Large-sized (K, Na)NbO3-based piezoelectric single crystals doped with Ba2⁺ ions: seed-free solid-state growth, structure, and properties

Abstract High-performance lead-free piezoelectric single crystals are critical for next-generation transducers and sensors. In this work, (1- x )(K, Na, Li)(Nb, Bi, Fe)O 3 - x BaCO 3 [(1- x )(KNLNBF)- x Ba] piezoelectric single crystals (0 ≤ x ≤ 0.009) were synthesized through a seed-free solid-state crystal growth (SFSSCG) method. Ba 2+ incorporation enhances lattice compatibility and accelerates crystal growth, yielding a maximum crystal size of 20×18×2 mm 3 at x = 0.005 for the (1- x )(KNLNBF)- x Ba crystals. The Rietveld refinement indicates that the introduction of Ba 2+ leads to an increase in the tolerance factor ( t = 1.016) through A-site substitution (\(\:{r}_{{Ba}^{2+}}\) = 1.61 Å). The (1- x )(KNLNBF)- x Ba crystal doped with Ba 2+ ions at x = 0.005 obtains optimal overall properties: d 33 = 367 pC/N, d 33 ∗ = 793 pm/V, P r = 36.1 µC/cm 2 , k t = 0.433, T C = 415°C, T O−T = 143°C, and tanδ = 0.019. This work indicates that introducing Ba 2+ ions into the KNLNBF system can provide a route for regulating and improving the properties of piezoelectric crystals.