Macroporous monoliths of functional perovskite materials through assisted metathesis

Solid-state reactions between metal sulfates and metal oxides (assisted by K2CO3) have been used to prepare two classes of important perovskite materials: ferroelectric PbTiO3 and the catalyst/magnetic/fuel-cell material La1-xSrxMnO3 (x = 0.0 and 0.3). K2CO3 helps to drive the reaction by forming highly stable K2SO4 and CO2. Performing the reactions within solid monoliths and then dissolving out K2SO4 crystals in water permit macroporous materials to be obtained. The monoliths possess connected, open porosity with characteristic pore sizes of the order of 5-30 mum. Imprinted on this macroporous structure is a second, smaller scale of porosity arising from the sintering together of particles with sizes in the 100-300-nm range. The reaction pathways have been followed by thermodiffractometry, and the products characterized by Rietveld refinement of powder X-ray diffraction patterns, by scanning electron microscopy, and by dc magnetization measurements.