New low temperature multiphase ferroelectric films

Abstract

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.

Low-Temperature Solution Approaches for the Potential Integration of Ferroelectric Oxide Films in Flexible Electronics

“…Whereas the crystallization of the ferroelectric phase mainly occurs well above 500C, intermediate nonferroelectric oxides, like pyrochlore or fluorite-type phases, are just stable below this temperature. [1,37,89] Therefore, low temperature treatments of solution derived layers usually lead to films in which an incipient ferroelectric phase is immersed in an amorphous matrix that contains organic residuals and second phases. As a result, the ferroelectric response of these films is spoiled.…”

“…This concept is very close to the ferrons model reported by the group of Prof. Mackenzie early this century. [89] Although ferroelectric response of these nanocomposite BZNT films is low (P R  3 µC cm -2 ) ( Fig. 1), they are easily prepared on flexible substrates with low degradation temperatures and have interest in appealing areas today like flexible energy storage applications.…”

Pulsed-laser deposited amorphous-like PZT thin-films: Microstructure and optical properties

“…4,12 Amorphous alloys and glasses are typically fabricated using melt-quenching technique, 2,3,10 or like often in the case of thin films, mostly by spin coating sol-gel liquids. 5,11 Although XRD analysis of these materials reveals them to be in amorphous state, there are some features in these processes that should be considered from the materials structure point of view. In melt-quenching process, materials are heated up to high temperatures over the melting temperature, and then rapidly cooled down to form an amorphous solid.…”

“…Only it is important that the entity fundamentally responsible of ferroelectricity in the matter, like distorted BO 6 oxygen octahedra in the case of ferroelectric perovskite ABO 3 compounds, still exists, no matter how distorted, but still in an identifiable form. This assumption was further developed to consider chemical bonds, such as Ba-Ti-O, formed in organic solutions used to fabricate gelderived glasses in the form of thin films at temperatures as low as 200 • C. 11 The ferroelectric response was found to be due to existence of so-called "ferrons", arranged entities of the size in the scale of around ∼50 Å composed of TiO 6 octahedrals, visible also in transmission electron microscopy (TEM) micrographs. Although the existence of ferroelectricity in the films was clearly proved, other properties of the films, including optical transmittance T(), refractive index n, remanent polarization P r , dielectric constant ε, and loss angle tan δ, were found to be controlled mainly by the organic residuals or pores still present in the films.…”

Network Connectivity and Crystallization in the Transparent Ferroelectric Nanocomposite LaBGeO5

“…Many different compositions (e.g., LiNbO 3 , BaTiO 3 ) can produce glass-ceramics that are transparent with ferroelectric crystallites. 1,2 However, many of these compositions produce multiple distinct crystalline phases upon devitrification, complicating their characterization and analysis. The apparently simple crystallization behavior of LaBGeO 5 has made it the target of many investigations.…”