Solution decomposition of the layered double hydroxide of Co with Fe: phase segregation of normal and inverse spinels

Abstract

The nitrate-intercalated layered double hydroxide of Co with Fe decomposes on hydrothermal treatment to yield an oxide residue at a temperature as low as 180 °C. The oxide product is phase segregated into a Co₃O₄-type normal spinel and a CoFe₂O₄-type inverse spinel. Phase segregation is facilitated as decomposition in a solution medium takes place by dissolution of the precursor hydroxide followed by reprecipitation of the oxide phases. In contrast, thermal decomposition takes place at 400 °C. This temperature is inadequate to induce diffusion in the solid state whereby phase segregation into the thermodynamically stable individual spinels is suppressed. The result is a single-phase metastable mixed spinel oxide. This is rather uncommon in that a hydrothermal treatment yields thermodynamically stable products where as thermal decomposition yields a metastable product.