Sunao Sugihara

Processing of Porous 3-3 PZT Ceramics Using Capsule-Free O2-HIP

The processing of porous 3-3 type PZT ceramics was investigated using capsule-free O2-HIP. Porous PZT sintered bodies with relative density of about 50-80% were prepared from the green compacts with various amounts of spherical Polymethylmethacrylate (PMMA) particles. They exhibited a homogeneous microstructure with a bimodal distribution consisting of small pores of several µm and large pores of 50-80 µm in the PZT matrix. Little densification of porous PZT sintered bodies occurred after capsule-free O2-HIP treatment, and the neck growth of PZT interparticles was well developed, leading to the formation of porous 3-3 type PZT ceramics with a higher connectivity. The HIPed porous ceramics possessed a large permittivity and a small depolarizing factor of about half those of normally sintered porous PZT bodies.

Thermoelectric properties of magnesium silicide processed by powdered elements plasma activated sintering method

Efficient, inexpensive and non-toxic thermoelectric elements such as silicides should be developed for large scale application such as recovering the combustion heat of municipal solid waste, of which the characteristics are greatly fitted to thermoelectric power generation. This paper introduces the characterization and thermoelectric properties of undoped and doped n-type magnesium silicide processed by the powdered elements spark plasma sintering method. The patterns by powder X-ray diffractometry showed that it had typical polycrystalline phase. The temperature dependence of thermoelectric properties such as the Seebeck coefficient and electrical conductivity were measured for the temperature range from 300 K to 773 K. As a result, a power factor value 6.0/spl times/10/sup -4/ (W/mK/sup 2/) was obtained at 773 K for a doped sample.

Sintering of Piezoelectric Ceramics with CO2 Laser

Sintering of Pb(Zr 0.53 Ti 0.47 )O 3 with a CO 2 laser is discussed to indicate the possibility of a new method of synthesizing piezoelectric ceramics. Thestarting materials are (1) PbO, ZrO 2 and TiO 2 , and (2) Pb 3 O 4 , ZrO 2 and TiO 2 . The green oxide pellets are irradiated with a CO 2 laser at various powers of 143, 286 and 1857 W/cm 2 in a flow rate of 350 cm 3 /min of O 2 /Ar(10 5 Pa). In both cases, the formations of Pb(Zr, Ti)O 3 were recognized by XRD (X-ray diffraction) analysis although some starting materials remained at the lower power. The microstructures are also discussed

Electronic Structures and Dielectric Properties of Substituted BaTiO3

Electronic structures were investigated on BaTiO3 substituted with other elements, such as Ca, Sr, Sc, Y, Ce and Gd for Ba, using a molecular orbital treatment that yielded net charge, bond order, density of states, energy levels and contour maps of electron density. By this method, the transformation into paraelectric material by ferroelectric material was discussed with respect to relative permittivity as measured experimentally. Furthermore, X-ray photoelectron spectroscopy (XPS) at the valence energy level was used on the Sr-substituted cluster, and the experimental spectrum was compared to the calculated one to evaluate the appropriateness of the cluster model. The overlap population between the A site in BaTiO3 and oxygen showed either a covalent or ionic nature depending on the elements. In addition, the relative permittivity related to the overlap population between site A and Ti resulting in lower permittivity for the trivalent elements such as Y and Gd. The computer simulation can be applied to design properties of the ceramics in the microwave range.

Wetting of silicon single crystal by silver and tin, and their interfaces

A study of wetting of silicon single crystals and electrode metals was undertaken to investigate the wetting mechanisms and to clarify the interfaces between the silicon wafer and silver and tin. The experiments were performed using a high-temperature surface tension measuring equipment in vacuum and 5% H2/Ar atmospheres (105 Pa). The contact angles were measured by taking photographs through a telescope during the wetting experiment. Silicon was wetted by silver with a contact angle of 42°, whereas it was not wetted by tin in vacuum and in the 5% H2/Ar atmosphere. However, heat treatment of silicon in vacuum or 5% H2/Ar atmosphere prior to the wetting experiment reduced the contact angles compared to the cases with no heat treatment. The bonding interfaces between silicon and silver are also discussed.

