Volume 86, Issue 10, 15 November 1999
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
86(1999); http://dx.doi.org/10.1063/1.371586View Description Hide Description
Domain structures arising as a result of pulsed electric fields are investigated in (PZN-PT) 〈001〉 single crystals by means of etching and environmental scanning electron microscope. It is shown that randomly orientated dendritic domain patterns were created under a pulsed electric field condition. The dendritic patterns are believed to be the result of local electric field and elastic deformation. Dendritic structures are also found during a back-switching process in 0.92PZN-0.08PT  single crystals. It is hypothesized that these unusual nonequilibrium domain structures are the result of local defects and space charge in the relaxor PZN-PT crystals.
86(1999); http://dx.doi.org/10.1063/1.371587View Description Hide Description
Using a two-dimensional Ginzburg–Landau model and the finite-elementcomputational method, we have calculated stable domain configurations resulting from a second-order ferroelectric phase transition for a finite-sized system. The boundary conditions applied here correspond to fully charge compensated situations, either by surfaceelectrodes or by the injection of charges (or defects) near the sample surface. The domain wall thickness of a finite system without surfaceelectrodes was found to become thinner as it approaches sample surfaces. This is distinctively different from that of an infinite system for which a planar wall assumption can be used. The orientation of the macroscopic polarization of a finite system without surfaceelectrodes was found to be determined by its aspect ratio. A size effect was observed when all the dimensions were reduced simultaneously. The relaxation process in the formation of domains and the switching process have also been simulated for charge neutral boundary conditions using a time dependent Ginzburg–Landau model. The simulation results verified that the surfaces are the favored nucleation sites for domain switching.
Effects of fluorine–oxygen substitution on the dielectric and electromechanical properties of lead zirconate titanate ceramics86(1999); http://dx.doi.org/10.1063/1.371588View Description Hide Description
In this study, a fluorine–oxygen substitution in lead zirconate titanate(PZT)ceramics with a nominal composition of (PZT)doped with 1% MgO is proposed. The evolution of four dielectric and electromechanical coefficients— and —with increasing fluorine concentration showed that (MgO and F)-doped PZTceramics are harder than only MgO-doped PZT (0 at. % F). The influence of the F–O substitution on the temperature dependence of the frequency constant and the stress dependence of the piezoelectric coefficient was investigated. A hysteretic free response of and the lowest stress dependence of were obtained for the (MgO and 4 at. % F)-doped PZT specimen. This material also exhibits the highest in the (MgO and F)-doped PZT family and seems to be stoichiometric and without oxygen vacancies. For comparison, both the temperature and stress dependences of two commercial PZTceramics are shown. The study of the influence of the Zr/Ti ratio on the temperature dependence of revealed that fluorine stabilizes the rhombohedral phase/tetragonal phase interface. Both types of stability, versus temperature and uniaxial mechanical stress, may be linked to the domain wall configuration stabilization by dipoles which are less mobile than ones.
86(1999); http://dx.doi.org/10.1063/1.371589View Description Hide Description
The piezoelectric responses of different piezocrystals, rigidly backed, have been studied under constant and impulsive stress. Equations connecting electrical and mechanical interactions have been coupled to find the response. The rates of growth and decay of piezovoltage have been found to vary widely from material to material.
86(1999); http://dx.doi.org/10.1063/1.371590View Description Hide Description
Computer calculations of the formation of a percolation path across a finite lattice are used to modeldielectric breakdown. The classical scaling relations for percolation are expected to be valid only for large (finite) systems near We investigate the opposite limit of very small samples, comparable to the lattice spacing. It is shown that relatively simple numerical calculations can quantitatively describe the statistics and thickness dependence of oxide breakdown in thin samples. The critical defect density for breakdown shows a strong decrease with thickness below about 5 nm, then becomes constant below 3 nm. Both of these features can be quantitatively explained by percolation on a finite lattice. The effective defect “size” of about 3 nm is obtained from the thickness dependence of the breakdown distributions. The model predicts a singular behavior when the oxide thickness becomes less than the defect size, because in this limit a single defect near the center of the oxide is sufficient to create a continuous path across the sample. It is found that a given percolation path has a probability of about for initiating destructive breakdown. We investigate both homogeneous percolation and percolation in a nonuniform density of sites.