Takeshi Ukai

Preparation and Electrical Properties of Carbon Nanotubes Dispersed Zirconia Nanocomposites

Multi Wall Carbon Nanotubes (MWCNTs) with a diameter of 20-30 nm were used as a conductive phase to add electric conductivity to yttria stabilized tetragonal zirconia (3Y-TZP). Almost fully dense 3Y-TZP/MWCNTs nanocomposite was obtained by pressureless sintering under inert atmosphere and Hot Isostatic Pressing (HIP) treatment. The conductivity of the nanocomposites increased with increasing content of MWCNTs. Moreover, the fracture toughness increment of the composite was confirmed at 0.5 wt% addition. Scanning electron microscopy and transmission electron microscopy observation of the microstructures showed that MWCNTs were fairly homogeneously dispersed in the 3Y-TZP matrix.

A CAS-DFT study of fundamental degenerate and nearly degenerate systems

We present simple CAS-DFT approaches for degenerate and nearly degenerate systems. In this method, we do not employ any auxiliary variables, but employ the effective CASCI-DFT and CASSCF-DFT equations for the ground and excited states. Simple applications for fundamental systems such as atomic multiplet states (C, N+n , and O+n ), the transition metal complex V(III)L6 (L = H2O and CO) and the Cu(II) acetate dimer Cu(II)2(Ac)4(H2O)2 are presented. The results are discussed from the viewpoint of the shapes of the potential curves of several nearly degenerate spin states, the theory of molecular magnetism and the reliability of the CAS space employed. The computational results are fully compatible with the experimental results available, and also with those of ligand field theory.

Multireference Density Functional Study of Atomic and Molecular Magnetic Systems

We present the complete‐active‐space density functional theory (CAS‐DFT) approach for degenerate and nearly degenerate systems. In this method, we solve the effective CAS‐DFT equation in order that the Euler equation of CAS‐DFT is satisfied. The simple applications for atomic and molecular magnetic systems such as atomic multiplets, organic radicals, and Cu(II) acetate are presented. The results are discussed in relation to the theory of magnetism.

Percolation Analysis of Electrical Conductivity and Mechanical Properties for CNT-Dispersed Y-TZP Nanocomposites

Multi-wall carbon nanotubes (MWCNTs) with a diameter of 20-30 nm were dispersed as a conductive phase into yttria stabilized tetragonal zirconia polycrystalline (3Y-TZP) to add electrical conductivity. The 3Y-TZP/MWCNT nanocomposites were fabricated by pressureless sintering under inert atmosphere. Electrical conductive function was successfully introduced by small amount of CNT addition. Critical volume fraction of the conductive phase for the percolation was analyzed and was found to be 0.390 vol% of CNT, which was much smaller than that for nano-sized carbon black dispersed 3Y-TZP (2.55 vol%). Microstructural investigation revealed that dispersed CNTs formed continuous 3-dimensional nano-network within the 3Y-TZP matrix, that contributed to the excellent conductive properties. Fracture strength was not improved much, while fracture toughness was increased by the CNT addition, due mainly to its crack bridging and/or pull-out mechanisms. It was considered that the use of anisotropic nano-sized conductive phase is advantageous to obtain electrically functionalized nanocomposite ceramics.