Tomokazu Tanase

Size Effect on Crystal Structures of Barium Titanate Nanoparticles Prepared by a Sol-Gel Method

Barium titanate nanoparticles were synthesized by the hydrolysis of complex alkoxide precursor that was prepared in a reflux of metallic barium and tetraethylorthotitanate in solvent. The hydrolysis was performed by the addition of water/ethanol solution to the precursor solution. As reflux time increased, particle sizes, which were measured with transmittance electromicroscopy, became smaller followed by sharpening of size distribution. As water concentration and benzene content in the hydrolysis increased, the particle size increased with crystallite size that was determined with X-ray diffractometry. No significant difference was observed between the particle and crystallite sizes up to 30 nm. Over the size of 30 nm, the particle size was larger than the crystallite size because of generation of polycrystallites. Annealing treatments in air at 400 and 1000°C also increased both the particle and crystallite sizes. The crystallite sizes estimated from the (111) peaks were smaller than those from (110) peaks in a range of sizes larger than 40 nm, which indicated that the critical crystallite size of transformation from cubic to tetragonal structures was approximately 40 nm.

Low Temperature Processing of Crystalline Lead Zirconate Titanate (PZT) Film and the Direct Micropatterning by Laser-Induced Pyrolysis of a Sol-Gel-Derived Film

A novel low-temperature processing of crystalline lead zirconate titanate (PZT) film was developed. The beam from an Ar ion laser was focused and scanned on the sol-gel derived film, and it induced pyrolysis of the precursor film with spatially selectivity. Development of the film using an acidic solution gave the PZT micropattern. The Raman spectrum of the micropattern exhibited the characteristics of crystalline PZT.

Low-Temperature Synthesis and Dielectric Properties of Single-Phase Lead Zirconate Titanate Thin Film with a Nano Particle Seeding Technique

The low temperature synthetic method, which combines chemical solution deposition and nm-seeding technique, was applied to the fabrication of lead zirconate titanate (PZT) thin films. Nano-crystallines of barium strontium titanate (BST) particles were prepared by the hydrolysis reaction of the complex alkoxides. PZT precursor solutions containing the BST particles were spin-coated on Pt/Ti/SiO 2 /Si substrates to film thickness of 500 − 800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and crystallized PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10 -6 A/cm 2 at applied electric field from 0 to 64 kV/cm.

Micropatterning and crystallization of sol-gel-derived dielectric film by laser direct writing

Low temperature crystallization and the micropatterning of lead zirconate titanate (PZT) film were achieved by laser direct writing method using a sol-gel derived precursor film. After scanning of an Ar ion laser beam through an objective lens, the etching of the unirradiated area of the precursor film with an acidic solution gave micropatterns with a resolution of several ìm. The formation of crystalline micropatterns was confirmed by micro-Raman spectroscopy. The laser direct writing method provides a low-temperature processing of crystalline PZT film while the crystallization of PZT needs the heat treatment above 600 °C in the case of convenient methods. The influences of the power density of the laser beam were investigated. With increasing the laser power density, the change from tetragonal to rombohedral phase was observed. The micropattern with tetragonal phase showed residual carbon. The carbon contamination could be removed by heat treatment in air. The direct laser writing of crystalline barium titanate (BT) film was also successfully performed using sol-gel derived BT films containing BT nano-crystalline seeds. The dielectric constant of the crystalline BT micropatterns reached 76.2 at 100 kHz.