MS-12-P-2216 A TEM study of Bi0.5Na0.5TiO3-based ceramics
Ferroelectric materials and especially PZT-based ceramics are frequently used in electronic devices such as actuators, transducers, sensors [1]. Due to recent environmental regulations [2] there is a strong push to replace lead (Pb) in these materials. One such system that is currently considered as a potential replacement for PZT is Bi0.5Na0.5TiO3 (BNT). The challenge in searching for lead-free ceramics is a lack in the fundamental understanding of structure-property relationship in these materials.
In the present work transmission electron microscopy (TEM) has been employed to investigate a series of BNT-based solid solutions. Fig. 1 shows the bright-field image of ferroelectric domains of a ternary system 0.9(Na0.5Bi0.5)TiO3-0.05(Bi0.5K0.5)TiO3-0.05BaTiO3 (BNT-BKT-BT). The domain pattern was recorded close to [001] zone axis at room temperature. The main crystallographic directions are given, according to the corresponding SAED pattern of the same area shown in Fig. 2. A parallel band like configuration of the ferroelectric domains can be observed. In the SAED pattern 1/2 ooe (where “o” and “e” stand for odd and even hkl indexes, respectively) reflections are observed besides the fundamental perovskite reflections, indicating the presence of in-phase oxygen octahedral tilting [3, 4] (a0a0c+, in Glazer notation [5]). The diffuse electron scattering has also been characterized by using rotation electron diffraction (RED) method [6]. This way we can achieve a better understanding of the short-range structural order/disorder of the material using the 3D information in reciprocal space. When tilting the crystal to higher zone axes the diffuse scattering becomes clearly visible as shown in Fig. 3. However, besides the fundamental perovskite reflections we can observe 1/2 ooo superstructure reflections indicating most likely a-a-a- anti-phase octahedral tilting.
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[5] A. M. Glazer, Acta Cryst. B28, 3384 (1972)
[6] W. Wan, J. Sun, J. Su, S. Hovmöller and X. Zou, J. Appl. Crystallogr.46, 1863-1873 (2013)
Acknowledgement: The Kunt and Alice Wallenberg Foundation is acknowledged for supporting the electron microscopy facilities and the project “3D Electron Microscopy for Nanostructure Research”(3DEM-NATUR).
Fig. 1: Bright field transmission electron microscopy image of the ferroelectric domains viewed close to [001]pc |
Fig. 2: SAED pattern along a <001>pc zone axis. Pseudo-cubic (PC) system was used to index the pattern |
Fig. 3: SAED pattern along a <114>pc zone axis displaying diffuse electron scattering along {04-1}*pc. Pseudo-cubic (PC) system was used to index the pattern |
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