Evidence of reaction intermediates in microwave-assisted synthesis of SHG active α-La(IO3)3 nanocrystals

Abstract

We explore here how, under microwave assisted hydrothermal process, various synthesis conditions influence the formation of different lanthanum iodate compounds: α-La(IO₃)₃, La(IO₃)₃(H₂O), La(IO₃)₃(HIO₃) and La(IO₃)_2.66(OH)_0.66. Whatever the initial [La³⁺] : [IO₃⁻] ratio, α-La(IO₃)₃ crystallizes if the synthesis temperature exceeds 220 °C. Phase transformations in solid state or under hydrothermal synthesis are also discussed. Interestingly, we evidence the full phase transformation under hydrothermal synthesis from the new hydrate form La(IO₃)₃(H₂O) into stable and optically active α-La(IO₃)₃ through an appropriate hydrothermal process. This evolution can be explained by structural rearrangements of the coordination sphere of lanthanum atoms, stabilizing the structure.