First Evidence of a Phase Transition in a High‐Pressure Metal Iodate: Structural and Thermal Studies of AgIO3 Polymorphs. Issue 20 (31st May 2013) - Suffren, Yan
Abstract: 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 Pbc 21 acentric orthorhombic space group with the lattice parameters a = 7.265(2) Å, b = 15.17(4) Å, c = 5.786(2) Å, and V = 638(2) Å 3, β ‐ AgIO3 crystallizes in the Pbca centric orthorhombic space group, with the following parameters: a = 6.137(2) Å, b = 16.980(4) Å, c = 5.827(1) Å, and V = 607.3(3) Å 3 . 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. Abstract : β ‐ AgIO3 is the first iodate phase obtained under high pressure. The reconstructive phase transition from the α ‐ AgIO3 acentric phase to the dense β ‐ AgIO3 centric phase is an endothermic transformation that occurs at 260 °C at 2.7 GPa.