Alignment of Λ-Shaped Basic Building Units to Construct One New KMoO3(IO3) 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 KMoO3(IO3), i.e., δ-KMoO3(IO3), to understand the effect of different packing patterns of basic building units on structures and properties. Among four polymorphs of KMoO3(IO3), the different stacking patterns of Λ-shaped cis-MoO4(IO3)2 units result in α- and β-KMoO3(IO3) featuring nonpolar layered structures, whereas γ- and δ-KMoO3(IO3) display polar frameworks. Theoretical calculations and structure analysis reveal that IO3 units can be regarded as the main source of its polarization in δ-KMoO3(IO3). Further property measurements show that δ-KMoO3(IO3) 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.