Innovative Process Development of Sr 2 (Nb 0.5 Ta 0.5 )O 7 /PVDF Hybrid Materials for Sensors and Actuators
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HYBRID MATERIALS
FOR
W. Kowbel, V. Chellappa, and J.C. Withers, MER Corp., Tucson, AZ and M.J. Crocker, Mechanical Engineering, Auburn University, Auburn, AL and B. Wada, JPL, Pasadena, CA ABSTRACT Over the past several years interest in adaptive 'smart'materials development Smart structures utilize both polymeric sensors and has gained momentum. lead-based piezo-ceramic actuators. This paper addresses the development of an alternative smart material which consists of a novel lead-free piezoceramic/PVDF hybrid composite, to be used as a single component system capable A lead-free controlled porosity perovskite of performing multiple tasks. ceramic of the type A2B20 7 (Sr 2 (Nb 5 Ta. 5) 207 was developed utilizing hot forging. Long, oriented grains along the x-y plane, perpendicular to the forging direction were obtained in the ceramics. PVDF was subsequently infiltrated into the porous piezo-ceramic resulting in a three dimensional architecture in which the piezo-ceramic is oriented perpendicular to the PVDF. It is anticipated that manufacturability combined with the ease of functional tailorability of such a class of lead-free hybrid materials can be useful in a variety of smart structures applications. INTRODUCTION Over the past several years, piezoelectric ceramic/polymer composites have been extensively investigated in order to get improved piezo- and pyroelectric properties [1]. Several methods are employed to make these composites including injection molding (2], dice and fill [3] and reticulation [4]. These materials are designed so that the high piezoelectric coefficients and low dielectric constants of bulk ceramics are combined with low density and good flexibility of the polymers. This paper reports the fabrication of novel Sr 2 (Nb. 5Ta. 5 ) 20 7 /PVDF composites. The hot-forged Sr 2 (Nb. 5 Ta. 5 ) 20 7 (SNTO) ceramic is lead-free and was previously reported to exhibit high which can be adjusted by controlling the content of Ta [5].
Curie temperature
EXPERfMENTAL Figure 1 shows the fabrication flow chart for Sr2(Nb. 5 Ta. 5 ) 20 7 /PVDF composites. Initially, appropriate amounts of SrCO3 , Nb205 and Ta 2O5 powders were mixed with a 3% binder and an appropriate amount of a polystyrene pore-former. Subsequently, the ceramic powders were cold pressed at 1.4 MPa into rectangular composites. The green bodies were sintered at 1250 0 C and then hot-forged at 14000 C. The porous ceramic material was subsequently infiltrated with the PVDF solution and poled using the conventional DC poling method at 20 kV/cm. Density of the resulting composites was measured using the Archimedes principle. SEM was used to analyze the microstructure, while XRD was used to perform the phase identification and determine the degree of the preferred orientation by the calculation of the orientation factor. The frequency spectra was obtained using an impedance analyzer and the electromechanical properties were determined by the resonance method.
65 Mat. Res. Soc. Symp. Proc. Vol. 459 1997 Materials Research Society
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