Electron diffraction and high-resolution electron
microscopy of LaMnO
3-mages/gifchars/delta.gif" BORDER=0 > (0
mages/entities/le.gif">
mages/gifchars/delta.gif" BORDER=0 >
mages/entities/le.gif"> 0.25), obtainedby topotactic reduction of LaMnO
3, shows that an ordered pathway of anionic vacancies is only obtainedfor
mages/gifchars/delta.gif" BORDER=0 > = 0.25. La
4Mn
4O
11 is an eightfold superlattice of the perovskite-type structure due to the orderedintergrowth of three octahedral layers and one tetrahedral layer along the
b axis, according to the sequence...OOOTOOOT'... The reduced sa
mple exhibits ferro
magnetic behavior with
Tc mages/entities/ap.gif"> 50 K. The staircaseeffect, observed at low te
mperature, is discussed in ter
ms of the
magnetic ordering adopted in the octahedrallayers.