Thermoelectric properties of sintered magnesium compounds

The thermoelectric properties of the sintered magnesium compounds such as magnesium silicide and magnesium stannide have been researched in order to apply to a thermoelectric power generation system using combustion heat of municipal solid waste. Temperature dependencies of thermoelectric properties such as Seebeck coefficient, electrical resistivity and thermoelectric power factor are measured for the temperature range from 300 K to 770 K. The non-dimensional figure-of-merit for the sintered magnesium silicide is obtained about 0.4 at 600 K in the initial stage. The durability of magnesium compound elements is also discussed.

Preparation of porous PZT with high connectivity using capsule-free O2-HIP and their dielectric properties

Abstract The processing of porous PZT ceramics with high connectivity was investigated using capsule-free O2-HIP technology. PreHIPed porous PZT bodies were prepared by pressureless-sintering of green compacts with various amounts of spherical PMMA particles, followed by hot-isostatically pressed at 1100°C and 200 MPa for 1 h in 5% O2/Ar mixture gas atmosphere. Little densification of porous PZT sintered bodies occurred by capsule-free O2-HIP treatment, resulting in the formation of well-developed neck growth between PZT grains. They exhibited a homogeneous microstructure with a bimodal pore distribution consisting of both several μm and 50 ∼ 80 μm pore sizes. The HIPed porous PZT ceramics have a larger permittivity and a smaller depolarizing factor about a half rather than those of pressureless-sintered porous PZT bodies, suggesting that the HIPed PZT has a higher connectivity. Piezoelectric g33 constant-porosity relations were also described.

Dielectric Property Change of Ferroelectrics and Electronic Structures

Electronic structures were investigated in relation to the relative permittivity of ferroelectrics such as the ABO3-type and A- and/or B-substituted materials, using a molecular orbital method. The A-site ions were Ba, Pb, Sr and Ca, and the B-site ion was Zr. Calculation was performed using the DV-Xα (discrete variational Xα) method and the overlap population, which is related to the covalent bonding nature, was discussed together with the effective charge. As a result, the change from ferroelectric to paraelectric was found to be associated with the covalency between the A-site ion and Ti or Zr. Furthermore, the energy for π-bonding between O2p and Ti3d (or Zr4d in AZrO3) shifted toward the lower energy level by substitution of the A site with Ca to give a lower relative permittivity. Then, we studied the effect of quantitative changes of the amount (x = 0.25, 0.5, 0.75) of A-site ions in the (Ba1-x, Srx)TiO3 system on the electronic structures, and suggested that the bonding nature between O and Ti is related to the relative permittivity of the system.

Doping effect of metal into iron disilicide on electronic structures and thermoelectric properties

Doping effects of elements into FeSi/sub 2/ on the electronic structures were studied relating to the thermoelectric properties. The studied elements were the metals possessing d- or f-electrons such as Mn, Co, Zn and Hf, W, os (f/sup 14/ series) and Nd, Eu and Yb in the lanthanide series, although only Yb, Hf and Os are reported here. The calculation was performed using the discrete variational X/spl alpha/ molecular orbital method. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) relates to electrical conductivity, and the Seebeck coefficient associated with the gap between HOMO and LUMO levels possessing the same symmetry which were degenerate. In experiment, doping with Yb/sub 2/O/sub 3/ increased the Seebeck coefficient and electrical resistivity did not change much, resulting in an improvement as large as twice the figure of merit for thermoelectricity.

Hetero interfaces of Bi-based superconductor/insulator and electrical properties

A thick film of the Bi-based superconductor was fabricated onto the oxide polycrystalline substrates such as MgO, ZrO 2 and SrTiO 3 where system will be a new composite. The thickness was about 10 μm. The lowest electrical resistivity of 11 mΩ cm at 110 K for the isostatic pressed system of the superconductor/MgO, and 10 mΩ cm at 110 K for the SrTiO 3 substrate. The large grain size at the surfaces was found to be important as well as the dense surfaces. No changes of the critical temperature were found on any substrate. The interfaces between the film and the substrate can be controlled by the pressing process which is important to reduce the electrical resistivity.