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 · Tue Oct 31 23:00:00 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, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 119; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

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