Small Changes, Big Impact: Tungsten Bronzes with Extremely Large Second Harmonic Generation Achieved by the Transition Metal Doping on the B‐Site
Yejin Pi, Yunseung Kuk, Kang Min Ok
Abstract
Abstract Two novel transition metal‐doped tungsten bronze oxides, Pb 2.15 Li 0.85 Nb 4.85 Ti 0.15 O 15 (PLNT) and Pb 2.15 Li 0.55 Nb 4.85 W 0.15 O 15 (PLNW), are synthesized by high‐temperature solid‐state reactions. The Rietveld method using the high‐resolution synchrotron radiation indicates that PLNT and PLNW crystallize in the orthorhombic polar noncentrosymmetric space group, Pmn 2 1 (no. 31). As a class of tungsten bronze oxide, PLNT and PLNW retain a unique rigid framework composed of d 0 transition metal cation (Ti 4+ or W 6+ )‐doped highly distorted NbO 6 octahedra along with the subsequently generated Pb/LiO 12 and PbO 15 polyhedra. Interestingly, the d 0 transition metal‐doped tungsten bronzes, PLNT and PLNW, exhibit extremely large second‐harmonic generation (SHG) responses of 56 and 67 × KH 2 PO 4 , respectively. The observed immeasurably strong SHG is mainly attributed to a net polarization originating from the alignment of highly distorted NbO 6 octahedra with doped transition metals in the frameworks. It is believed that doping transition metal cations at the B‐site of the tungsten bronze structures should be an innovative strategy to develop novel high‐performance nonlinear optical materials.