Oxygen Nonstoichiometry and Its Effect on the Structure of LaNiO3

✍ Scribed by Soma Rakshit; P.S. Gopalakrishnan

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 159 KB
• Volume: 110
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1994.1130

✦ Synopsis

(\mathrm{LaNiO}{3}) is known to have a slightly distorted perovskite structure, making it hexagonal with cell parameters (a=5.455 \AA) and (c=6.561 \AA). In this paper it is shown that stoichiometric (\mathrm{LaNiO}{3}) is an ideal cubic perovskite with cell parameter (a=3.851 \AA). The cubic (\mathrm{LaNiO}{3}) loses a little oxygen when heated at higher temperatures and transforms gradually to the hexagonal phase. Such an oxygen deficiency and structural change also take place whenever a flux of (\mathrm{Na}{2} \mathrm{CO}{3}) is used for the preparation of (\mathrm{LaNiO}{3}). This is due to incorporation of a little sodium impurity into the lattice during the preparation. Another interesting feature of the transformation is that it undergoes a transient tetragonal phase. (\mathrm{LaNiO}{3}) containing sodium impurity and the cubic (\mathrm{LaNiO}{3}) differ in the manner in which they are reduced by hydrogen; the former is converted to (\mathrm{La}{2} \mathrm{Ni}{2} \mathrm{O}{5}) and then to (\mathrm{LaNiO}{2}), whereas the latter gives (\mathrm{La}{2} \mathrm{Ni}{2} \mathrm{O}{5}) and then a mixture of (\mathrm{La}{2} \mathrm{O}_{3}) and (\mathrm{Ni}). 1994 Academic Press, Inc.