Two New Rb3Sc(IO3)6 Polytypes in Proposed Nonlinear Optical Family A3M(IO3)6 (A = K, Rb; M = Sc, In): Topology–Symmetry Analysis, Order–Disorder and Structure–Properties Relation

Two polytypic modifications of new non-centrosymmetric iodate Rb3Sc(IO3)6 are synthesized hydrothermally. Their structures demonstrate different degrees ordering and solved in the same space group, Pc, with differing choice b-axis: either 20 or 40 Å is selected from diffraction data, measured on crystals better ordering. The difference NLO properties two polytypes disclosed. Topology–symmetry analysis separated blocks layers allowed determination local symmetry corresponding to mirror plane m, which defines strong optical nonlinearity. Layer alternation indicates a nature Rb, Sc-iodate its similarity K, In- Sc-nonlinear-optical crystals, group Fdd2, belonging proposed common family A3M(IO3)6 (A = Rb; M Sc, In), whose explained basis for every known member. Hypothetical structural variant predicted; disorder crystal growth conditions discussed as factors affecting properties.