The microstructural development of crystalline-oriented (K 0.5 Na 0.5 )NbO 3 (KNN)-based piezoelectric ceramics during sintering was investigated. The addition of CuO as a sintering aid was found to be effective for fabricating highly oriented and dense KNN ceramics. KNN specimens containing 0.5-1.0 mol% CuO sintered at 11001C for 1 h were found to have relative densities and pseudo-cubic {100} orientation degrees of 95% or higher. In the early stages of sintering, KNN is formed in the reaction between complementary reactants NaNbO 3 and KNbO 3 , after which oriented grain growth proceeds at a relative density of more than 90%. In addition, the results of transmission electron microscopy observation showed that textured KNN ceramics have a unique pectinate-like domain structure with domain walls consisting of {101} planes. 1951J ournal

We fabricated Cu2Sn1− x Ge x S3 (CTGS) solar cells with a graded bandgap structure in order to improve their photovoltaic performance. Bandgap gradation was formed by changing the Ge/Sn ratio in the depth direction of the CTGS layers. The composition profile of each sample was measured by secondary ion mass spectrometry, and we confirmed that the Ge/Sn ratio near the buffer layer was lower than that near the back electrode. This means that the bandgap increases with depth from the surface. The performance of the cells was improved to over 6.7% in conversion efficiency.

The work reported herein demonstrated that nanopipes can be formed via a surfactant effect, in which boron impurities preferentially migrate to semipolar and nonpolar facets. Approximately 3 μm-thick GaN layers were grown using halogen-free vapor phase epitaxy. All layers grown in pyrolytic boron nitride (pBN) crucibles were found to contain a high density of nanopipes in the range of 1010 to 1011 cm−2. The structural properties of these nanopipes were analyzed by X-ray rocking curve measurements, transmission electron microscopy, and three-dimensional atom probe (3DAP) tomography. The resulting 3DAP maps showed nanopipe-sized regions of boron segregation, and these nanopipes were not associated with the presence of dislocations. A mechanism for nanopipe formation was developed based on the role of boron as a surfactant and considering energy minima. A drastic reduction in the nanopipe density was achieved upon replacing the pBN crucibles with tantalum carbide-coated carbon crucibles. Consequently, we have confirmed that nanopipes can be formed solely due to surface energy changes induced by boron impurity surface segregation. For this reason, these results also indicate that nanopipes should be formed by other surfactant impurities such as Mg and Si.

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Lithium cobalt dioxide (LiCoO 2) belongs to a family of layered CoO 2-based materials and has considerable interests in both fundamental physics and technological applications in lithium-ion batteries. We report the results of structural, electrochemical, magnetic susceptibility (χ), electron paramagnetic resonance (EPR), and muon-spin rotation and relaxation (μSR) measurements on powder Li x 0 CoO 2 samples, where the nominal Li/Co ratios (x 0) were 0.95, 1.00, 1.02, 1.05, and 1.10, respectively. Structural, electrochemical, and χ measurements suggested that the sample with x 0 = 1.02 is very close to single stoichiometric LiCoO 2 (ST-LCO) phase and that the Co ions in the x 0 = 1.02 sample are in a nonmagnetic low-spin state with S = 0 (t 6 2g). However, both EPR and μSR revealed that the x 0 = 1.02 (ST-LCO) sample includes a large amount of nonordered magnetic phase in the temperature (T) range between 100 and 500 K. The volume fraction of such magnetic phase was found to be ß45 vol% at 300 K by μSR, indicating an intrinsic bulk feature for ST-LCO. In fact, structural and photoelectron spectroscopic analyses clearly excluded the possibility that the nonordered magnetism is caused by impurities, defects, or surfaces. Because EPR and μSR sense static and dynamic nature of local magnetic environments, we concluded that Co spins in ST-LCO are fluctuating in the EPR and μSR time-windows. We also proposed possible origins of such nonordered magnetism, that is, a spin-state transition and charge disproportionation.