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A Novel, Reactive Green Iron Sulfide (Sulfide Green Rust) Formed on Iron Oxide Nanocrystals
Jones, Christopher J.,Chattopadhyay, Soma,Gonzalez-Pech, Natalia I.,Avendano, Carolina,Hwang, Nina,Lee, Seung Soo,Cho, Minjung,Ozarowski, Andrew,Prakash, Arjun,Mayo, J. T.,Yavuz, Cafer,Colvin, Vicki. American Chemical Society 2015 Chemistry of materials Vol.27 No.3
<P>Iron oxide nanocrystals are of great scientific and technological interest. In this work, these materials are the starting point for producing a reactive nanoparticle whose surface resembles that of natural green rusts. Treatment of iron oxide nanoparticles with cysteamine leads to the reduction of iron and the formation of a brilliant green aqueous solution of nanocrystals rich in iron(II). These materials remained crystalline with magnetic and structural features of the original iron oxide. However, new low-angle X-ray diffraction peaks as well as vibrational features characteristic of cysteamine were found in the nanocrystalline product. X-ray absorption spectroscopy (XAS), X-ray photoemission (XPS) and Mössbauer spectroscopies indicated the presence of an iron(II)-rich phase with high sulfur content analogous to the iron–oxygen structures found in natural green rusts. Electron microscopy found that these structural components remained associated with the nonreduced iron oxide cores. These sulfur-rich analogs of natural green rusts are highly reactive and were able to rapidly degrade a model organic dye in water. This observation suggests possible actuation with a cysteamine treatment of inert and magnetic iron oxide particles at the point-of-use for environmental remediation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-3/cm5028942/production/images/medium/cm-2014-028942_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5028942'>ACS Electronic Supporting Info</A></P>
Multistage symmetry breaking in the breathing pyrochlore latticeLi(Ga,In)Cr4O8
Lee, S.,Do, S.-H.,Lee, W.-J.,Choi, Y. S.,Lee, M.,Choi, E. S.,Reyes, A. P.,Kuhns, P. L.,Ozarowski, A.,Choi, K.-Y. American Physical Society 2016 Physical Review B Vol.93 No.17
<P>We present magnetic susceptibility, dielectric constant, high-frequency electron spin resonance, Li-7 nuclear magnetic resonance, and zero-field muon spin relaxation measurements of LiACr(4)O(8) (A = Ga, In), towards realizing a breathing pyrochlore lattice. Unlike the uniform pyrochlore ZnCr2O4 lattice, both the In and the Ga compounds feature two-stage symmetry breaking: a magnetostructural phase transition with subsequent antiferromagnetic ordering. We find a disparate symmetry breaking process between the In and the Ga compounds, having different degrees of bond alternation. Our data reveal that the Ga compound with moderate bond alternation shows the concomitant structural and magnetic transition at T-S = 15.2 K, followed by the magnetic ordering at T-m = 12.9 K. In contrast, the In compound with strong bond alternation undergoes a thermal crossover at T* approximate to 20.1 K from a tetramer singlet to a dimer singlet or a correlated paramagnet with a separate weak magnetostructural transition at T-S = 17.6 K and the second antiferromagnetic ordering at T-m = 13.7 K. This suggests that the magnetic phases and correlations of the breathing pyrochlore lattice can be determined from the competition between bond alternation and spin-lattice coupling, thus stabilizing long-range magnetic ordering against a nonmagnetic singlet.</P>