Relations between Oxygen Deficiency and Structures in the La-Sr-Cu-O System: III. Oxygen Content and Structure of the (La, Sr)8Cu8O16+δ Phase

✍ Scribed by Kenji Otzschi; Keiichi Koga; Yutaka Ueda

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 509 KB
• Volume: 115
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1995.1164

✦ Synopsis

The 8-8-16 (+\delta) phase (\left(\left(\mathrm{La}{1-x} \mathrm{Sr}{x}\right){8} \mathrm{Cu}{8} \mathrm{O}{16+\delta ;} ; \boldsymbol{x}=\mathbf{0 . 7 0}\right.) to 0.80()) was investigated precisely. The oxygen content increases with increasing partial pressure of oxygen, for example, (x=0.75 ; \delta=) 0.08 (annealed under (\mathrm{Ar}) at (810^{\circ} \mathrm{C}) ), (\delta=0.27) (quenched from (1050^{\circ} \mathrm{C}) in air; as-prepared), (\delta=2.29) (annealed in (\mathrm{O}{2}) at (800^{\circ} \mathrm{C}) ), and (\delta=2.54) (treated under (\mathrm{O}{2}) at high pressure (300 atm)). Xray diffraction study, however, disclosed that there are two distinct phases, an oxygen-poor phase ( (\delta \approx 0.0) : the 8-8-16 phase) and an oxygen-rich phase ( (\delta \geq 2.0); the 8-8-18 phase); as-prepared samples were a mixture of these two phases. These results disagree with those in the literature: (\delta=0.0) for as-prepared and (\delta=1.6) for (\mathrm{O}{2})-annealed. Structural refinements for the 8-8-16 and the 8-8-18 phases were carried out with (\boldsymbol{x}=\mathbf{0 . 7 7 5}) samples by the powder (\mathrm{X})-ray Rietveld method. They revealed oxygen insertion into the interstitial positions on the basal " (\mathrm{Cu}-\mathrm{O}) plane" in the 8-8-18 phase. Electrical resistivity data show semiconductor-like (8-8-16 phase) or metallic (8-8-18 phase) behavior. The weak temperature dependence of their magnetic susceptibility can be substantially explained by Pauli paramagnetism. O 1995 Academic Press, Inc.