Crystal chemistry of some addition compounds of alkali iodates with telluric acid

Five addition compounds of telluric acid with alkali iodates are described. Three of these compounds are orthorhombic and isotypic: RbIO3·Te(OH)6, KIO3·Te(OH)6, and NH4IO3·Te(OH)6. The crystal structure of this class of compounds has been solved with the potassium salt whose unit-cell dimensions are a = 14.30(1) Å, b = 6.734(5) Å, c = 8.711(5) Å, Pc21n (C92v). Z = 4. Crystal data are given for the two isotypic salts. The crystal structures of two other compounds have been determined. 2KIO3·Te(OH)6 is trigonal, R3̄, with the unit cell dimensions a = 6.500(5) Å, c = 25.717(8) Å, Z = 3 for the hexagonal description. NH4IO3·Te(OH)6·H2O is triclinic (P1̄) with a = 10.99(1) Å, b = 6.932(4) Å, c = 6.559(4) Å, α = 88.89(5), β = 90.88(5), γ = 104.48(5)°, and Z = 2. For these three different crystal structure determinations the final R values are, respectively, 0.047, 0.030, and 0.036. The first class of compounds described in this paper, MIO3·Te(OH)6 (M = K, Rb, NH4) is a new class of piezoelectric materials.