Doped and Undoped BaTiO3
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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.

Crystal structure
Perovskite/Cubic Orthorhombic Rhombohedral Perovskite/Tetragonal Body-centered tetragonal Hexagonal
Lattice parameters (Å)
a = 3.988 a = 3.99, b = 5.669, and c = 5.682   a = 3.9998 and c = 4.018    
Space group
Pm-3m (221) Amm2 (38) R3m (160) P4mm (99) I4/mcm (140) P63/mmc (194)
Positions
Ba (1a): (0, 0, 0), Ti (1b): (1/2, 1/2, 1/2), O (3c): (1/2, 1/2, 0) Ba (2a): (0, 0, 0), Ti (2b): (1/2, 0, 0.51), O1 (2a): (0, 0, 0.49), and O2 (4c): (1/2, 0.253, 0.237) Ba(1a): (0, 0, 0), Ti(1a): (1/2+xTi, 1/2+xTi, 1/2+xTi), O(3b): (1/2+xO, 1/2+xO, zO) Ba (1a): (0, 0, 0), Ti (1b): (1/2, 1/2, 1/2+zTi), O1 (1b): (1/2, 1/2, zbO), O2 (2c): (1/2, 0, 1/2+zcO) Ti(2c): (0, 0, 0), Sr(2b): (0, 0.5, 0.25), O(2a): (0, 0, 0.25), O(4h): (−u+0.5, u, 0)  
Temperature
> 393 K 275 K > T > 185 K < 185 K Room temperature    

Bulk modulus B (GPa)

185          
Cohesive energy (eV)
29.9          
Band gap (eV)
3.7          
Ferroelectric polarization (μC/cm2)
  ~20 ~20 ~20    
Application
Ferroelectric
Ferroelectric
Ferroelectric
Ferroelectric
Polar axis of ferroelectric phases
[001]
[011]
[111]

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,

393 K
275 K
185 K
 
 

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

Table 2312b. Characteristics of BaTiO3.

Structure type Rhombohedral
Tc
-90 °C


-90 °C
Orthorhombic
Tc
5 °C


5 °C
Tetragonal
Tc
120 °C


120 °C
Cubic
1460 °C


1460 °C
Hexagonal
Space group R3m (160) Amm2 (38) P4mm (99) Pm-3m P63/mmc (194)
Property Ferroelectric Ferroelectric Ferroelectric Non-polar Non-polar

Figure 2312a shows the temperature-composition phase diagram of (Ba1-xSrx)TiO3.

Temperature-composition phase diagram of (Ba1-xSrx)TiO3

Figure 2312a. Temperature-composition phase diagram of (Ba1-xSrx)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.

EDS and WDS profiles of BaTiO3

Figure 2312b. EDS and WDS profiles of BaTiO3. The green spectrum presents a standard EDS of of BaTiO3, while the red one presents a standard WDS. EDS shows the overlapped Ba Lα-Ti Kα and Ba Lβ1-Ti Kβ peaks.

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

Tc in BaTiO3 as a function of the grain size

Figure 2312c. Theoretical Tc in BaTiO3 as a function of the grain size. Adapted from [5]

 

 

 

[1] K.S. Katti, M. Qian, F. Dogan, M. Sarikaya, J. Am. Ceram. Soc. 85 (2002) 2236–2243.
[2] K. van Benthem, C. Elsasser, R.H. French, J. Appl. Phys. 90 (2001) 6156–6164.
[3] S. Schamm, G. Zanchi, Ultramicroscopy 88 (2001) 211–217.
[4] J. Zhang, A. Visinoiu, F. Heyroth, F. Syrowatka, M. Alexe, D. Hesse, H.S. Leipner, Phys. Rev. B 71 (2005) 064108.
[5] P. Perriat, J.C. Niepce, G. Caboche: J. Thermal Anal. 41, 635–649 (1994).
[6] B. Jaffe, Piezoelectric ceramics, (Academic Press, London, 1971).
[7] G. H. Haertling, Journal of the American Ceramic Society, 82, 4 (1999).
[8] K. Tsuda, R. Sano, and M. Tanaka, Phys. Rev. B 86, 214106 (2012).
[9] N. Shibata, S. D. Findlay, Y. Kohno, H. Sawada, Y. Kondo, and Y. Ikuhara, Nat. Phys. 8, 611–615 (2012).
[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).

 

 

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