Growth, domain dynamics and piezoelectric properties of some lead-free ferroelectric crystals

Lead-free solid solution crystals (Na, Bi)TiO₃–BaTiO₃ [NBBT] and (K,Na)NbO₃–LiNbO₃[KNN–LN] have been grown by the Bridgman method. Their piezoelectric constant d₃₃ reach 160 and 405 pC/N, respectively. Domain dynamics shown through in-situ observation using a polarizing microscopy in 0.94NBT-0.06BT crystals demonstrate that both of ferroelectric–antiferroelectric phase transition and antiferroelectric–paraelectric one take place in broad temperature ranges. 0.94NBT-0.06BT is more relaxor ferroelectric whereas 0.95KNN-0.05LN crystal is more normal ferroelectric. Moreover, it is found that the ferroelectric phase coexists with the paraelectric phase at the temperature much higher than their Curie temperature in both crystals. The low value of d ₃₃ may originate from the existence of an antiferroelectric tetragonal phase in a ferroelectric rhombohedral phase in NBBT crystals.