The Local Structure of High-Temperature Superconductors

We show how x-ray absorption fine structure (XAFS) has been successfully used in the determination of the local crystal structure of high-temperature superconductors, with advantages over traditional diffraction techniques. We review the experimental results that yielded the first evidence for an axial-oxygen-centered lattice instability connected with the superconductivity transition. The interpretation of this instability in terms of a dynamical tunneling model suggests the presence of polarons in these materials. XAFS on Tl[sub 2]Ba[sub 2]CuO[sub 6] and other Tl-based superconductors indicate the presence of local instabilities in the CuO[sub 2] planes of these materials, in addition to axial-oxygen instabilities

Tris(tetrabutylammonium) tris(nitrato-κ2O,O′)tetrakis(thiocyanato-κN)thorium(IV)

The title compound, (C16H36N)3[Th(NCS)4(NO3)3], was obtained from the reaction of Th(NO3)4·5H2O with (Bu4N)(NCS). The ThIV atom is in a ten-coordinate environment of irregular geometry, being bound to the N atoms of the four thiocyanate ions and to three bidentate nitrate ions. The average Th—N and Th—O bond lengths are 2.481 (10) and 2.57 (3) Å, respectively

Experimental Speciation of Plutonium(IV) in Natural Seawater

International audienceSolubility, migration, and bioavailability of plutonium is lacunar because experimental evidences are missing. We report here on X-ray Absorption Spectroscopy of plutonium in natural seawater. The observed valence state is +IV and its speciation corresponds to PuO2 type colloids. Furthermore, aging of the solution shows a gradient of ordering from hydroxide colloidal species to more crystalline PuO2 colloids