Professor Paolo G. Radaelli OSI

Abstract:

We report the first experimental observation of a pressure-induced structural phase transition in the RNiO3 series. At ≈ 40 kbar, the space group of NdNiO3 changes from Pbnm (orthorhombic) to the more symmetrical R3̄c (rhombohedral). This experiment confirms our previous results on PrNiO3 indicating that the symmetry of the structure increases with pressure.

Abstract:

It is shown that the superconducting and structural properties of Tl2Ba2CuO6+δ depend on at least two defects. The Tl/Cu ratio used during synthesis determines the concentration of a defect that is likely to be Cu substitution on the Tl site, based on previously published work that proves the existence of such a defect. The structure exhibits a smaller orthorhombic strain, or tetragonal symmetry, for high concentrations of this defect. Tc tends to be lowered by this defect. An oxygen interstitial defect in the Tl-O double layer has a more pronounced effect on Tc, allowing the compound to be overdoped as the concentration of this defect increases. Features in the diffraction data also suggest the existence of a third defect which may involve the filling of oxygen vacancies at an oxygen site in the structure during early stages of oxygenation.

Abstract:

The n = 3 and n = 5 members of the homologous series Srn-1,Cun+1O2n have been synthesised by a high-pressure, high-temperature technique and characterized by X-ray powder diffraction and electron microscopy as well as EDS microanalysis. The solubility range of Sr4-xNdxCu6O10 solid solution was found to be <0.1. The crystal structure of Sr4Cu6O10 was refined from neutron powder diffraction data.