On the cubic perovskites La{sub 0.2}Sr{sub 0.8}Cu{sub 0.4}M{sub 0.6}O{sub 3-y} (M = Co, Fe)

Journal Article · Wed Nov 01 00:00:00 EST 1995 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/0022-4596(95)80040-V· OSTI ID:486275

Genouel, R; Michel, C; Nguyen, N ^[1]

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1. Universite de Caen (France); and others

A new oxygen-deficient perovskite La{sub 0.2}Sr{sub 0.8}Cu{sub 0.4}M{sub 0.6}O{sub 3-y}(M = Co, Fe) has been synthesized that exhibits a large concentration of oxygen vacancies (0.3 {le} y {le} 0.58). Despite this, X-ray powder diffraction shows no superstructure of the primitive cell, indicating a random distribution of the vacancies on the oxygen sites. This result has been confirmed by electron diffraction and high-resolution microscopy, which show that most of the crystals exhibit the regular perovskite cell. In the cobalt phase, X-ray absorption spectroscopy at CoK-, CuK- and CuL{sub 3}-edges has shown that cobalt is in the Co(III) valence state even after oxygen annealings and that copper is in a mixed valence state, Cu(II)/Cu(III). In contrast, in the iron phase, which is less oxygen deficient than the cobalt phase, Moessbauer spectroscopy has shown that iron exhibits a mixed valence state, Fe(III)/Fe(IV). The conductivity of this new phase exhibits a transition from a semiconducting to a semimetallic behavior; it increases after oxygen annealings, in agreement with the increase in the hole density, i.e., the Cu(III) content.

• OSTI ID: 486275
• Journal Information: Journal of Solid State Chemistry, Vol. 119, Issue 2; Other Information: PBD: 1 Nov 1995
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
LANTHANUM OXIDES
STRUCTURAL CHEMICAL ANALYSIS
STRONTIUM OXIDES
COBALT OXIDES
IRON OXIDES
COPPER OXIDES
CRYSTAL DEFECTS
X-RAY DIFFRACTION
ELECTRON DIFFRACTION
ELECTRON MICROSCOPY
X-RAY SPECTROSCOPY
ABSORPTION SPECTROSCOPY
MOESSBAUER EFFECT
VALENCE
SEMICONDUCTOR MATERIALS
ANNEALING