Fabrication and Electrical Characterization of Translucent Bi12TiO20 Ceramics

The production of high-density Bi12TiO20 ceramics, their transmission spectrum, and impedance features are reported. The samples were synthesized at 700°C/6？h and sintered at 800°C/3？h. This procedure yielded translucent ceramics with relative density of % and average grain size of ？μm. Samples with 0.5？mm thickness were translucent with optical transmission of about 30% at 800？nm. The electrical and dielectric properties of the high-density ceramics were studied and compared with those measured for samples with lower density and also with the literature about Bi12TiO20 single crystals. The activation energy for the conduction process in high-density ceramic was 0.99？eV, and the dielectric permittivity was 40 at 200°C. These values are comparable to those reported for single crystals. 1. Introduction Bismuth titanate (Bi12TiO20—BTO) crystallizes in a body-centered cubic structure with I23 space group and two chemical formulas per unit cell. It belongs to a class of materials known as sillenites [1], which includes the isomorphs Bi12SiO20, BSO, and Bi12GeO20, BGO. These crystals have many interesting properties, including electrooptical and photoconductive ones [2–4]. The combination of these properties causes the so-called photorefractive effect that consists of a reversible light-induced change in the refractive index [4]. These features render sillenite-type crystals useful in a variety of advanced and potentially promising applications such as reversible recording media for real-time holography or image processing applications [2]. In comparison to BSO and BGO, BTO presents some practical advantages for technological applications, including a higher electrooptic coefficient and smaller optical activity [5, 6]. Transparency of photoconductive materials is a desirable feature since the photons must be transported efficiently to the absorption centers of the bulk material. In recent years, many efforts have been made to improve the transparency of polycrystalline materials aiming at the substitution of single crystals for several applications [7–10]. These works suggest that high density (low porosity) is necessary for transparency since the pores are very efficient scattering centers. Besides the optical quality, the electrical and dielectric properties of photoconductive polycrystals must be studied as well, so as to provide a better understanding of their electrical behavior and achieve the optimization of their properties. A material’s conductivity depends on its overall characteristics, such as its chemical composition, purity, and microstructure.