Teruhisa Makino

Crystallinity of Barium Titanate Nanoparticles Synthesized by Sol-Gel Method

We synthesized barium titanate (BaTiO3) nanoparticles by sol-gel process and investigated their crystallization behavior using differential scanning calorimetry and X-ray diffraction. BaTiO3 nanoparticles with various degrees of crystallinity were obtained by adjusting synthesis conditions. Under aging conditions that do not allow dealcholization reaction to complete, many hydroxyl ligands remain in as-synthesized BaTiO3 nanoparticles, resulting in the formation of voids or defects in the nanoparticles after calcination. It is essential to use high concentration alkoxides precursor solutions for producing BaTiO3 nanoparticles with high crystallinity at low temperature.

High-performance dielectric thin film nanocomposites of barium titanate and cyanoethyl pullulan: controlling the barium titanate nanoparticle size using a sol–gel method

A monodispersed BaTiO3 nanoparticle sol was prepared by a sol–gel method, and the sizes of the obtained nanoparticles were successfully controlled from 15 to 60 nm by controlling the amount of H2O introduced for the hydrolysis reaction. Cyanoethyl pullulan (CEP) was added to the BaTiO3 sol to prepare a nanocomposite ink of BaTiO3 and CEP. A thin film was fabricated by spin-coating the ink on a Pt/Ti/SiO2/Si wafer. The device obtained from the 30 nm BaTiO3/CEP nanocomposite ink demonstrated the highest dielectric constant, about 50 at 1 kHz, during the particle size range from 15 to 60 nm. The temperature dependence of the dielectric constant at approximately 120 °C is eliminated using our BaTiO3 nanoparticles, because of their cubic crystal structure, which does not show a transformation at 120 °C. These improvements of the dielectric properties are important for the development of thin film-type capacitors for compact electric devices.

Sedimentation of Barium Titanate Nanoparticles in a Suspension under Application of an Electric Field

Barium titanate nanoparticle (BT-NP) suspensions were prepared by dispersing sol-gel-derived BT-NPs in ethylene glycol monomethyl ether (EGMME) under sonication. When an electric field was applied, a part of the BT-NPs in a suspension was deposited on the cathode by electrophoretically deposition and most of the rest of the BT-NPs settled down towards the bottom of a container. The concentration of BT-NPs in the lower part of the container (Cbottom) increased with time until the Cbottom reached a specific concentration (threshold concentration) at which sedimentation of BT-NPs start to occur. The threshold concentration of the nanoparticles sedimentation gave a significant influence upon the aspect of a BT-NPs deposit formed on the cathode.

Preparation of Barium Titanate Nanoparticle Thin Films by the Electrophoretic Deposition Method Using Polyacrylic Acid as a Charge-Compensating Agent

Using the electrophoretic deposition (EPD) method, we prepared barium titanate nanoparticle (BT-NP) thin films by depositing BT-NP monodispersed in ethylene glycol monomethyl ether (EGMME) onto an electrically conductive substrate coated with polyacrylic acid (PAA). Deposition efficiency was increased compared to conventional EPD, and the uniformity of the film thickness was also improved as a result of the BT-NPs cohesion effect of the PAA coating on the substrate in addition to the electrophoretic deposition effect of the electric field. When low-molecular-weight PAA was used, the film was reinforced since PAA, which coats the substrate, diffused close to the surface of the BT-NP film during film formation. A crack-free BT-NP film was produced with a film thickness of several micrometers.

Effect of the Nano-Sized BaTiO3 Gel Particles on Dielectric Properties of Thin Films

We synthesized nanocrystalline BaTiO3 particles by sol-gel process and made evaluations concerning their size and crystallinity with TEM, XRD and small angle X-ray scattering (SAXS). The BaTiO3 particles were found to be composed of well-crystallized particles with sizes greater than 5nm and poorly-crystallized (almost amorphous) particles smaller than 3nm. We obtained BaTiO3 ceramic thin films of around 500nm in thickness by spin coating using a suspension of the nanocrystalline particles, followed by firing at 800°C. The quality of BaTiO3 films prepared was strongly dependent on the volume ratio of well-crystallized particles in the suspension. The film which obtained the highest quality, exhibited a capacitance of 530nF/cm (at 1 kHz).