Piezoelectric properties of SrBi 4 Ti 4 O 15 ferroelectric ceramics
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The dynamic piezoelectric response of SrBi4Ti4O15 ceramics with Aurivillius structure was investigated at high alternating stress, low frequencies (0.01 to 100 Hz), and temperatures from 20 to 200 °C. The piezoelectric nonlinearity, observed only at high pressures (>10 MPa) and elevated temperatures (>150 °C), is interpreted in terms of contributions from non-180° domain walls. At weak fields, the frequency dependence of the longitudinal piezoelectric coefficient was explained in terms of Maxwell–Wagner piezoelectric relaxation. The Maxwell–Wagner units are identified as colonies that consist of highly anisotropic grains which sinter together, and whose distribution in the ceramic is strongly dependent on sintering conditions.
I. INTRODUCTION
Many compositions that belong to the family of bismuth titanate (Bi4Ti3O12or BIT) based materials possess a high transition temperature and have been considered for use in high-temperature piezoelectric applications.1 These materials have recently also attracted considerable attention for potential applications in nonvolatile ferroelectric memories due to their excellent polarization fatigue resistance.2 Finally, following the current interest in developing lead-free piezoelectric components, bismuth titanate based materials may be of interest as an alternative to conventional lead-based compositions for certain applications. The crystal structure of these compositions, first described by Aurivillius,3 is characterized by pseudoperovskite layers (A m−1 BO 3m+1 stacked between + (Bi2O2)2 layers.4 A is a mono, divalent or trivalent cation and B a quadri, penta, or hexavalent metal. The number of perovskite layers is represented by m. Due to the layer structure, the compositions exhibit a very high anisotropy of properties.5 With the known exception of monoclinic BIT, in most Aurivillius phases the structure can be described as orthorhombic below the paraelectric– ferroelectric phase transition temperature, and polarization takes place in the ab plane.6,7 The piezoelectric effect is also highest in this plane. In the ceramics, the microstructure of such materials consists of platelikeshaped grains.8 For these crystallites, the smallest dimension of the grain corresponds to the crystallographic c axis so that the polarization lies in the plane of the grains. From the point of view of piezoelectric properties, SrBi4Ti4O15 (SBTO15) is of special interest because of its high Curie temperature (≈530 °C) and its remarkably stable properties with respect to the driving field 1376
http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 6, Jun 2002 Downloaded: 16 Mar 2015
amplitude and frequency.9,10 This stability has been discussed using crystallographic arguments by Reaney and Damjanovic.11 They presented evidence that the ferroelastic and ferroelectric phase transitions in SBTO15 do not occur at the same temperature, as in BaTiO3 and PbTiO3. On cooling, SBTO15 first undergoes a phase transition from a high-temperature tetragonal paraelectric-paraelastic phase into an orthorhom
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