Micro-structure analysis in Mn, Ba-doped (K,Na)NbO<sub>3</sub>-based lead-free piezoelectric ceramic

The structures of the main component (K,Na)NbO3 (KNN) in a lead-free piezoelectric ceramic 0.97[(K0.48Na0.52)0.82Ca0.04Li0.02Nb0.85O3−δ]–0.03[K0.85Ti0.85Nb1.15O5]–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 kp = 0.42, dielectric constant ε33T/ε0 = 750, and mechanical quality factor Qm = 650.