Lead-free vanadium-substituted (K_0.485Na_0.5Li_0.015)(Nb_0.9Ta_0.1)O₃ piezoceramics synthesized from nanopowders

Lead-free, alkaline niobate-based piezoelectric ceramics substituted with vanadium (K_0.485Na_0.5Li_0.015)(Nb_0.9−x Ta_0.1V _x )O₃ (x = 0, 0.05, 0.10, 0.15 and 0.2) were synthesized from nanocrystalline powders by traditional solid state sintering technique. The base composition chosen is among those recently reported to show high piezoelectric properties. The nanocrystalline powders were produced by high energy ball milling. The crystalline phase of all the ceramics prepared was found to be perovskite with orthorhombic symmetry. Without any sintering aid, the bulk density of 97 % of the theoretical density was obtained for the ceramics with no vanadium. The optimum sintering temperature for all compositions was achieved at a low value of 1,050 °C. In the composition range studied, increasing V⁵⁺ content in the ceramics gives rise to a gradual decrease in room temperature dielectric constant (ε _r ) from 1,193 to 474, remnant polarization (P _r ) from 12.9 to 5.6 μC/cm², electromechanical coupling factor (k _p ) from 0.45 to 0.32, and piezoelectric charge constant (d ₃₃) from 156 to 53 pC/N. The decrease in these parameters is attributed to the associated decrease in density and grain size of the ceramics with increasing V⁵⁺ content. Increasing V⁵⁺ content from 0 to 0.15 results in an increase in the coercive field from 9.9 to 15.5 kV/cm, thereby, making the ceramics harder in this range of composition.