Effect of vanadium substitution on electrical and piezoelectric properties of lead-free (K0.5Na0.5)NbO3 ceramics

Abstract

During the last decade, efforts have been made towards developing lead-free piezoelectric ceramics which can replace the currently dominant but highly superior lead-based piezoelectric materials such as PZT. (K0.5Na0.5)NbO3-based piezoelectrics are one promising candidate because of their relatively high Curie temperatures and piezoelectric coefficients. In the present work, powders of (K0.5Na0.5)(Nb1−x V x )O3 (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) were synthesized by conventional solid state reaction of K2CO3, Na2CO3, Nb2O5, and V2O5. The powders were high-energy milled in isopropyl alcohol medium using a Retsch PM 100 planetary ball mill at the speed of 200 rpm for 8 h. The milled powders were sintered at 1080 °C for 1 h in closed alumina crucible. The crystalline phase of the ceramics was found to be perovskite with orthorhombic symmetry. Increasing V5+ content in the ceramics from x = 0 to x = 0.03 gives rise to gradual increase in room temperature dielectric constant (e r ) from 346 to 432, remnant polarization (P r ) from 6.2 to 9.6 μC/cm2, electromechanical coupling factor (k p ) from 0.35 to 0.39, and piezoelectric charge constant (d 33) from 76 to 93 pC/N. The increase in these parameters is attributed to the associated increase in density of the ceramics with increasing V5+ content. Further increase in V5+ content to x = 0.05 results in decrease in e r , P r , k p and d 33 to 390, 4.7 μC/cm2, 0.33 and 67 pC/N respectively. The study reveals that an optimum concentration of V5+ can enhance the dielectric, ferroelectric and piezoelectric properties of (K0.5Na0.5)NbO3 system.