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Confined synthesis of metastable complex oxides

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Confinement - the key to stabilisation in crystal structures

There is a high demand for new materials with appealing multifunctional properties for information and communication technologies as memory or sensor devices. EU research has delivered some interesting new products.

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As properties of inorganic solids are intimately linked to their crystal structures, the COSYMETCOX (Confined synthesis of metastable complex oxides) project used a novel approach to extend the properties and applications of metastable complex oxides. Using matrix confinement, they stabilised metastable phases to produce nanoscale polymorphs. The researchers also identified and investigated the basic properties of the stabilising mechanism. They worked with magnetoelectric systems relevant to the research – epsilon iron (III) oxide (ε-Fe2O3) and a new phase of La0.7Sr0.3MnO3. The latter displays an elevated Curie temperature when magnetic properties are lost. As the matrix confined method is not always suitable for these nano-oxides, the scientists addressed this limitation. Integration of these oxides requires complete control of their microstructure as well as precise positioning in a technologically appropriate substrate. COSYMETCOX success included a robust method to prepare ε-Fe2O3 films on strontium titanate substrate. They discovered that this metastable polymorph is ferroelectric at room temperature. This is the first reporting of a multiferroic single metal oxide as it is acknowledged that it is also ferroelectric at ambient temperatures. Confined synthesis of the monoclinic La0.7Sr0.3MnO3 in silica matrices gave surprise results. After thermal treatment of the gels, the researchers discovered a substantial amount of α-quartz, not manganite as expected. The researchers also started investigation of the crystallisation of new metastable phases under negative pressures in liquids. The work will continue in the research portfolio of some project members after COSYMETCOX finishes.

Keywords

Confinement, stabilisation, crystal structures, metastable, magnetoelectric

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