Synthesis and Characterization of Two New Second Harmonic Generation Active Iodates: K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl

Transparent single crystals of two new iodates K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl have been synthesized hydrothermally. Single-crystal X-ray diffraction was used to determine their crystal structures. Both compounds crystallize in non-centrosymmetric space groups. The compound K₃Sc(IO₃)₆ crystallizes in the orthorhombic space group Fdd2. The crystal structure is made up of [ScO₆] octahedra, [IO₃] trigonal pyramids, and [KO₈] distorted cubes. The compound KSc(IO₃)₃Cl crystallizes in the trigonal space group R3. The building blocks are [ScO₆] octahedra, [KO₁₂] polyhedra, and [IO₃] trigonal pyramids. The Cl^- ions act as counter ions and reside in tunnels in the crystal structure. The second harmonic generation (SHG) measurements at room temperature, using 1064 nm radiation, on polycrystalline samples show that the SHG intensities of K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl are around 2.8 and 2.5 times that of KH₂PO₄ (KDP), respectively. In addition, K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl are phase-matchable at the fundamental wavelength of 1064 nm. The large anharmonicity in the optical response of both compounds is further supported by an anomalous temperature dependence of optical phonon frequencies as well as their enlarged intensities in Raman scattering. The latter corresponds to a very large electronic polarizability.