Multiphase design induced improved electrical response in BNZ modified (K0.485Na0.485Li0.03)(Nb0.96Sb0.04)O3 piezoceramics with high Curie temperature

A detailed investigation of structural, electrical and piezoelectric properties has been performed on lead-free piezoelectric ceramics (1 − x)(K_0.485Na_0.485Li_0.03)(Nb_0.96Sb_0.04)O₃-x(Bi_0.5Na_0.5)ZrO₃ [(1 − x)KNNLS-xBNZ], synthesized by traditional solid-state sintering technique. The Rietveld refinement of the XRD patterns confirms the coexistence of rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) phases near room temperature. Temperature-dependent dielectric study reveals that an optimum amount of BNZ in KNNLS can shift the phase transition temperature (T_R–O) towards room temperature and improve the piezoelectric properties of (1 − x)KNNLS-xBNZ ceramics. For BNZ content of x = 0.015, the (1 − x)KNNLS-xBNZ ceramic exhibits enormous increase in its (i) room temperature dielectric constant ε_r by 250% with a simultaneous decrease in the dielectric loss tanδ, and (ii) remnant polarization P_r by 120% with a favorable decrease in the coercivity E_c, from their corresponding values observed for x = 0. This composition also shows enhanced piezoelectric properties with piezoelectric charge coefficient d₃₃ = 326 pC/N, and electromechanical coupling factor k_p = 39%, and an appreciably higher Curie temperature T_c of 335 °C. The improved properties of the composition have been explained on the basis of various features such as crystallite size, lattice strain, grain size, and favorable phase structure of the evolved ceramic system consequent upon addition of BNZ. The study demonstrates that an optimum addition of BNZ in KNNLS can greatly enhance the dielectric, ferroelectric and piezoelectric properties along with the Curie temperature which can widen the scope of using this system in various industrial applications.