Piezoelectric properties of SrBi 4 Ti 4 O 15 ferroelectric ceramics Marlyse Demartin Maeder, Dragan Damjanovic, Cyril Voisard, and Nava Setter Ceramics Laboratory, Materials Department, Swiss Federal Institute of Technology - EPEL, 1015 Lausanne, Switzerland (Received 21 June 2001; accepted 14 March 2002) The dynamic piezoelectric response of SrBi 4 Ti 4 O 15 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 bis- muth titanate (Bi 4 Ti 3 O 12 or 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 ferro- electric memories due to their excellent polarization fa- tigue resistance. 2 Finally, following the current interest in developing lead-free piezoelectric components, bismuth titanate based materials may be of interest as an alterna- tive to conventional lead-based compositions for certain applications. The crystal structure of these compositions, first de- scribed by Aurivillius, 3 is characterized by pseudo- perovskite layers (A m-1 BO 3 m+1 stacked between (Bi 2 O 2 ) 2 + layers. 4 A is a mono, divalent or trivalent cat- ion and B a quadri, penta, or hexavalent metal. The num- ber of perovskite layers is represented by m. Due to the layer structure, the compositions exhibit a very high an- isotropy 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 polari- zation 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 platelike- shaped grains. 8 For these crystallites, the smallest dimen- sion 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, SrBi 4 Ti 4 O 15 (SBTO15) is of special interest because of its high Curie temperature (≈530 °C) and its remark- ably stable properties with respect to the driving field amplitude and frequency. 9,10 This stability has been dis- cussed using crystallographic arguments by Reaney and Damjanovic. 11 They presented evidence that the ferro- elastic and ferroelectric phase transitions in SBTO15 do not occur at the same temperature, as in BaTiO 3 and PbTiO 3 . On cooling, SBTO15 first undergoes a phase transition from a high-temperature tetragonal paraelec- tric-paraelastic phase into an orthorhombic(I) para- electric–ferroelastic phase. Observations of electron dif- fraction patterns by transmission electron microscopy re- veal the presence of superlattice reflections associated with this phase transition. 11 Suppelattice reflections are observed below 650–680 °C, suggesting that the phase transition occurs in this temperature range. 11 At this phase transition only ferroelastic non-180° domain walls are created. On further cooling, SBTO15 transforms at 530 °C from the orthorhombic(I) paraelectric– ferroelastic phase into as orthorombhic(II) ferro- electric–ferroelastic phase. At this phase transition, only ferroelectric 180° domain walls are created within al- ready existing ferroelastic domains structure. A similar intermediate paraelectric phase has recently been de- scribed in related Sr 0.85 Bi 2.1 Ta 2 O 9 composition by Her- voches et al. 12 Another possible evidence of a high temperature nonferroelectric phase transition in Aurvil- lius structures has been reported by Jimenez et al. 13 where an elastic anomaly was observed above the tem- perature of the paraelectric–ferroelectric phase transition. Those authors, however, interpreted the elastic anomaly to be of extrinsic and not structural origin. Because 180° domain walls (associated with the fer- roelectric spontaneous polarization) and non-180° do- main walls (associated with the ferroelastic spontaneous strain) are created at different temperatures and under different boundary conditions, and because 180° domain J. Mater. Res., Vol. 17, No. 6, Jun 2002 © 2002 Materials Research Society 1376 https://doi.org/10.1557/JMR.2002.0205 Downloaded from https:/www.cambridge.org/core. 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