MgNb₂ O₆ Modified K_0.5 Na_0.5 NbO₃ Eco-Piezoceramics: Scalable Processing, Structural Distortion and Complex Impedance...

In this work, piezoceramics of the lead-free composition K_0.5 Na_0.5 NbO₃ with an increasing amount of MgNb₂ O₆ (0, 0.5, 1, 2 wt.%) were prepared through conventional solid-state synthesis and sintered in air atmosphere at 1100 °C. The effect of magnesium niobate addition on structure, microstructure and piezoelectric properties was evaluated. The ceramics maintain the orthorhombic Amm2 phase for all compositions, while an orthorhombic Pbcm secondary phase was found for increasing the concentration of MgNb₂ O₆ . Our results show that densification of these ceramics can be significantly improved up to 94.9 % of theoretical density by adding a small amount of magnesium-based oxide (1 wt.%). Scanning electron microscopy morphology of the 1 wt.% system reveals a well-packed structure with homogeneous grain size of ∼2.72 μm. Dielectric and piezoelectric properties become optimal for 0.5-1.0 wt.% of MgNb₂ O₆ that shows, with respect to the unmodified composition, either higher piezoelectric coefficients, lower anisotropy and relatively low piezoelectric losses (d₃₃ =97 pC N^-1 ; d₃₁ =-36.99 pC N^-1 and g₃₁ =-14.04×10^-3  mV N^-1 ; Q_p (d₃₁ )=76 and Q_p (g₃₁ )=69) or enhanced electromechanical coupling factors (k_p =29.06 % and k₃₁ =17.25 %).