Carbon combustion synthesis of nanostructured perovskites

Abstract

A novel, economical, and energy-efficient process to produce nanostructured particles of several perovskite oxides, such as ferroelectrics BaTiO3, SrTiO3 and LiNbO3, is described. This process, referred to as carbon combustion synthesis of oxides (CCSO) is a modified SHS process that uses carbon as a fuel instead of a pure metal. In CCSO of nanostructured materials, the exothermic oxidation of carbon nanoparticles (∼5 nm) with a surface area of 80 m2/g generates a thermal reaction wave with temperature of up to 1200°C that propagates through the solid submicron reactant mixture, converting it to the desired complex oxide product. The carbon is not incorporated in the solid product since it is released in a gaseous form (CO2) from the sample. The quenching front method combined with XRD and Raman spectroscopy revealed that crystalline tetragonal BaTiO3 particles formed in the early stage of the combustion, before the temperature reached its maximum. A major difference between the thermal transport processes during CCSO and conventional SHS is the extensive emission of CO2. The release of CO2 enables synthesis of highly porous (up to 70%) powders having a particle size in the range of 60–80 nm with a surface area of up to 12.4 m2/g.