BaTiO3 Nanostructures Research Articles

Macroscopic ferroelectricity and piezoelectricity in nanostructured BiScO3–PbTiO3 ceramics

We have studied the macroscopic electrical properties of highly dense, nanostructured ceramics of BiScO3–PbTiO3 with high Curie temperature and piezoelectric activity. Materials were processed by spark plasma sintering of nanocrystalline powder obtained by mechanosynthesis. Results indicate that the nanostructured material still presents the ferroelectric transition above 700K. Ferroelectric switching is unambiguously demonstrated. Furthermore, ceramic disks were poled and their radial piezoelectric resonance was excited, which has not been achieved in nanostructured BaTiO3 ceramics.

Growth Mechanism of Shape-Controlled Barium Titanate Nanostructures through Soft Chemical Reaction

Morphology-controlled barium titanate (BaTiO3) nanostructures, from single-crystal nanorods to nanoparticles, were synthesized by tuning the reaction time of a soft chemical process. Based on the morphology change of the nanostructures, the growth mechanism of the shape-controlled BaTiO3 nanostructures by the soft chemical reaction method was suggested. With the reaction time of 42 h, single-crystal BaTiO3 nanorods with flat surface of facets and defined crystal axis were obtained. As the reaction time was extended to 50 h, a certain volume of nanorods converted to nanoparticles generated by a redissolution−growth reaction. When the reaction time was further elongated to 72 h, the volume of nanoparticles in the product notably increased with single grains of particles that have diameters up to ∼200 nm. It was determined that an ion exchange and the structural transformation from the layer structure of the precursor into the perovskite structure prevailed at an early stage of the soft chemical reaction, and then the nanorods changed to nanoparticles due to the redissolution−growth reaction for reaction times over 42 h.

Shape-Controlled Monocrystalline Ferroelectric Barium Titanate Nanostructures: From Nanotubes and Nanowires to Ordered Nanostructures

We report for the first time on the controlled hydrothermal synthesis of barium titanate nanostructures using Na2Ti3O7 nanotubes and nanowires as synthetic precursors. A variety of nanostructured BaTiO3 have been prepared, exhibiting either simple shapes of nanowires, nanosheets, nanocubes, and hexagonal nanoparticles or ordered architectures of coral-like nanostructures of assembled nanorods, starfish-like nanostructures, and sword-like nanostructures. The shapes of the various BaTiO3 products are found to be dependent on the concentration of Ba(OH)2, the temperature, and the nature of the precursors. The synthesis route exploits the differences in the hydrothermal stability of the Na2Ti3O7 nanotubes and nanowires and the temperature-dependent crystal structure of barium titanate. Various nanoblocks, including nanosheets and nanorods formed from the Na2Ti3O7 nanotubes and nanowires, respectively, grow and assemble to form the ordered BaTiO3 nanostructures. This represents a new approach that is capable of assembling ordered perovskite nanostructures using relatively large nanoblocks formed from layered alkali-metal titanates. The process offers more flexibility than those using inorganic titanium salts or organometallic titanium compounds, which commonly leads to the formation of only BaTiO3 nanoparticles.

Coupling interaction in multiferroic BaTiO3–CoFe2O4 nanostructures

Recent experimental results (Zheng et al 2004 Science 303 661) have shown that a 1-3-type BaTiO3–CoFe2O4 composite film exhibited a strong coupling between the ferroelectric and ferromagnetic order parameters. The coupling interaction in the nanostructured multiferroic film could be different from that in a bulk composite because there exists a giant residual stress/strain in the film. In this paper, by considering the influence of the three-dimensional residual strain in the film, the magnetically induced polarization of the nanostructured BaTiO3–CoFe2O4 multiferroic films has been studied using the Landau–Ginsberg–Devonshire thermodynamic theory. The calculation results show that the 1-3-type nanostructured composite film could produce a ferroelectric–ferromagnetic coupling larger than that of its bulk counterpart which is in broad agreement with the experimental results. The 2-2-type nanostructured composite films were found to produce much less coupling interaction in comparison with the 1-3-type film. The dependence of multiferroic coupling on composition and temperature was analysed on the basis of the calculated results.

Well-ordered arrays of pyramid-shaped ferroelectric BaTiO3 nanostructures

Monolayers of monodisperse latex spheres of micron size were used as deposition masks to fabricate arrays of ferroelectric nanostructures by pulsed laser deposition using a BaTiO3 target. First, arrays of well-ordered structures were prepared on SrTiO3:Nb (100) single-crystal substrates at room temperature. Investigations of these isolated as-deposited nanostructures by atomic force microscopy revealed that they have a pyramid-like shape with about 200 nm lateral size at half their height and form a regular hexagonal pattern. Then postdeposition annealing was used to crystallize the nanostructures. The ferroelectric properties of the crystalline structures were investigated by scanning force microscopy in piezoresponse mode. Piezoelectric hysteresis loops were recorded, demonstrating that the barium titanate nanopyramids have a remanent polarization and are switchable by an electric field, i.e., they are indeed ferroelectric.

Patterning and switching of nano-size ferroelectric memory cells

A “top-down” approach using e-beam lithography and a “bottom-up” one using self-assembly methods were used to fabricate ferroelelectric Pb(Zr,Ti)O3, SrBi2Ta2O9 and BaTiO3 nanostructures with lateral sizes in the range of 30 nm to 100 nm. Switching of single sub-100 nm cells was achieved and piezoelectric hysteresis loops were recorded using a scanning force microscope working in piezoresponse mode. The piezoelectricity and its hysteresis acquired for 100 nm PZT cells demonstrate that a further decrease in lateral size under 100 nm appears to be possible and that the size effects are not fundamentally limiting on increase density of non-volatile ferroelectric memories in the Gbit range.

Nanocrystalline BaTiO3 from the Gas-Condensation Process

ABSTRACTNanocrystalline 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.