Analysis of crystallographic evolution in (Na,K)NbO3-based lead-free piezoceramics by x-ray diffraction

The crystallographic structure of (Na,K)NbO3-based compounds and phase transitional behavior in (1−x)(K0.5Na0.5)NbO3–xLiNbO3 (x=0, 3, 6, and 8mol%) ceramics were accurately determined using high resolution x-ray diffraction (XRD). The phase transition between orthorhombic and tetragonal was distinctly characterized focusing on the XRD peak changes in {222} and {400} diffraction planes, by which lattice parameters of the perovskite type subcell, a, b, and c as well as angle β can be calculated. The discontinuous change in angle β at x=6mol% is located at the phase transitional region, where enhanced piezoelectric constant d33=215pC∕N was obtained. The present study provides a precise as well as simple method to investigate crystallographic structures in (Na,K)NbO3-based ceramics.