Bismuth layer-structured ferroelectrics

An alternative structure that has also been widely investigated both for high temperature piezoelectric, as well as for ferroelectric memory applications is the bismuth layer structure family as shown in Figure 1.14 for SrBi2Ta209 (sbt), e.g. [8], The structure consists of perovskite layers of different thicknesses, separated by Bi20 + layers. It has been shown that when the perovskite block is an even number of octahedra thick, the symmetry imposes a restriction on the polarization direction, confining it to the a-b plane. In contrast, when the perovskite block is an odd number of octahedra thick, it is possible to develop a component of the polarization along the c axis (nearly perpendicular to the layers). This could be used in... 

Kato K., Suzuki K., Fu D., Nishizawa K., Mild T. Chemical approach using tailored liquid sources for traditional and novel ferroelectric thin films. Jpn. J. Appl. Phys. 2002a 41 6829-6835 Kato K., Suzuki K., Nishizawa K., Miki T. Ferroelectric properties of alkoxy-derived CaBi4Ti40is thin films on Pt-Passivated Si. Appl. Phys. Lett. 2001 78 1119-1121 Kato K., Suzuki K., Fu D., Nishizawa K., Miki T. Platinum-assisted phase transition in bismuth-based layer-structured ferroelectric CaBi4Ti40i5 thin films. Appl. Phys. Lett. 2002b 81 3227-3229 Nishizawa K., Mild T., Suzuki K., Kato K. Control of crystallization and crystal orientation of alkoxy-derived SrBi2Ta209thin films by ultraviolet irradiation. J. Mater. Res. 2003 18 899-907 Sanchez C., Livage J., Henry M., Babonneau F. Chemical modification of alkoxide precursors. J. Non-Cryst. Solids 1988 100 65-76... 

The phase transiton from a paraelectric to a ferroelectric state, most characteristic for the SbSI type compounds, has been extensively studied for SbSI, because of its importance with respect to the physical properties of this compound (e.g., J53, 173-177, 184, 257). The first-order transition is accompanied by a small shift of the atomic parameters and loss of the center of symmetry, and is most probably of a displacement nature. The true structure of Sb4S5Cl2 106), Bi4S5Cl2 194), and SbTel 108,403) is still unknown. In contrast to the sulfides and selenides of bismuth, BiTeBr 108) and BiTel (JOS, 390) exhibit a layer structure similar to that of the Cdl2 structure, if the difference between Te, Br, and I (see Fig. 36) is ignored. 

High-quality, pore-free microstructures of PZ - PT piezoceramic, (b) and (c), are essential for reliable, high-performance applications, e.g. composites and arrays where very small elements are cut from larger pieces (e.g. see Fig. 6.36) (d) the layer-structured bismuth titanate ferroelectric (Bi4Ti3012) Tc 650°C the crystal structure consists of perovskite layers separated by bismuth oxide layers) is exploited in high-temperature applications, including accelerometers and flow-meters (reproduced with permission of Ferroperm Piezoceramics A/S, Denmark). 

Lu, C.H., Wu, C.H. Preparation, sintering, and ferroelectric properties of layer-structured strontium bismuth titanatium oxide ceramics. J. Eur. Ceram. Soc. 22, 707-714 (2002)... 

As mentioned before, the bismuth layered perovskite structure BLnT exhibits strong structural anisotropy, which results in strong crystallographic orientation dependence of ferroelectric properties. Many studies indicate that c-axis-oriented (001) epitaxial BLaT, BNdT thin films exhibit a very low remanent polarization along the film normal, because the vector of the spontaneous polarization in the layered perovskite materials is almost along a axis. Therefore, it is of interest to know whether there is similar orientation dependence of PL properties of BEuT thin films [53]. 

Perovskite-related Oxides.—The perovskite-related oxides have been studied extensively in recent years because of the large variety of device applications for which these materials are suited. The interaction between structure, properties, and stoicheiometry is significant at all levels, but here we will discuss only the narrow areas where intergrowth is a dominant structural feature. We will not, therefore, consider solid solutions typified by the Pb(Zr Tii )03 ferroelectrics, and neither will we discuss the structurally complex but stoicheiometric phases related to hexagonal BaTiOj, which includes BaNiOj, which has a simple two-layer repeat in the c-direc-tion, the nine layer BaRuOj, the twelve layer Ba4Re2CoOj2, and the twenty-four layer Sr5Re20ig phase. The crystal chemistry of these phases is treated in detail by Muller and Roy. The materials we shall discuss are the two series of phases A B 0 +2 and A + B 02n+, and the bismuth titanates. Some of the anion deficient perovskites, ABO -x, will be considered in Section 5. 

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