Alignment of Λ-Shaped Basic Building Units to Construct One New KMoO 3 (IO 3 ) Polar Polymorph.

Nonlinear optical (NLO) crystals assume an irreplaceable role in the development of laser science and technologies, yet the reasonable design of a high-performance NLO crystal remains difficult owing to the unpredictability of inorganic structures. In this research, we report the fourth polymorph of KMoO 3 (IO 3 ), i.e., δ-KMoO 3 (IO 3 ), to understand the effect of different packing patterns of basic building units on structures and properties. Among four polymorphs of KMoO 3 (IO 3 ), the different stacking patterns of Λ-shaped cis -MoO 4 (IO 3 ) 2 units result in α- and β-KMoO 3 (IO 3 ) featuring nonpolar layered structures, whereas γ- and δ-KMoO 3 (IO 3 ) display polar frameworks. Theoretical calculations and structure analysis reveal that IO 3 units can be regarded as the main source of its polarization in δ-KMoO 3 (IO 3 ). Further property measurements show that δ-KMoO 3 (IO 3 ) exhibits a large second-harmonic generation response (6.6 × KDP), a wide band gap (3.34 eV), and a broad mid-infrared transparency region (∼10 μm), which demonstrates that adjusting the arrangement of the Λ-shaped basic building units is an effective approach for rationally designing NLO crystals.