Practical Electron Microscopy and Database

BaTiO₃ (barium titanate) was one of the first commercially viable ferroelectric materials [6]. Because of this, it has also been one of the most comprehensively studied ferroelectrics with a simple and well-known structure. [7]

In Table 2312a, the fundamental part of the cubic BaTiO₃ lattice cell for ferroelectric and piezoelectric properties is represented by the TiO₆ octahedron, with Ti⁴⁺ ion in the center. The lattice stability is ensured by the Ba²⁺ ions at the corners of the unit cell.

Table 2312a. Properties of BaTiO₃.

Tsuda et al. [8] suggested that the phase transformations in BaTiO₃ ferroelectric crystals have an order-disorder character, namely only the rhombohedral phase has an ordered structure but the orthorhombic and tetragonal phases have disordered structures. Moreover, Tsuda et al. [10] were able to observe the two-dimensional (2D) distribution of the small atomic displacements  (~10 pm) cased by the ferroelectric polarization in the rhombohedral phase of the tetragonal BaTiO₃ nanostructures using the CBED method in STEM mode. However, Shibata et al. [9] observed the polarizations in BaTiO₃ tetragonal phase using atomic resolution differential phase-contrast (DPC) imaging based on the aberration-corrected STEM.

The transition temperatures of BaTiO₃ are given by,

BaTiO₃ has three ferroelectric phases and three Curie temperatures as shown in Table 2312b.

Table 2312b. Characteristics of BaTiO₃.

Figure 2312a shows the temperature-composition phase diagram of (Ba_1-xSr_x)TiO₃.

In EELS, perovskite type ferroelectric and high-k dielectric materials, such as BaTiO₃ and SrTiO₃, normally show only one interband plasmon peak [1–4].

The EDS profile of BaTiO₃ system shown in Figure 2312b presents an example of EDS peak overlap. However, the FWHM of the WDS peaks is only a few eV because the energy resolution of the wavelength spectrometer is 5-10 eV. In this case, peak overlap in WDS is not a problem.

Figure 2312c shows an example of Curie temperature T_c as a function of the grain size. Here, T_c represents the temperature of the tetragonal–cubic phase transition.

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[10] Kenji Tsuda, Akira Yasuhara, and Michiyoshi Tanaka, Two-dimensional mapping of polarizations of rhombohedral nanostructures in the tetragonal phase of BaTiO3 by the combined use of the scanning transmission electron microscopy and convergent-beam electron diffraction methods, Applied Physics Letters, 103, 082908 (2013).