Effect of preparation methodologies on the electrical properties of lead-free 0.985(K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3-0.015(Bi0.5Na0.5)ZrO3 piezoceramics

Abstract

Two methods of preparation namely, one-step solid state method and two-step solid state method, were used to synthesize composite 0.985(K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3-0.015(Bi0.5Na0.5)ZrO3 (0.985KNNLS-0.015BNZ) piezoceramics. In one-step method, all the raw materials were mixed in their stoichiometric ratios and then calcined to yield the desired composite. In two-step method, calcined samples of (K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3 (KNNLS) and (Bi0.5Na0.5)ZrO3 (BNZ) were initially prepared following the above procedure, these calcined powders were mixed according to the required compositional ratios and then again calcined to get the final composite. The calcined powders were again high-energy ball-milled in isopropanol medium at the speed of 250 rpm for 10 h. The powders were pressed into pellets and sintered at 1060 °C for 2 h. According to XRD analysis and Raman spectra, both the resulting ceramic samples show pure perovskite structure. The study reveals the great influence of the preparation technique on the microstructural, electrical and pieozoelectric properties of the resulting ceramics. Significantly higher value of Curie temperature Tc = 331 °C was observed for ceramics prepared via two-step method as compared to Tc = 197 °C for ceramics synthesized via one-step method. Modified Curie Weiss law and Vogel-fulcher relation suggest that two-step approach induces more relaxor character in the sample. The values of piezoelectric coefficient (d33 = 367 pC/N), remnant polarization (Pr = 13µC/cm2) and dielectric permittivity (εrt = 2166) corresponding to the two-step method far exceed those (d33 = 253 pC/N, Pr = 6.65 µC/cm2, εrt =1428) of the one-step method. These observed results are discussed in this paper.