Sm³⁺ Doping Enables Ultrahigh Piezoelectricity and Electrooptic Activity in PMN-PT Single Crystals

Relaxor ferroelectric crystals are cornerstone materials for electromechanical and electro-optic technologies, yet the antagonism between piezoelectric performance and optical transparency has persistently impeded device integration. Here, we demonstrate that Sm³⁺ doping in Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) single crystals shatters this conventional compromise, achieving an exceptional piezoelectric coefficient (d₃₃ = 3500 pC/N) by [001]-poling and a large electro-optic coefficient (γ_c = 700 pm/V) by [110]-poling while retaining >70% optical transmittance across the visible-near-infrared spectrum. Through multiscale structural analysis, we unveil that Sm³⁺ incorporation induces lattice contraction and catalyzes the formation of polar nanoregions (PNRs), leading to a polymorphic nanodomain architecture (20-200 nm) that facilitates low-energy polarization rotation and minimizes domain wall pinning. Notably, [110] crystallographic poling is identified as the optimal configuration for balancing an enhanced piezoelectric response (d₃₃ = 1600 pC/N) with superior optical clarity. These crystals concurrently maintain practical thermal stability (T_RT > 70 °C) and mechanical quality factors (Q_m ≈ 105). Our work establishes rare-earth doping as a universal materials-design strategy for engineering multifunctional ferroelectrics that transcend traditional property limitations.