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Smaller Grain Size (smaller + grain_size)
Selected AbstractsInterfacial Microstructure of Chromium Oxide Coatings,ADVANCED ENGINEERING MATERIALS, Issue 7 2007X. Pang This paper presents a study of chromium oxide coatings' interfacial microstructure and structural properties affecting coating performance. Amorphous chromium and chromium oxide layers about 100 nm thick were detected at the Cr/steel and the Cr/coating interfaces, providing a solution for depositing thicker mechanically stable coatings with improved hardness, smaller grain size, and smooth surface. [source] Preparation and Memory Performance of a Nanoaggregated Dispersed Red 1-Functionalized Poly (N -vinylcarbazole) Film via Solution-Phase Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Xiao-Dong Zhuang Abstract A nanoaggregated dispersed red 1-grafted poly(N -vinylcarbazole) (abbreviated PVDR) is self-assembled via ,,, stacking interactions of the carbazole groups in the polymer system after adding a solution of PVDR in N,N -dimethylformamide to dichloromethane. Upon self-assembly, the nanoaggregated PVDR film displays helical columnar stacks with large grain sizes, whereas a non-aggregated PVDR film exhibits an amorphous morphology with smaller grain size. A write-once read-many-times (WORM) memory device is shown whereby a pre-assembled solution of PVDR is spin-coated as the active layer and is sandwiched between an aluminum electrode and an indium-tin-oxide (ITO) electrode. This device shows very good memory performance, with an ON/OFF current ratio of more than 105 and a low misreading rate through the precise control of the ON and OFF states. The stability of the nanoaggregated PVDR device is much higher than that of the non-nanoaggregated PVDR device. This difference in device stability under constant voltage stress can be mainly attributed to the difference in the film crystallinity and surface morphology. No degradation in current density was observed for the ON- and OFF-states after more than one hundred million (108) continuous read cycles indicating that both states were insensitive to the read cycles. These results render the nanoaggregated PVDR polymer as promising components for high-performance polymer memory devices. [source] Patterns of woody plant species richness in the Iberian Peninsula: environmental range and spatial scaleJOURNAL OF BIOGEOGRAPHY, Issue 10 2008Ole R. Vetaas Abstract Aim, Climate-based models often explain most of the variation in species richness along broad-scale geographical gradients. We aim to: (1) test predictions of woody plant species richness on a regional spatial extent deduced from macro-scale models based on water,energy dynamics; (2) test if the length of the climate gradients will determine whether the relationship with woody species richness is monotonic or unimodal; and (3) evaluate the explanatory power of a previously proposed ,water,energy' model and regional models at two grain sizes. Location, The Iberian Peninsula. Methods, We estimated woody plant species richness on grid maps with c. 2500 and 22,500 km2 cell size, using geocoded data for the individual species. Generalized additive models were used to explore the relationships between richness and climatic, topographical and substrate variables. Ordinary least squares regression was used to compare regional and more general water,energy models in relation to grain size. Variation partitioning by partial regression was applied to find how much of the variation in richness was related to spatial variables, explanatory variables and the overlap between these two. Results, Water,energy dynamics generate important underlying gradients that determine the woody species richness even over a short spatial extent. The relationships between richness and the energy variables were linear to curvilinear, whereas those with precipitation were nonlinear and non-monotonic. Only a small fraction of the spatially structured variation in woody species richness cannot be accounted for by the fitted variables related to climate, substrate and topography. The regional models accounted for higher variation in species richness than the water,energy models, although the water,energy model including topography performed well at the larger grain size. Elevation range was the most important predictor at all scales, probably because it corrects for ,climatic error' due to the unrealistic assumption that mean climate values are evenly distributed in the large grid cells. Minimum monthly potential evapotranspiration was the best climatic predictor at the larger grain size, but actual evapotranspiration was best at the smaller grain size. Energy variables were more important than precipitation individually. Precipitation was not a significant variable at the larger grain size when examined on its own, but was highly significant when an interaction term between itself and substrate was included in the model. Main conclusions, The significance of range in elevation is probably because it corresponds to several aspects that may influence species diversity, such as climatic variability within grid cells, enhanced surface area, and location for refugia. The relative explanatory power of energy and water variables was high, and was influenced by the length of the climate gradient, substrate and grain size of the analysis. Energy appeared to have more influence than precipitation, but water availability is also determined by energy, substrate and topographic relief. [source] Addition of a Sr, K, Nb (SKN) Combination to PZT(53/47) for High Strain ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007Niall J. Donnelly A lead zirconate titanate composition incorporating the dopants Sr, K, and Nb (SKN) in the specific ratio 4:1:3 has been studied. In principle, the SKN should act as a donor dopant but since its addition reduced the grain size from 11.4 ,m (for 1% SKN) to 1.5 ,m (for 5% SKN), the overall effect was found to be more complicated. It was observed that the addition of SKN reduced the Curie temperature, by 16°C/mol (%) and broadened the dielectric peak. X-ray measurements further suggested that the ceramic was a mixture of rhombohedral and tetragonal phases and that the room temperature c/a ratio of the tetragonal phase decreased with SKN addition. The piezoelectric coefficient d33, determined from high field unipolar drives, gave an optimum value of 779 pm/V for the 0.02 SKN compositions, which also exhibited a relatively high Curie temperature of 356°C. Competing effects of enhanced domain wall mobility from donor doping and reduced mobility due to smaller grain size may explain the observed compositional variation in the measured material properties. Materials based on this composition are attractive for high performance piezoelectric actuator applications such as fuel injection. [source] Improvement of Microwave Loss Tangent and Tunability of Ba0.55Sr0.45TiO3/MgO Composites Using the Heterogeneous Precipitation MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Rui-Hong Liang Ba0.55Sr0.45TiO3/MgO composites were successfully prepared by the heterogeneous precipitation method and their structural, surface morphological, tunable properties, and dielectric properties at microwave frequency were systemically investigated. Compared with the sample prepared by the traditional solid-state method, the sample prepared by the heterogeneous precipitation method exhibits a smaller grain size, more uniform microstructure, higher tunability, and lower microwave loss, and these properties are very beneficial to the development of the microwave tunable devices application. Moreover, the effects of La2O3 doping on the dielectric and tunable properties of BST/MgO composites are investigated. The result shows that the La3+ -doped sample has higher tunability and lower microwave loss than the undoped one. [source] Electric Field-Dependent Dielectric Properties and High Tunability of Porous Ba0.5Sr0.5TiO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007Yuanyuan Zhang Porous Ba0.5Sr0.5TiO3 (BST) ceramics were fabricated by the traditional solid-state reaction process, and their structural, microstructural, dielectric, and tunability properties were systemically investigated. Compared with the fully dense BST samples, porous samples exhibit smaller grain sizes, a more uniform microstructure, and much lower dielectric constants, while at the same time, exhibiting little increase in tunability, which is beneficial to the development of microwave-tunable applications. At a frequency of 10 kHz and a temperature of 18°C, as porosity increased from 0% to 28.8%, the dielectric constant of the BST ceramics (under zero bias field) decreased from ,r(0),1690 to ,r(0),990, while the dielectric losses were still less than 0.2%, and the tunability increased from 17.6% to 19.6% (2.6 kV/mm). [source] | ||||||||||