Piezoresponse and microstructure of BaTaO2N ceramics

Piezoresponse force microscopy was conducted on a polished slice of the perovskite oxynitride ceramic BaTaO₂N after ammonolysis at a bias voltage of?±?10?V. The ceramic surface was relatively porous because it was readily hydrolyzed by ambient humidity. While there was no piezoresponse on the surface of the ultrathin slice, a piezoresponse was clearly observed just below the surface of a thick slice. The response was enhanced in a denser sample. It increased with measuring voltage up to 7?V, and then gradually decreased up to 9?V. The response also gradually decreased with time but persisted even after 150?min at a measuring voltage of 6?V. Microstructural characterization revealed well-sintered grains, about 100?nm in size, in a relatively dense BaTaO₂N structure. High-porosity BaTaO₂N did not show any piezoresponse because its porous surface was easily hydrolyzed. A weak piezoresponse was observed for an electrically conductive slice obtained from deep inside a relatively dense BaTaO₂N ceramic after ammonolysis.     

Human impacts on groundwater flow and contamination deduced by multiple isotopes in Seoul City, South Korea

The influence of human activities on the flow system and contamination of groundwater were investigated in Seoul City, South Korea, one of the largest Asian cities, using a combination of isotopes (δD, T, δ¹⁵N, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr). Eighteen representative groundwater and river water samples, which were collected over a wide area of the city, were compared with previously reported data. The distribution of stable isotopes (δD and δ¹⁸O) with groundwater potential data shows that recharged groundwater from either the surrounding mountainous area as well as the Han River and other surface streams discharged towards the northern-central part of the city, where a subway tunnel pumping station is located. It is suggested from T values (3.3 to 5.8 T.U.) that groundwater was recharged in the last 30 to 40 years. The δ³⁴S and δ¹⁵N of SO₄²⁻ and NO₃⁻ data were efficiently used as indicators of contamination by human activities. These isotopes clarified that the contribution of anthropogenic contaminants i.e., industrial and household effluents, waste landfills, and fertilizers, are responsible for the enrichment by SO₄²⁻ (> 30 ppm as SO₄²⁻) and NO₃⁻ (> 20 ppm as NO₃⁻) of groundwater. The ⁸⁷Sr/⁸⁶Sr values of groundwater vary (0.71326 to 0.75058) in accordance with the host rocks of different origins. Mineral elements such as Ca are also suggested to be derived naturally from rocks. The groundwater under Seoul City is greatly affected by transportation of pollutants along the groundwater flow controlled by subway tunnel pumping, contributing to the degradation of water quality in urbanized areas.     

Erratum to “Effects of intensive urbanization on the intrusion of shallow groundwater into deep groundwater: Examples from Bangkok and Jakarta”

Asian megacities have severe pollution problems in both coastal and urban areas. In addition, the groundwater potential has decreased and land subsidence has occurred because of intensive groundwater pumping in urban areas. To prevent the adverse effects of urbanization on groundwater quality, it is necessary to confirm the changes in groundwater flow and contaminant transport caused by urbanization. We examined the effects of urbanization on contaminant transport in groundwater. The research areas were located around Bangkok, Thailand, and akarta, Indonesia, cities with populations of approximately 8 and 12 million, respectively. Each metropolitan city is located on a river delta and is adjacent to a bay. We measured the water level and collected water samples at boreholes at multiple depths (100 to 200 m) in 2004 and 2006 in Bangkok and Jakarta, respectively. The current hydraulic potential is below sea level in both cities because of prior excess abstraction of groundwater. As a result, the direction of groundwater flow is now downward in the coastal area. The Cl⁻ concentration and δ¹⁸O distributions in groundwater suggest that the decline in hydraulic potential has caused the intrusion of seawater and shallow groundwater into deep groundwater. Concentrations of Mn and NO3⁻-N in groundwater suggest the intrusion of these contaminants from shallow to deep aquifers with downward groundwater flow and implies an accumulation of contaminants in deep aquifers. Therefore, it is important to recognize the possibility of future contaminant transport with the discharge of deep groundwater into the sea after the recovery of groundwater potential in the coastal areas.     

Comprehensive studies on the stabilities of a-In-Ga-Zn-O based thin film transistor by constant current stress

Stability under constant current stress, along with hysteresis characteristics, was studied for a-In-Ga-Zn-O thin-film transistors (TFTs) in several atmospheres and at several temperatures. Unannealed TFTs showed rather large instability; i.e., large hysteresis in transfer curves (ΔV_G > 0.8 V) and large positive threshold voltage shift (ΔV_th > 10 V for 50 h tests at 5 µA) with deterioration of subthreshold voltage swing was observed. The instability for the unannealed TFT had a strong dependence on the stress atmosphere and the stress temperature, which suggests that trap states generated by the stress test is related to oxygen vacancy formed by breaking weak chemical bonds. Wet annealing improved stability; the hysteresis disappeared and the ΔV_th was reduced to < 2 V. The improvement is considered to be related to the reduction of weak chemical bonds by wet annealing with the strong oxidation power of water molecules.     

Highly accessible or decrystallized cotton by chemical methods

To obtain highly accessible cotton by cyanoethylation with acrylonitrile after pretreatment with swelling agents, the effect of various swelling agents was examined. Swelling agents such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ethylamine, triethylamine, ethylenediamine, piperazine, benzyltrimethylammonium hydroside (BTMOH), urea, dimethyl sulfoxide, dimethylformamide, zinc chloride, and liquid ammonia were examined. It was found that the sodium hydroxide pretreatment or the dual pretreatment with either potassium hydroxide, ethylenediamine, or BTMOH, and sodium hydroxide prior to acrylonitrile treatment gave modified cottons having moisture regain as high as 14%. In such cases, maximum values of moisture regain were observed at the degrees of cyanoethylation of 5–8%.     

Antimutagenic properties of lactic acid-cultured milk on chemical and fecal mutagens

The antimutagenic properties of milk cultured with Lactobacillus bulgaricus and Streptococcus thermophilus were examined using streptomycin-dependent strains of Salmonella in an in vitro assay system. The mutagens utilized for testing included 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide, 4-nitroquinoline-N-oxide, and fecal mutagenic extracts from cats, monkeys, dogs, and other mammals. Both types of cultured milk exhibited antimutagenic activity on all mutagens used. Antimutagenic activities of the cultured milks with 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide and 4-nitroquinoline-N-oxide increased with incubation time but were thermolabile beyond 55 degrees C for 10 min.     

Present and future of piezoelectric single crystals and the importance of B-site cations for high piezoelectric response

High quality piezoelectric single crystals, such as Pb(Zn_1/3 Nb_2/3)O₃-PbTiO₃ (PZNT) and Pb(Mg _1/3Nb_2/3)O₃-PbTiO₃ (PMNT), have been investigated, and, because their piezoelectric properties are greatly superior to those of Pb(Zr_1-xTi_x)O₃ (PZT) ceramics, they have been used for certain transducer applications since the late 1990s. The present situation for these relaxor-PT (lead titanate) single crystals is summarized. In this review, some possible high Tc > 200°C single crystals are also introduced. Single crystals of Pb(In_1/2Nb_1/2)O₃-PbTiO₃ (PINT) binary system and Pb(Mg_1/3Nb_2/3)O₃ -Pb(Sc_1/2Nb_1/2)O₃-PbTiO₃ (PSMNT) tertiary system have been synthesized, and their electrical properties are reported. In addition, a novel guiding principle for discovering excellent piezoelectric materials, namely the presence of low molecular mass B-site ions that can enter the lead-perovskite Pb(B'B")O₃ structure, is introduced