Weon-Pil Tai

Humidity sensitive properties of nanostructured Al-doped ZnO:TiO2 thin films

Nanostructured Al-doped ZnO(AZ):TiO2 films are prepared using a sol–gel process and the humidity sensitive properties of the films are investigated. The films possess nanostructure. Nanostructured-bilayered TiO 2/AZ film exhibits improved linearity with narrow hysteresis loop in the resistance variation for relative humidity than single layered film. The resistance of the bilayered TiO 2/AZ film changes by nearly three orders of magnitude during the relative humidity variation of 30–90%. The humidity sensitive properties in the nanostructured AZ:TiO2 films are discussed.

Humidity sensing behaviors of nanocrystalline Al-doped ZnO thin films prepared by sol–gel process

Nanocrystalline Al-doped ZnO(AZO) thin films prepared by sol–gel method were used for studying the variation of resistance with humidity. The particle size of the films exhibits nanometer order with zincite structure and the thickness of the films increases linearly with the number of coatings. The AZO film coated five times and annealed at 500 °C exhibits the highest sensitivity for the humidity, which shows three order change in the resistance during the relative humidity variation from 20 to 90%. It is considered that the high humidity sensitivity is due to proton hopping between water molecules adsorbed on the film surfaces with capillary nanopores.

Eosin Y-sensitized nanostructured SnO2/TiO2 solar cells

Abstract The photoelectrochemical behaviors of eosin Y (organic dye)-sensitized nanostructured SnO2/TiO2 coupled and SnO2+TiO2 composite solar cells were studied. The value of incident photon-to-current conversion efficiency (IPCE) in the coupled system was higher than the composite system. A maximum IPCE value, 63%, was reached at 525 nm wavelength in the coupled cell with 3.5-μm-thick SnO2 and 7-μm-thick TiO2. The IPCE difference in the coupled and composite cells sensitized by eosin Y dye is discussed.

Preparation and humidity sensing behaviors of nanocrystalline SnO2/TiO2 bilayered films

Abstract The single- and bi-layered nanocrystalline SnO 2 /TiO 2 films are prepared using a sol–gel process and the humidity sensing behaviors of the films are investigated. The films possess the grain size of nanometer order and nanoporous structure. The bilayered films exhibit a better linearity with narrower hysteresis loop in the resistance variation for relative humidity than single layered films. The bilayered SnO 2 /TiO 2 film shows high sensitivity with nearly three orders change in the resistance during the relative humidity variation from 30 to 90%. The humidity sensing behaviors in the single- and bi-layered films are discussed.

A new approach to anorthite porcelain bodies using nonplastic raw materials

Abstract New anorthite porcelain bodies using only nonplastic raw materials, such as feldspar, quartz, and aluminous cement, without using a binder were fabricated, and their properties were investigated. The green strength was relatively high due to hardening by the hydration reaction of the aluminous cement with the feldspar in a moist atmosphere. The phases found in the green body were feldspar, CaAl 2 O 4 , CaAl 4 O 7 , α-quartz and a small amount of CaAl 2 Si 2 O 8 ·4H 2 O. The phases in the fired body were α-quartz, anorthite, glass and a small amount of α-Al 2 O 3 ; cristobalite formed only at a quartz content of 60 wt.%. Higher flexural strength at a composition containing 30 wt.% feldspar is attributed both to fewer crack origins as a result of appropriate vitrification and to greater residual stress caused by the larger difference in the thermal expansion coefficient between the glass matrix and the quartz and anorthite grains.

Photoelectrochemical properties of SnO2/TiO2 coupled electrode sensitized by a mercurochrome dye

Abstract The photoelectrochemical properties of the mercurochrome-sensitized SnO 2 /TiO 2 coupled cell were studied with TiO 2 film thickness at a constant SnO 2 thickness. The optimal film thickness in the coupled cell is 3.5-μm-thick SnO 2 and 6–7-μm-thick TiO 2 and the maximum incident photon-to-current conversion efficiency (IPCE) value reached about 30.5% at 520 nm. The higher IPCE value in the 3.5 μm SnO 2 /6–7 μm TiO 2 coupled cell is attributed to a better charge separation by fast electron transfer process from excited dye to TiO 2 to SnO 2 .

Preparation and humidity-sensing properties of nanostructured potassium tantalate thin films

Nanostructured potassium tantalate (KT) thin films are prepared using a sol–gel process and the humidity-sensing behaviors of the films are investigated. The films possessed nano-sized grains and nanoporous structure. The KT film annealed at 500 °C showed high humidity sensitivity with nearly three orders change in the resistance during the relative humidity variation from 20% to 90%. The humidity-sensing behaviors of the thin films with annealing temperature are discussed.

The effect of poling treatment and crystal structure of PZT on fracture toughness and fatigue resistance

Empirical measurements of fracture toughness and fatigue strength were conducted for piezoelectric Pb(Zrx,Ti1 − x)O3 of various compositions such as tetragonal, MPB, and rhombohedral. Before the poling treatment the rhombohedral showed the highest fracture toughness, while the tetragonal revealed the lowest fracture toughness. After poling treatment, the fracture toughness measured by the pre-cracked SENB method decreased in all three compositions. The most remarkable decrease was observed in the tetragonal composition. However, when the indentation strength method was used the highest fracture toughness was observed in the tetragonal. The stress intensity factor relief due to microcracks around the indentation marks and the anisotropic internal stresses caused by domain alignment during the poling treatment were proposed as explanations for the comflicting results. Fatigue resistance was lowered by the compressive stress introduced during the poling treatment. The highest fatigue resistance was observed in the rhombohedral composition of low tetragonality, which exhibited low internal stress.

Sintering and piezoelectric properties of lead-free (K0.38Na0.58Li0.04)(Nb0.86Ta0.10Sb0.04)O3 ceramics doped with Fe2O3

Lead-free (K0.38Na0.58Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (KNLNTS) + x mol% Fe2O3 (x = 0 ~ 1) ceramics were prepared by conventional solid state reaction technique. The effect of Fe2O3 doping on the phase structure, microstructure and electrical properties of KNLNTS ceramics were studied. The addition of Fe2O3 was found to be effective in enhancing densification of KNLNTS ceramics. When x = 0.3, the piezoelectric constant d33 and planar piezoelectric coupling coefficient kp reached highest while maintaining a relatively high Curie point of 318 °C; d33 = 257 pC/N and kp = 52 %, which suggests that the ceramics are promising for electromechanical transducer and actuator applications.

PTCR Characteristics and Fabrication of Porous, Sb-Doped BaTiO3 Ceramics

Sb-doped BaTiO3 ceramics containing corn-starch were prepared by sintering at 1350°C for 1 h in air. In this study, the effect of corn-starch on positive temperature coefficient of resistivity (PTCR) characteristics and microstructures of Sb-doped BaTiO3 ceramics was investigated. It was found that the porosity and pore size increased and the grain size slightly decreased with increasing corn-starch content. XRD results showed the presence of BaTiO3 peaks only in the Sb-doped BaTiO3 ceramics with and without corn-starch. The PTCR jump of the Sb-doped BaTiO3 ceramics with corn-starch was over 106 and 1–2 orders higher than that of samples without corn-starch. The increase in the room-temperature resistivity with increasing corn-starch content was attributed mainly to the increase in the electrical barrier height of grain boundaries and the porosity as well as the partial decrease in the donor concentration of grains and the grain size. It was also noticed that the grain boundary resistivity contributed largely to the total resistivity of the Sb-doped BaTiO3—corn-starch ceramics.