changes in both the magnitude of the electric dipoles and the orientation of the domains. Coupling between the electrical and mechanical properties of the material is considered and the constitutive equations are linearized to illustrate the resulting dynamic response.

Electron-Mirror-Microscope Analysis of Surface Potentials on Ferroelectrics

Electron-mirror photomicrographs were taken of barium titanate single-crystal and lead zirconate-titanate polycrystalline ferroelectric materials. Electrical potential distributions were observed with the microscope on the surfaces of both materials. The domain structure of barium titanate was evident as was the transition from the ferroelectric to the paraelectric state. Lead zirconate-titanate ceramic in the unpoled and poled states appeared significantly different as did regions polarized in opposite directions. These observations are explained in terms of bound surface charges.

Quality of a Ferroelectric Material

The paper describes a simple method of measuring the nonlinear properties of a ferroelectric material at microwave frequencies. A composition of commercial polycrystalline barium titanate, of stated Curie temperature of 20/spl deg/C, and of polythene powder was investigated. The incremental permittivity of the specimen at both increasing and decreasing biasing field was observed at X, C and S band. The effective dielectric constant of the specimen, for the same biasing field, was lower for increasing field, contrary to the theoretical analysis. Diamond's model of polycrystalline ferroelectric materials provides a qualitative explanation for the observed anomalous behavior of the specimens. An experimental arrangement for the observation of the microwave equivalent of a low-frequency ferroelectric loop is suggested.