Micro-structure analysis in Mn, Ba-doped (K,Na)NbO₃-based lead-free piezoelectric ceramic

Abstract

The structures of the main component (K,Na)NbO₃ (KNN) in a lead-free piezoelectric ceramic 0.97[(K_0.48Na_0.52)_0.82Ca_0.04Li_0.02Nb_0.85O_3−δ]–0.03[K_0.85Ti_0.85Nb_1.15O₅]–x[MnO₂, BaCO₃] (x = 0.00, 0.01, 0.015, 0.02, and 0.03) have been investigated with synchrotron powder X-ray diffraction and transmission electron microscopy measurements. The structural symmetry of the KNN phase has shown the P4mm in the X-ray diffraction data of all samples from x = 0.00 to 0.03. The Mn-rich clusters of 10–50 nm size in KNN phase have been observed by energy dispersive X-ray spectroscopy element mapping images at x = 0.02. The Mn-rich clusters with the same crystal structure as KNN are dispersed in the KNN matrix with rotational relationship of the coincidence site lattice Σ = 5. The x = 0.02 sample has shown the high piezoelectric properties of piezoelectric constant d₃₃ = 140 pC/N, electromechanical coupling coefficient k_p = 0.42, dielectric constant ε₃₃^T/ε₀ = 750, and mechanical quality factor Q_m = 650.