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Transparent single crystals of a new iodate Cs5[Sc2(IO3)9](IO3)2 were synthesized under mild hydrothermal conditions. X-ray diffraction of single crystal was used to determine the large crystal structure with 52 independent atoms, sp. gr. P21/c. The building blocks [Sc(IO3)6]3− of Sc octahedra and six (IO3) groups are condensed into a framework; the structure contains additional isolated (IO3) groups. Large Cs cations occupy holes and form an intercrossing framework. Similar building blocks [M(IO3)6] are known for many iodates; however, most are isolated. Their topology and symmetry differ and determine the properties of the compounds. [ABSTRACT FROM AUTHOR]

New polar iodate Cs3Ta(IO3)8, space group P31c, has been obtained under mild hydrothermal conditions and its structural determination was carried out with a single crystal. Two types of layers were selected and characterized using topology and symmetry analysis. The structure of the new iodate has relation with KSc(IO3)3Cl determined earlier. The polar space group corresponds to the presence of the distinct effect of optical second harmonic generation, but the SHG intensity is limited due to lack of phase matching for neodymium laser radiation and its second harmonic. The low optical nonlinearity is consistent with the structural feature of the crystal, and the polarity is determined mainly by the positions of Cs cations with a slight deviation from the centrosymmetry of the entire structure as a whole. Two structural variants of Cs3Ta(IO3)8 are predicted based on a OD topology-symmetry approach. [ABSTRACT FROM AUTHOR]

The influence of mole fraction and nature of the cations in positions [8]A and [6]B of the pyrochlores containing Na+, Ca2+, Cd2+, U4+, Nb5+, Ta5+, Ti4+, Sb5+, Zr4+, V3+, V4+, W5+, W6+ synthesized under hydrothermal conditions at 800 °C, 200 MPa and controlled oxygen fugacity in NaF solution of 1.0 mol·kg−1 H2O on lattice parameters has been considered. The unit cell parameters of the fluorpyrochlores where for Nb5+ or Ta5+ were substituted by other cations showing distinct linear variations from the effective cations radii in positions [8]A and [6]B. Based on the literary data analysis, the two-parameter nonlinear equation describing dependence of pyrochlore lattice parameters on the cation radii for the oxide-pyrochlores has been proposed. [ABSTRACT FROM AUTHOR]