A new family of misfit layered oxides with double rock salt layers Bi{sub {alpha}}(A{sub 0.75{+-}{var_epsilon}}Bi{sub 0.25{+-}{var_epsilon}}O){sub (3+3x)/2}MO{sub 2} (A = Ca, Sr and M = Co, Cr)
Journal Article
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· Journal of Solid State Chemistry
- ISMRA-Univ. de Caen (France). Lab. CRISMAT
A series of Bi-based new misfit layered oxides--Bi{sub 0.35}(Sr{sub 0.74}Bi{sub 0.26}O){sub 1.72}CoO{sub 2}, Bi{sub 0.35}(Ca{sub 0.75}Bi{sub 0.25}O){sub 1.8} CoO{sub 2}, Bi{sub 0.08}Pb{sub 0.35}(Sr{sub 0.68}Bi{sub 0.32}O){sub 1.62}CoO{sub 2}, Bi{sub 0.18}Pb{sub 0.4}(Sr{sub 0.76}Bi{sub 0.24}O){sub 1.74}CrO{sub 2}, and Bi{sub 0.44}(Sr{sub 0.7}Bi{sub 0.3}O){sub 1.88}CrO{sub 2}--has been synthesized and characterized, using electron microscopy and powder X-ray diffraction. Two sets of reflections are evidenced in the ED patterns, associated to the coexistence of two monoclinic S{sub 1} and S{sub 2} subsystems, with [100]{sup *} and [001]{sup *} as common axes and a parameter misfit along [010]{sup *}: S1 {l_brace}a, b{sub 1}, c, {beta}{r_brace} with a {approx} 5 {angstrom}, b{sub 1} {approx} 5 {angstrom}, c {approx} 29.8 {angstrom}, and {beta} {approx} 93{degree} and S{sub 2} {l_brace}a, b{sub 2}, c, {beta}{r_brace} with a {approx} {angstrom}, b{sub 2} {approx} 2.9 {angstrom}, c {approx} 29.8 {angstrom}, and {beta} {approx} 93{degree}. High-resolution electron microscopy showed that it is the first misfit layered oxides involving double rock salt-type (RS) layers, i.e., triple (AO)-type layers (A = Ca and Sr), with a single (H) hexagonal (CoO{sub 2}) or (CrO{sub 2}) layer. As a result, these oxides can be described as the members n = 3/m = 1 of a large family with the general formula Bi{sub {alpha}}(A{sub 0.75{+-}{var_epsilon}}Bi{sub 0.25{+-}{var_epsilon}}O){sub (n+nx)/2}(MO{sub 2}){sub m}. In those structures, the bismuth cations are supposed to be distributed over two sorts of sites: (i) the A-sites, filling partly the RS layers and (ii) the sites located between the RS and the H layers, ensuring the cohesion of the structure. The {chi}(T) measurements show a paramagnetic behavior above 100 K and are in agreement with a mixed valence Co{sup 2+} (high spin) and Co{sup 3+} (low spin) for all the cobalt oxides. They confirm the presence of Cr{sup 2+} (high spin) in the chromium phases and evidence strong antiferromagnetic interactions at low temperature and paramagnetism with a Curie-Weiss law above 100 K. The Cr oxides are insulators, whereas the pure Bi-cobalt phases are semiconductors or dirty metal when the samples have been lead doped.
- OSTI ID:
- 329181
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 142; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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