Chemical synthesis of calcium stannates from peroxo precursors

A chemical route for the low-temperature synthesis of the calcium stannates CaSnO3 and Ca2SnO4, potential materials for dielectric applications, is reported. Mixed cation precursor powders, derived using calcium chloride, tin tetrachloride and hydrogen peroxide, were calcined at relatively low temperatures of about 700–1200 °C to form homogeneous crystalline CaSnO3 and Ca2SnO4. The structural evolution of the crystalline phases was studied using X-ray diffraction, differential thermal analysis, thermogravimetric analysis, scanning electron microscopy, Brunauer-Emmett-Teller measurements and chemical analysis. The thermal degradation of the X-ray amorphous peroxo precursors to the single-phase stannates occurs in two steps for the formation of CaSnO3 and in three steps for the formation of Ca2SnO4. CaSnO3 is one of the intermediate products formed during the thermal decomposition to Ca2SnO4. The ultrafine powders resulting after the thermal degradation of the precursors have a small impurity content. They show a high sinterability at temperatures above 1000 °C which increases from Ca2SnO4 to CaSnO3. The highests densities reached for ceramic samples were about 97% of the theoretical value for CaSnO3 and 95% for Ca2SnO4 by sintering at 1400 °C for 4 h.