New low temperature multiphase ferroelectric films

This article describes the low-temperature synthesis of new multiphase ferr oelectrics containing an inorganic ferroelectric phase entrapped in amorpho us 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 re actions. The LiNbO3-SiO2 and BaTiO3-SiO2 compositions as well as the TDP-Li NbO3-SiO2 and TDP-BaTiO3-SiO2 ormosils exhibit ferroelectric-like propertie s. This unusual characteristic is due to the presence of small, partially o rdered 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 ar ticle are representative of two new classes of weak ferroelectrics. In the first class, a ferroelectric is dispersed in an amorphous matrix. The secon d class may be called "organically-modified crystals": small ferroelectric crystals embedded in an organically modified matrix. The fabrication of suc h materials is possible for inorganic crystalline phases forming at tempera tures below the decomposition temperature of the organic (about 250 degrees C). This article also contains some theoretical considerations explaining w hy these materials, although amorphous by x-ray diffraction, exhibit ferroe lectric-like properties. (C) 2001 American Institute of Physics.