First evidence of a phase transition in a high-pressure metal iodate: Structural and thermal studies of AgIO3 polymorphs

Article abstract of DOI:10.1002/ejic.201300191

A new phase of silver iodate, β-AgIO₃, was obtained at 2.7 GPa by heating the α-AgIO₃ precursor above 240 °C. β-AgIO₃ is the first iodate obtained at high pressure that stabilizes under normal conditions. The crystal structure was determined by X-ray powder diffraction and Rietveld refinement. In comparison to α-AgIO₃, which crystallizes in the Pbc2₁ acentric orthorhombic space group with the lattice parameters a = 7.265(2) A, b = 15.17(4) A, c = 5.786(2) A, and V = 638(2) A³, β-AgIO₃ crystallizes in the Pbca centric orthorhombic space group, with the following parameters: a = 6.137(2) A, b = 16.980(4) A, c = 5.827(1) A, and V = 607.3(3) A³. Differential thermal analysis under high pressure (2.7 GPa) and structural studies showed an endothermic transformation at 260°C corresponding to a first-order reconstructive phase transition from α-AgIO₃ to β-AgIO₃. The thermal behaviors of α-AgIO₃ and β-AgIO₃ were studied by differential scanning calorimetry at ambient pressure and in situ temperature-dependent X-ray powder diffraction. Copyright