Phase states of nanocrystalline ferroelectric ceramics and their dielectric properties

Abstract

Using a nonlinear thermodynamic theory, we describe equilibrium polarization states and the macroscopic dielectric response of nanocrystalline ferroelectric ceramics with single-domain grains. The elastic clamping of individual crystallites by the surrounding material is explicitly taken into account via the introduction of a specific thermodynamic potential. Aggregate material properties are calculated with the aid of an iterative procedure based on the method of effective medium. The numerical calculations, performed for unpolarized BaTiO3 and Pb(Zr1−xTix)O3 ceramics, demonstrate that the equilibrium phase states of nanocrystalline ceramics may differ drastically from those of single crystals and coarse-grained materials. Remarkably, the theory predicts the coexistence of rhombohedral and tetragonal crystallites in nanocrystalline Pb(Zr1−xTix)O3 ceramics in a wide range of compositions and temperatures. For BaTiO3 ceramics, a mixture of rhombohedral and orthorhombic crystallites is found to be the energetically most favorable state at room temperature. The calculations also show that the dielectric properties of nanocrystalline ferroelectric ceramics may be very different from those of conventional materials due to the elastic clamping of single-domain crystallites.

Intrinsic versus extrinsic effects of the grain boundary on the properties of ferroelectric nanoceramics

“…It is noted that the value of the dielectric coefficient quickly drops as the grain size decreases. This result is consistent in trend with most experimental observations on unpoled nanoceramics [6,15,53].…”

“…Frey et al [15] and Buscaglia et al [16] showed that the distinct local property of the grain boundaries plays an important role in the size dependence. Frey and Payne [4] and Huan et al [5] examined the variation in the density of non-180° domain wall upon the reduction of grain size and correlated it to the intensified elastic constraint that could affect the overall properties [6,17]. More recently Ghosh et al [8] investigated the 90° domain wall dynamics in submicron-grained barium titanate (BaTiO 3 ) ceramics and discovered that the grain-size dependent property is mainly attributed to the variation in the domain wall mobility.…”

“…In addition to the complex microstructures inherited from their coarse-grained counterpart, ferroelectric nanoceramics possess some very unique features: the grain boundary area to volume ratio is much higher [2]; the non-180° domain twinning was reported being less popular [3,4]; the monodomain structure is relatively easy to form [5]; and the elastic clamping in the grains is believed to be more severe [4,6]. As a consequence, there are quite a few challenging problems in the study of ferroelectric nanoceramics.…”

Phase Diagram ofPb(Zr,Ti)O3Solid Solutions from First Principles

“…It may also take its origin from the presence of small grains in the grown ceramic, since Ref. [25] predicts that the coexistence of different phases may be energetically favorable (over a single phase) in a ceramic of fixed composition when the grain size is small. We also hope that our other predictions, including the ones about multiphase points, will be experimentally confirmed soon.…”

Influence of internal electric and elastic fields on characteristics of heterogeneous ferroelectric materials

“…[5][6][7][8][9][10][11][12] This dependence demonstrates an increase [13][14][15][16] as well as a decrease 17,18 of dielectric constant with decreasing the grain size.…”