Professor Paolo G. Radaelli OSI

Abstract:

The phase-diagram of Ca2-x.SrxRuO4 has been studied by several diffraction techniques as function of concentration, temperature, pressure and magnetic field. The substitution of Sr through the smaller Ca induces a series of structural phase transitions with a strong impact on the physical properties. The spin triplet superconductor Sr 2RuO4 exhibits an undistorted crystal structure, and the Mott-insulator Ca2RuO4 strong structural distortions. For intermediate structural distortions samples stay metallic but with outstanding properties. Throughout the phase diagram we find a close coupling between the crystal structure on one side and magnetic and electronic behavior on the other side. © 2005 Materials Research Society.

Abstract:

We have used electron diffraction and neutron powder diffraction to elucidate the structural properties of superconducting NaxCoO 2•yD2O over a wide compositional range. Our measurements show that superconducting samples exhibit a number of supercells ranging from to , but the predominant modulation, observed also in the neutron data, is a double hexagonal cell with dimensions 2a × 2a × c. Rietveld analysis reveals that D2O is inserted between CoO 2 sheets to form a layered network of NaO6 triangular prisms. Our model removes the need to invoke a 5 K superconducting point compound and suggests that a solid solution of Na is possible within a relatively constant amount of water y. © IOP Publishing Ltd.