Nanocrystalline BaTiO3 has been synthesized for the first time by a gas-condensation process using an electron beam evaporation system. BaTiO3 and Ti sources are vaporized simultaneously in either a mixed helium-oxygen or pure helium environment. Nano-BaTiO3 particles have an average particle size of approximately 18 nm. The processing parameters of the evaporation process are reported.

Nanocrystalline BaTiO3 has been prepared by a gas-condensation process. BaTiO3 and Ti sources are vaporized simultaneously in either a helium or an oxygen environment using an electron beam evaporation system. The stoichiometry of nanocrystalline BaTiO3 powders can be controlled precisely and reproducibly. Nanocrystalline BaTiO3 powders, with an average particle size of less than 20 nm, can be obtained by postannealing the as-evaporated powders at a temperature of 700 °C. These powders show good sintering behavior with a high density at a sintering temperature as low as 1250 °C. Differential thermal analysis indicated that nanocrystalline BaTiO3was formed through the reaction of Ba/Ti oxidized clusters. Dielectric properties of ceramics from nanocrystalline BaTiO3 are also reported.

The diffuse phase transition in ferroelectrics with mesoscopic heterogeneity has been discussed within the context of a superparaelectric model by using the Ginzburg-Landau formalism. In the Curie region ferroelectries with mesoscopic heterogeneity are treated as ''superparaelectrics'' consisting of a mass of polar clusters, each of which has Ising character. Based on the mean-field theory, the influence of the finite-size effects of polar clusters on their structural instability has been discussed by considering a coherent lattice coupling between two structurally different regions. In particular, we have analytically derived the explicit solutions of the distribution of local polarizations. In turn, the processes of polar nanophase precipitation and coarsening have been also discussed in conjunction with the local chemical or structural inhomogeneity. Moreover, we have also analyzed the relationship between the local polarization distribution and the static dielectric susceptibility in ferroelectrics with the nanometric scale heterogeneity. The width of the Curie region is dependent upon the distribution of the sum of localized correlation length, which reflects the size distribution of heterogeneity. The presented analysis reveals that the diffuse phase transition is closely associated with the existence of nanometric polar clusters and their physical size distribution. Intriguingly, our theoretical results bear a very close resemblance to most experimental observations.

Ferroelectric heterostructures of Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si and Au/Pb(Zr0.52Ti0.48)O3/Si have been fabricated by using laser ablation technique. Electrical properties of these ferroelectric field-effect transistors have been characterized through both the current vs voltage and capacitance vs voltage (C–V) measurements. The C–V characteristics of Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si heterostructures demonstrate a polarization switching behavior, showing a memory window as much as 1 V at 1 kHz. In addition, the experimental results reveal that a SiO2 buffer layer is essential for memory properties in the Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si gate structure.

The dielectric response of a ferroelectric multilayer, having a designed heterogeneity, has been studied near its phase transition range by use of the Landau-Ginzburg theory. The coherent lattice coupling between ultrathin layers can be significantly strong, resulting in a broad phase transition of the superlattice system as a whole. The thickness of layers and their spatial distribution hold the keys for enhancing dielectric properties in a broad temperature range.

Nanocrystalline BaTiO3 can be prepared by the gas condensation method at a temperature as low as 700°C, with an average particle size as small as 18nm. The stoichiometry of nanocrystalline BaTiO3 particles can be controlled precisely and reproducibly. Nanocrystalline BaTiO3 powders, fabricated by a novel e-beam evaporation method, show good sintering behavior with a high density at a temperature as low as 1200°C. These samples exhibit a relatively larger dielectric constant than that of coarse-grained BaTiO3. In addition, a thermal analysis has been also carried out to determinethe lowest temperature for forming nanostructured BaTiO3 from Ba/Ti oxidized clusters at ambient pressure.

The finite size effect in ferroelectrics results in structural instability, imposing a limitation of physical sizes and dimensions of materials in which electric dipoles can be sustained. To evaluate the ultimate limitation of physical sizes for a stable polar phase, the characteristic sizes, i.e., anisotropic correlation lengths of electric dipoles, in a ferroelectric have been examined by considering the surface effect. The size dependence on the Curie temperature in particular is calculated with consideration of crystallographic anisotropy. The mean-field theory shows that the limitation of transverse critical sizes is strongly dependent upon the thickness. In turn, the limitation of the critical thickness is also closely associated with the transverse critical sizes.

The onset of long-range order in the size-driven ferroelectric phase transition has been discussed extensively by use of mean field theory in the literature. In order to prevent erroneous analysis of the dielectric permitivity of nanometric sized ferroelectrics, we present a pertinent description of the dielectric susceptibility of nanostructured ferroelectrics within the context of Landau-Ginzburg theory. Consequently, we also discuss the influence of size on the dielectric permittivity of thin films and relevant implications.