New low temperature multiphase ferroelectric films

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This article describes the low-temperature synthesis of new multiphase ferroelectrics containing an inorganic ferroelectric phase entrapped in amorphous silica or in an organically modified silicate (ormosil). Sol gel derived LiNbO3 and BaTiO3 crystals were grown in SiO2 and in RSiO1.5 glass where R contains a chromophore (TDP) insensitive to hydrolysis and condensation reactions. The LiNbO3–SiO2 and BaTiO3–SiO2 compositions as well as the TDP–LiNbO3–SiO2 and TDP–BaTiO3–SiO2 ormosils exhibit ferroelectric-like properties. This unusual characteristic is due to the presence of small, partially ordered crystallites of the ferroelectric, dispersed in the amorphous matrix. In addition to their ferroelectric properties, the ormosils also exhibit interesting optical characteristics: the TDP–BaTiO3–SiO2 materials are red, whereas the TDP–LiNbO3–SiO2 are yellow. The materials described in this article are representative of two new classes of weak ferroelectrics. In the first class, a ferroelectric is dispersed in an amorphous matrix. The second class may be called “organically-modified crystals”: small ferroelectric crystals embedded in an organically modified matrix. The fabrication of such materials is possible for inorganic crystalline phases forming at temperatures below the decomposition temperature of the organic (about 250 °C). This article also contains some theoretical considerations explaining why these materials, although amorphous by x-ray diffraction, exhibit ferroelectric-like properties.