Ideal Value (ideal + value)

Distribution by Scientific Domains

Selected Abstracts

On the capability of revealing the pseudosymmetry of the chalcopyrite-type crystal structure

D. Abou-Ras
Abstract The tetragonal crystal-structure type of chalcopyrites (chemical formula AIBIIICVI2) is a superstructure of sphalerite type. The c /a ratio differs generally from the ideal value 2, i.e., the crystal structure is pseudocubically distorted. For CuInSe2 and CuGaSe2 thin films, simulations demonstrate that it is theoretically possible to reveal the tetragonality in electron backscatter-diffraction (EBSD) patterns for CuGaSe2, whereas it may not be possible for CuInSe2. EBSD experiments on CuGaSe2 thin films using the "Advanced Fit" band-detection method show that it is possible to extract accurate misorientation-angle distributions from the CuGaSe2 thin film. Pole figures revealing the texture of the CuGaSe2 thin film are shown, which agree well with X-ray texture measurements from the same layer. ( 2008 WILEY -VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Water sorption, glass transition, and protein-stabilizing behavior of an amorphous sucrose matrix combined with various materials

Koreyoshi Imamura
Abstract The effects of various additives on the physical properties of an amorphous sugar matrix were compared. Amorphous, sugar,additive mixtures were prepared by freeze-drying and then rehumidified at given RHs. Sucrose and eighteen types of substances were used as the sugar and the additive, respectively, and water sorption, glass-to-rubber transition, and protein stabilization during freeze-drying for the various sucrose,additive mixtures were examined. The additives were categorized into two groups according to their effects on Tg and water sorption. Presence of polysaccharides, cyclodextrins, and polymers (large-sized additives) resulted in a decrease in equilibrium water content from the ideal value calculated from individual water contents for sucrose and additive, and in contrast, low MW substances containing ionizable groups (small-ionized additives) resulted in an increase. The increase in Tg by the addition of large-sized additives was significant at the additive contents >50,wt.% whereas the Tg was markedly increased in the lower additive content by the addition of small-ionized additives. The addition of small-ionized additives enhanced the decrease in Tg with increasing water content. The protein stabilizing effect was decreased with increasing additive content in the cases of the both groups of the additives. 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4669,4677, 2010 [source]

Analysis of the local structure of InN with a bandgap energy of 0.8 and 1.9 eV and annealed InN using X-ray absorption fine structure measurements

Takao Miyajima
Abstract We compared the local structure around In atoms in microwave-excited MOCVD- and MBE-grown InN film which indicates an absorption edge at 1.9 and 0.8 eV, respectively. The co-ordination numbers of the 1st-nearest neighbor N atoms and the 2nd-nearest neighbor In atoms for MBE-grown InN were n(N) = 3.9 0.5 and n(In) = 12.4 0.9, which are close to the ideal value of n(N) = 4 and n(In) = 12 for InN without defects, respectively. By thermal annealing, the structure of MBE-grown InN was changed from InN to In2O3, and the absorption edge was changed from 0.8 to 3.5 eV. However, the microwave-excited MOCVD-grown InN had no structure of In2O3, and had the reduced co-ordination numbers of the 2nd-nearest neighbor In atoms of n(In) = 10.6-11.7. From these results, we conclude that the origin of the 1.9-eV absorption edge of InN is the imperfections (defects) of the In lattice sites of InN, rather than the generation of In2O3, which has a bandgap energy of 3.5 eV. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ternary fluorides BaMF4 (M = Zn, Mg and Mn) at low temperatures

Jose Maria Posse
Ternary fluorides BaMF4 (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10,K using synchrotron and laboratory powder and single-crystal diffraction. The first two compounds are stable down to 10,K, while the third one undergoes a phase transition to an incommensurately modulated structure at approximately 250,K. The modulated phase is stable down to 10,K. The magnetic anomalies at 45 and 27,K observed previously in BaMnF4 are exclusively reflected in the behavior of the , component of the q vector, which assumes an irrational value of approximately 0.395,,1 at the temperature corresponding to the onset of the magnetic ordering and then stays constant down to 10,K. Mn,Mn distances do not indicate any structural response to the magnetic ordering. The formation of the modulated phase can be explained on the basis of simple geometrical criteria. The incorporation of the large Mn cation in the octahedral sheets implies an increase of the cavity in which the Ba ion is incorporated. This leads to the formation of the modulated structure to adapt the coordination sphere around Ba in such a way that the bond-valence sums can be kept close to the ideal value of two. With further lowering of the temperature, the charge balance around the Ba ion requires an increasingly anharmonic character of the modulation function of Ba, until finally at 10,K a crenel-like shape is assumed for the modulation of this atom. [source]