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Ba(BO2OH) – A Monoprotonated Monoborate from Hydroflux Showing Intense Second Harmonic GenerationLi, Yuxi, Hegarty, Peter A., Rüsing, Michael, Eng, Lukas M., Ruck, Michael 30 May 2024 (has links)
Pure samples of colorless, air-stable Ba(BO2OH) crystals were obtained from Ba(NO3)2 and H3BO3 under the ultra-alkaline conditions of a KOH hydroflux at about 250 °C. The product formation depends on the water-base molar ratio and the molar ratio of the starting materials. B(OH)3 acts as a proton donor (Brønsted acid) rather than a hydroxide acceptor (Lewis acid). Ba(BO2OH) crystallizes in the non-centrosymmetric orthorhombic space group P212121. Hydrogen bonds connect the almost planar (BO2OH)2− anions, which are isostructural to HCO3−, into a syndiotactic chain. IR and Raman spectroscopy confirm the presence of hydroxide groups, which are involved in weak hydrogen bonds. Upon heating in air to about 450 °C, Ba(BO2OH) dehydrates to Ba2B2O5. Moreover, the non-centrosymmetric structure of Ba(BO2OH) crystals was verified with power-dependent confocal Second Harmonic Generation (SHG) microscopy indicating large conversion efficiencies in ambient atmosphere.
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Approximate icosahedral symmetry of α-Al(Fe,Mn,Cr)Si in electron backscatter diffraction analysis of a secondary Al-Si casting alloyBecker, Hanka, Leineweber, Andreas 07 August 2023 (has links)
Frequent systematic misindexing of electron backscatter diffraction patterns with five differently oriented pseudosymmetric solutions was observed for the cubic α-Al(Fe,M)Si phase with M = Mn, Cr encountered in secondary Al-Si casting alloy. That misindexing can be ascribed to the close structural relationship of the cubic crystal structure of α-Al(Fe,M)Si to that of the corresponding icosahedral quasicrystal. Robust identification of the correct among the five nearby solutions during automatic indexing can be achieved, which sensitively depends on the accuracy of Kikuchi-band detection applying Hough-space related indexing methods. Based on the correct crystallographic orientation solution, facets of the particles with bulk polyhedral and Chinese script morphology were determined to be {110} planes. Likewise, the habit planes of the α-Al(Fe,M)Si phase particles located at the naturally occurring oxide film are {110} planes.
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