Periodic configuration of δ-boundaries and ferroelectric domains in Li-modified (K, Na)NbO3 lead-free piezoelectric single crystals by solid state crystal growth

(K0.45Na0.55)0.94Li0.06NbO3 (KNLN) lead-free piezoelectric single crystals have been prepared by solid-state crystal growth (SSCG) method using faceted KTaO3 single crystals as a seed. SEM-EBSD, PFM and TEM investigations revealed a specific periodic configuration of δ-boundaries and ferroelectric domains in the KNLN single crystal. The single crystal is sliced into several nearly parallel segments by δ-boundaries and each segment has a mean thickness of 2-3 μm. Neighboring segments show a misorientation of 1.4°/[1232] while the alternate segments have the same orientation. The two segments exhibit different ferroelectric domain structures: periodic (100) domain walls and (11¯l) domain walls, respectively. The periodic (100) domain wall pattern can be sketched by tetragonal 180° or orthorhombic 90° domains. The as-observed periodic configuration of small-angle δ-boundaries and ferroelectric domains could be related to the specific stress fields in the epitaxial crystal growth embedded in a ceramic matrix.