LiNbTeO₅: A High-Performance Multifunctional Crystal Material with a Very Large Second-Harmonic Generation Response and Piezoelectric Coefficient

It is an urgent and challenging task to explore mid-infrared (mid-IR) nonlinear optical (NLO) crystals with excellent comprehensive performances. Herein, the first alkaline-metal niobium tellurite crystal LiNbTeO5 with outstanding mid-IR NLO and piezoelectric properties was synthesized by simple 1:1 fusion of LiNbO3 and TeO2. Its structure featured two types of second-order Jahn–Teller distortive units, namely, octahedral-coordination NbO6 and (TeO3)2– groups with stereoactive lone pairs as well as a rare LiO5 polyhedron. Its second-harmonic generation (SHG) effect was extremely strong (17 × KDP at 1064 nm and 2.3 × KTP at 2.09 μm), with one of the largest values among all reported Te-containing metal oxides. In addition, LiNbTeO5 exhibited other advantages over LiNbO3, including the widest IR transparent window (0.33–9.0 μm) among all reported Te-containing metal oxide NLO crystals, a higher laser damage threshold (LDT, 460 MW·cm–2), and a larger piezoelectric coefficient (d33 = 18 pC·N–1). Benefiting from its good growth habit and physicochemical properties, centimeter-sized crystals and high-quality devices were obtained. This work provided a promising NLO and piezoelectric multifunctional crystal, and the simple yet effective strategy was inspirational.