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Solute structure and its evolution in supersaturated aqueous solutions are key clues to understand Ostwald’s step rule. Here, we measure the structural evolution of solute molecules in highly supersaturated solutions of KH2PO4 (KDP) and NH4H2PO4 (ADP) using a combination of electrostatic levitation and synchrotron X-ray scattering. The measurement reveals the existence of a solution-solution transition in KDP solution, caused by changing molecular symmetries and structural evolution of the solution with supersaturation. Moreover, we find that the molecular symmetry of H2PO4- impacts on phase selection. These findings manifest that molecular symmetry and its structural evolution can govern the crystallization pathways in aqueous solutions, explaining the microscopic origin of Ostwald’s step rule.The molecular symmetry of solute structure in aqueous solutions is a key clue to understand Ostwald’s step rule. Here, the authors show that molecular symmetry and its structural evolution can govern the crystallization pathways in aqueous solutions. [ABSTRACT FROM AUTHOR]

Applicability of spinel compounds is mainly governed by cation distribution in them. In the presented study, thermally induced cation ordering is found to influence the emission color of Mg 2 + , Fe 3 + co-doped ZnAl 2 O 4 spinel. Cation distribution is monitored through Mg K-edge, Fe L 2 , 3 -edge, O K-edge X-ray absorption near edge structure spectroscopy and X-ray diffraction analysis using synchrotron radiation. Thermal treatment provided sufficient energy to Zn 2 + , Mg 2 + , Al 3 + and Fe 3 + cations to redistribute themselves on tetrahedral and octahedral sites, and reduce the octahedral distortion, thereby gaining stability. Reduced inversion accompanied by decrease in oxygen vacancies, while increase in tetrahedral and octahedral site vacancies contributed toward more intense blue emission band and quenched yellow band, changing the emission color from bluish-white to blue. Correlation derived between cation ordering and luminescence upon thermal treatment predict Mg 2 + , Fe 3 + co-doped ZnAl 2 O 4 nanophosphors to be useful in thermal sensing applications. [ABSTRACT FROM AUTHOR]

We investigated the effect of tension on the stable α-phase formation of nylon 5,6 fibers with two different drawing speeds using two-dimensional transmission wide angle X-ray scattering (2D WAXS) measurement. In an ex-situ condition, i.e., after releasing the applied tension and temperature, the relative amount of the α-phase in the fibers was higher at a higher drawing speed (57 mm/min). On the contrary, the development of the α-phase seemed faster and stronger during in-situ elongation of the fiber at a lower drawing speed (38 mm/min). The γ-phase, rather than the α-phase, played a key role in this complex behavior. The mechanical properties of the nylon fibers elongated under slow drawing speed (38 mm/min) were better than those elongated under a higher drawing speed (57 mm/min). The mechanical properties were more consistent in the case of α-phase formation in an in-situ condition under applied tension on the nylon fibers. Detailed structural information was obtained by quantitative analysis of the 2D WAXS data using an in-situ fiber drawing device. [ABSTRACT FROM AUTHOR]