Enhanced electric field induced strain in SrTiO3 modified (K,Na)NbO3-based piezoceramics

• (100−x)KNNLT – xST ceramics were prepared and their properties were studied.
• 92.5KNNLT-7.5ST showed maximum dynamic piezoelectric constant (d33∗=400pm/V).
• Its reason is electric field-induced transition from nonpolar to polar phase.
• 99KNNLT-1ST showed maximum piezoelectric constant (d33 = 208 pC/N).
• Its reason is coexistence of orthorhombic and tetragonal symmetries.

Lead-free 0.96K0.5Na0.5NbO3–0.04LiTaO3 ceramics modified with different amounts of SrTiO3 (ST) from zero to 10 mol% were prepared by normal sintering. It was found that ST modification changed the crystal structure from orthorhombic to tetragonal and for ceramics with 10 mol% ST, pseudocubic structure was formed which was nonpolar. Investigation of bipolar strain revealed that with increasing ST content to 7.5 mol%, the negative strain decreased. This observation was attributed to the existence of nonpolar regions with local composition close to that of the ceramic containing 10 mol% ST. This phenomenon was accompanied with strain enhancement in unipolar strain curve because of the contribution of strain due to electric field-induced transition from nonpolar to ferroelectric phase, in addition to electric field induced strain.