Lead-free piezoelectric ceramics in the (1 - x)Sr2NaNb5O15-xCa2NaNb5O15 (0.05 ≤ x ≤ 0.35) system

The electrical properties of dense lead-free piezoelectric ceramics in the Sr2-xCaxNaNb5O15 (SCNN) system with x ranging from 0.05 to 0.35 is reported. XRD patterns all showed a single tetragonal tungsten bronze phase, peak broadening being seen on increasing the Ca content. The lattice constant calculation indicated distortion and shrinkage of the crystal structure with Ca substitution. Dielectric spectra of each composition displayed two dielectric anomalies and diffusive phase transitions. The Curie temperature, Tc, shifted upward, whereas the dielectric constant at Tc declined monotonically as the Ca content increased. The ferroelectric and piezoelectric properties of SCNN largely depended on the Ca content. The composition with x = 0.15 showed the greatest polarisation with Pr = 3.0 microCoulomb/cm2 and piezoelectric constant of d33 = 96 pC/N, whereas the compositions with x = 0.30 and 0.35 almost lost their ferroelectricity and piezoelectricity. The results appear to show that lead-free SCNN piezoelectric ceramics are of interest for electromechanical applications. 25 refs.