Molten salt synthesis of up to 100 μm Ni_(0.5)Zn_(0.5)Fe_2O_4 platelets

摘要

Size controlled (5 to 100 μm) Ni_(0.5)Zn_(0.5)Fe_2O_4 ferrite platelets have been obtained by a reaction in a molten salt between hematite platelets, NiO and ZnO powders. Whereas hematite starting platelets are single crystals, the reaction with nickel and zinc oxides yield the formation of polycrystalline platelets whose initial shape and size are conserved. SEM observations reveal the presence of adjacent micronic ferrite crystals with their [111] faces parallel to the platelet surface. Increasing the reaction temperature promotes an enlargement of the [111] faces. KCl as a flux give better results than NaCl with, at a same temperature, no modification of the crystal shape and no ZnO loss. A topotactic reaction is proposed as a mechanism allowing the platelet morphology to be conserved. Its parameters are controlled by the respective solubilities of oxides and ferrites in the corresponding KCl and NaCl molten salts.