Additional Oxygen Ordering in "La2NiO4.25" (La8Ni4O17): II. Structural Features

✍ Scribed by A. Demourgues; F. Weill; B. Darriet; A. Wattiaux; J.C. Grenier; P. Gravereau; M. Pouchard

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 302 KB
• Volume: 106
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1293

✦ Synopsis

On the basis of data obtained from the refinement of neutron diffraction experiments, the structural features of (\mathrm{La}{8} \mathrm{Ni}{4} \mathrm{O}{17}\left(\right.) " (\mathrm{LaNiO}{4.25}) ") are discussed. It is shown that the additional oxygen atoms in the (\mathrm{La}{2} \mathrm{O}{2}) layers form ( (\mathrm{O}{3}^{5-}) ) polyoxides including one delocalized hole. In the (\mathrm{NiO}{2}) planes, a periodic modulation of the equatorial (\mathrm{Ni}-\mathrm{O}) distances characterizes various electronic configurations of the nickel cations and a 2D charge density wave occurs, which is more pronounced at low temperature than at room temperature. A strong coupling between the (\left(\mathrm{O}{3}^{5}\right)) polyoxides and the (\mathrm{NiO}{2}) planes results from charge transfer mechanisms, which also account for the stabilization of monovalent nickel (\left(\mathrm{Ni}^{+}\right)) in this compound. The formation of (-\mathrm{Ni}^{+}-\left(\mathrm{O}{3}^{5-}\right)-\mathrm{Ni}^{+}-\left(\mathrm{O}{3}^{5-}\right)-) chains along given (\langle 111\rangle_{\top}) directions is correlated to the interstitial oxygen ordering previously evidenced. O1993 Academic Press, Inc.