Large-Sized (K, Na)NbO3-based piezoelectric Single Crystals doped with Ba2+ ions: Seed-Free Solid-State growth, Structure, and properties

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.