Abstract
B-site substitution in KNN with tantalum results in a higher d33 and dielectric constant. This higher value makes KNNT interesting for lead-free actuator applications. KNNT fibers with diameters of 300 and 500 μm have been extruded and sintered at 1200 °C in a KNNT-enriched atmosphere. Subsequently, the influence of fiber diameter on the microstructure (porosity and grain size) was investigated. The measurements revealed that with decreasing fiber diameter, the porosity increases, whereas the grain size decreases. The influence of these microstructural differences on the piezoelectric properties was evaluated using a novel characterization procedure for single fibers. The larger diameter fibers show an increase in the electromechanical properties measured, i.e., d33, tanδ, Pr, Ec and the free longitudinal fiber displacement, when compared to smaller diameter fibers. The lower alkali losses result in a larger grain size, a higher density during sintering and lead to higher electromechanical properties.
Highlights
Potassium sodium niobate is an environmentally-friendly alternative to lead-based piezoelectric ceramics and could eventually play a comparable role as lead zirconate titanate (PZT) in certain electronic applications in the future, with the added advantage of being bio-compatible [1,2,3]
Optimal ferroelectric properties are exhibited by materials with a large grain size and low porosity, which applies to PZT [19], barium titanate [20,21], KNN [22,23], etc
Comparing the grain size results with earlier studied bulk samples [24], the grain size of the fibers is slightly higher than bulk disc samples
Summary
Potassium sodium niobate is an environmentally-friendly alternative to lead-based piezoelectric ceramics and could eventually play a comparable role as lead zirconate titanate (PZT) in certain electronic applications in the future, with the added advantage of being bio-compatible [1,2,3]. The properties making Ta substitution interesting for actuator applications are the enhancement of the dielectric and piezoelectric properties [9] It has a similar valance, ionic radius and similar electro-negativity to niobium (Ta, 1.5; Nb, 1.6) [10]. These properties make Ta an ideal candidate to act as a B-site substituent in KNN, as shown by Lee et al, who produced (K0.47Na0.545)(Nb0.55Ta0.45)O3 (KNNT) powder. The influence of fiber diameter on the microstructure properties (porosity, grain size, elemental stoichiometry, etc.) and the small and large signal electromechanical properties, such as piezoelectric charge coefficient (d33), polarization evolution (P-E) loop and strain evolution (S-E) loop, were investigated. The reported results for the large signal response (i.e., S-E and P-E loops) and the small signal response (i.e., d33, tanδ and er) are the averages of five fibers with the standard deviation calculated from these
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