Phase structure and enhanced piezoelectric properties of lead-free ceramics (1-x)(K 0.48Na 0.52)NbO 3-(x/5.15) K 2.9Li 1.95Nb 5.15O 15.3 with high curie temperature

Lead-free (1-x)(K 0.48Na 0.52)NbO 3-(x/5.15) K 2.9Li 1.95Nb 5.15O 15.3 (KNN-KLN100x, x=0-0.25) piezoelectric ceramics have been prepared by a conventional solid-state sintering technique. The effects of potassium lithium niobate (KLN) content on the phase structure and piezoelectric properties were investigated. The addition of KLN markedly increased the paraelectric cubic-ferroelectric tetragonal phase transition temperature (T C), but greatly shifted the polymorphic phase transition from the ferroelectric orthorhombic to the ferroelectric tetragonal phase (T O-T) to near room temperature. At room temperature, coexistence of the orthorhombic and tetragonal phases was identified at approximately 0.12≤X≤0.18 by the analysis of X-ray diffraction patterns and dielectric spectroscopy, which led to a significant enhancement of the piezoelectric properties. The ceramics with x=0.16 exhibited excellent piezoelectric properties: piezoelectric constant d 33=235 pC/N, planar electromechanical coupling factor k p=41.6%, and Curie temperature T C=473°C. Moreover, they also have an excellent thermal stability in the severe aging test up close to their Curie temperatures. These results indicated that the KNN-KLN100x ceramics are very promising lead-free piezoelectric candidates, especially for high-temperature applications. © 2011 The American Ceramic Society.