Multifunctional Sm³⁺ modified layered perovskite La₂Ti₂O₇ single crystals: Enhanced piezoelectric performance and color-stable orange emission

The demand for multifunctional materials with optical and electrical properties in industrial high-temperature applications has witnessed a rapid upsurge. Among ultra-high Curie temperature perovskite-like layered structure piezoelectrics, La₂Ti₂O₇ (LTO) single crystal possesses the highest piezoelectric coefficient, but the lack of luminescence limits its optical applications. In this work, by combining experiments and first-principles calculations, we find that Sm³⁺ doped LTO single crystals not only create strong orange emission with high-color-purity and high-color-stability under high temperature/pressure, but also achieve higher piezoelectric coefficient of 21.7 pC/N at 298 K and 25.6 pC/N at 773 K, accompanied by polarization enhancement originating from inner TiO₆ octahedral twisting. In addition, systematic high-temperature in situ electrical measurements showed that Sm³⁺ doping also contributes to weakening the adverse effects of ferroelectric-ferroelectric phase transition on piezoelectricity, dielectricity, and conductivity. Our work provides insights into the performance optimization mechanisms of ultra-high Curie temperature piezoelectrics and paves the way for the development of high-performance electro-optic integrated and coupled devices for applications under extreme conditions.