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Preparation of La0.67Ca0.33MnO3 Nano-Phase Powders and Films from Alkoxide Precursors
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry.
2002 In: Chem. Mater., Vol. 14, 1981-1988 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2002. Vol. 14, 1981-1988 p.
URN: urn:nbn:se:uu:diva-91284OAI: oai:DiVA.org:uu-91284DiVA: diva2:163967
Available from: 2004-01-21 Created: 2004-01-21Bibliographically approved
In thesis
1. Sol−Gel Synthesis of CMR Manganites
Open this publication in new window or tab >>Sol−Gel Synthesis of CMR Manganites
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The development of more advanced materials forms the basis of technological progress. One group of fascinating compounds with many potential applications in spintronic devices are the mixed-valence perovskite manganites. These have attracted considerable interest during the last decade through their very large magnetoresistance near the Curie Temperature. Although the properties of a material determinie any application, the development of reliable and flexible synthesis methods is crucial, as is the understanding of these methods. Knowledge of how different materials are formed is also of general importance in tailoring new materials. The aim of this project has therefore been not only to develop a new synthesis route, but also to understand the mechanisms involved.

This thesis describes the synthesis and characterization of a novel manganese alkoxide and its use in sol–gel processing of magnetoresistive perovskite manganites. In searching for a soluble manganese alkoxide for sol–gel processing, we found that the methoxy-ethoxide, [Mn19O12(moe)14(moeH)10]·moeH, has a high solubility in appropriate organic solvents. Being 1.65 nm across, it is one of the largest alkoxides reported; it is also of interest because of its (for oxo-alkoxides) rare planar structure. After mixing with La, Nd, Ca, Sr, and Ba methoxy-ethoxides, [Mn19O12(moe)14(moeH)10]·moeH was used in the first purely alkoxide based sol–gel processing of perovskites manganites. The phase evolution on heating xerogel powders to 1000°C was studied, and thin films were prepared by spin-coating.

It was found that the easily oxidised Mn-alkoxide facilitates the formation of high oxygen-excess modifications of the perovskites. The reactive precursor system yields fully hydrolysed gels almost without organic residues, but the gel absorbs CO2 from the air, leading to carbonate formation. The carbonate decomposition is the limiting step in oxide formation. Transport measurements of La0.67Ca0.33MnO3 films on LaAlO3 substrate show that all-alkoxide sol–gel derived films can compete with PLD films in terms of quality of epitaxy and transport. The somewhat different behaviour of the sol–gel derived films compared to PLD films is attributed to differences in morphology and oxygen stoichiometry.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 50 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 929
Inorganic chemistry, sol-gel, alkoxide, doped manganites, CMR, perovskite, phase development, Oorganisk kemi
National Category
Inorganic Chemistry
urn:nbn:se:uu:diva-3970 (URN)91-554-5855-6 (ISBN)
Public defence
2004-02-13, Häggsalen, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 14:00
Available from: 2004-01-21 Created: 2004-01-21Bibliographically approved

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