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Interest in the transition metal oxides with perovskite related
structures goes back to the 1950s when the sodium tungsten bronzes
NaxWO3 were shown to be metallic [1 ], the system Lal_xSr~MnO3 was
found to contain a ferromagnetic conductive phase [2], and
La0.sSr0.sCoO3 was reported to be a ferromagnetic metal, but with a
peculiar magnetization of 1.5 #a/Co atom [3]. Stoichiometric oxide
perovskites have the generic formula AMO3 in which the A site is at
the center of a simple cubic array of M sites; the oxide ions form
(180 4)) M O M bridges to give an MO3 array of corner shared MO6/2
octahedra and the larger A cations have twelvefold oxygen
coordination. Mismatch between the A O and M O equilibrium bond
lengths introduces internal stresses. A compressive stress on the
MO3 array is accommodated by a lowering of the M O M bond angle
from 180 to (180 4)); a tensile stress on the M O M bonds is
accommodated by the formation of hexagonal polytypes [4].
Interest in the transition metal oxides with perovskite related
structures goes back to the 1950s when the sodium tungsten bronzes
NaxWO3 were shown to be metallic [1 ], the system Lal_xSr~MnO3 was
found to contain a ferromagnetic conductive phase [2], and
La0.sSr0.sCoO3 was reported to be a ferromagnetic metal, but with a
peculiar magnetization of 1.5 #a/Co atom [3]. Stoichiometric oxide
perovskites have the generic formula AMO3 in which the A site is at
the center of a simple cubic array of M sites; the oxide ions form
(180 4)) M O M bridges to give an MO3 array of corner shared MO6/2
octahedra and the larger A cations have twelvefold oxygen
coordination. Mismatch between the A O and M O equilibrium bond
lengths introduces internal stresses. A compressive stress on the
MO3 array is accommodated by a lowering of the M O M bond angle
from 180 to (180 4)); a tensile stress on the M O M bonds is
accommodated by the formation of hexagonal polytypes [4].
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