La2MO4+δ (M=Cu, Ni, Co): Phase Separation and Superconductivity Resulting from Excess Oxygen Defects
The structural, superconducting and normal-state properties of La2MO4+δ (M=Cu, Ni, Co) were studied by neutron powder diffraction, thermogravimetric analysis and resistivity measurements. La2CuO4+δ was found to undergo phase separation near room temperature into antiferromagnetic La2CuO4 and superconducting La2CuO4.08. Single-phase, metallic, superconducting La2CuO4.08 was prepared under 25 kbar of O2 at 500 °C. The excess oxygen present as O= ions provides a doping mechanism analogous to alkaline-earth metal ion substitution.
La2NiO4+δ and La2CoO4+δ undergo a similar phase separation for 0.02<δ<0.12 and 0<δ<0.16, respectively. The structure of the interstitial excess oxygen defect was determined for a single-phase La2NiO4.18 sample. A different excess oxygen defect forms for material with 0≤δ≤0.02. All stoichiometric (δ=0) compounds have the same Cmca orthorhombic structure and are semiconducting and antiferromagnetic.
KeywordsExcess Oxygen Neutron Powder Diffraction Oxygen Stoichiometry Oxygen Defect High Oxygen Pressure
Unable to display preview. Download preview PDF.
- 5.B. Dabrowski, D.G. Rinks, J.D. Jorgensen, K. Zhang and C.U. Segre, Bull. Amer. Phys. Soc. 33, 557 (1988).Google Scholar
- 11.J.E. Schirber, E.L. Venturini, B. Morosin, J.F. Kwak, D.S. Ginley, and R.J. Baughman, Mater. Res. Soc. Symp. Proc. Vol. 22, 479 (1988).Google Scholar
- 12.P.Ganguly, in. “Advances in Solid State Chemistry” (C.N.R. Rao, Ed.). p. 135ff, Indian National Scince Academy, New Delhi (1986).Google Scholar
- 17.B. Dabrowski, D.G. Hinks, J.D. Jorgensen and D.R. Richards (to be published in Mater. Res. Soc. Symp. Proc.)Google Scholar