Macroporous Monoliths of Functional Perovskite Materials through Assisted Metathesis

Solid-state reactions between metal sulfates and metal oxides (assisted by K 2 CO 3 ) have been used to prepare two classes of important perovskite materials: ferroelectric PbTiO 3 and the catalyst/magnetic/fuel-cell material La 1 - x Sr x MnO 3 ( x = 0.0 and 0.3). K 2 CO 3 helps to drive the reaction by forming highly stable K 2 SO 4 and CO 2 . Performing the reactions within solid monoliths and then dissolving out K 2 SO 4 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 μm. 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.