Structural and superconducting properties of La2-xSrxCuO4 as a function of Sr content.
Phys Rev B Condens Matter 49:6 (1994) 4163-4175
High pressure synthesis and properties of the HgBa2 Can-1 Cun O2n+2+δ (n=1-6) superconductors
Physica C: Superconductivity and its applications 235-240:PART 1 (1994) 146-149
Abstract:
High-pressure high temperature synthesis has allowed us to prepare members of the new superconducting mercury cuprates series with n = 1-6. The variation of the structural and magnetic properties, oxygen content and Tc across the series, which appears to be the richest among the different superconducting cuprates, will be presented and discussed. Tc and the oxygen content δ increases with n from Hg-1201 (Tc=95K, δ=0.06) to a maximum of 135 K with δ=0.40 for Hg-1223. Structural refinement from neutron diffraction data on Hg-1245 showed a further decrease of δ = 0.30 in the high pressure as prepared compound (Tc= 101K). Tentatives to increase δ by a treatment under 200 bar of oxygen in Hg-1234, Hg-1245 and Hg-1256 showed instead a loss of oxygen from the overdoped as prepared samples. © 1994.Identity of planar defects in the 'infinite-layer' copper oxide superconductor
Nature 370:6488 (1994) 352-354
Abstract:
The 'infinite-layer' compound1-3 AcuO2 (where A stands for cations such as strontium or calcium), has the simplest structure of all superconducting copper oxides, with only bare cations separating the CuO2 planes. Accordingly, an understanding of the doping mechanism(s) that lead to superconductivity in this compound may facilitate the elucidation of the same phenomenon in the other copper oxide superconductors. Recently, Azuma and co-workers2,4 observed planar defects in an infinite-layer phase synthesized at high oxygen pressure, and proposed that the defects are A-cation deficient, and lead to superconductivity (with transition temperature T c≈ 100-110 K) in this compound. Here, based on quantitative X-ray and high-resolution electron-microscopic analysis of the planar defects in (Sr, Ca)CuO2, we propose that the defects consist of a corrugated Sr-O layer substituted for a CuO2 layer, with the incorporation of apical oxygen atoms (which are absent in the parent structure) at roughly half the available sites in the neighbouring Sr layers. This is equivalent to an insertion of a Sr3O2 ± x block in an otherwise infinite-layer sequence. The variable oxygen stoichiometry of our defect model can account for the occurrence of p-type superconductivity (following high-pressure oxygenation), n-type superconductivity (high-pressure reduction) or lack of superconductivity (high-pressure neutral-atmosphere annealing) in this system, depending on the synthesis conditions4. © 1994 Nature Publishing Group.Local configurations in ErBa2 Cu3 O6+x for 0.15≤x≤0.9
Physica C: Superconductivity and its applications 235-240:PART 2 (1994) 1261-1262
Abstract:
The NQR spectra of Cu in several ErBa2Cu3O6+x powder samples (0.1≤x≤0.9), characterized by particularly careful annealing, shows a limited number of frequency peaks. This fact is taken as evidence of a high degree of ordering of O(4) in the chain Cu(1) layer of the perovskite (formation of long full chains separated by empty chains as dictated by the stoichiometry), leading to a few regular patterns in the local configurations. © 1994.Phase diagram and phase separation in La2-x Srx CuO4+δ
Journal of Alloys and Compounds 207-208:C (1994) 206-212