THERMAL-ANALYSIS AS AN AID IN THE SYNTHESIS OF NONSTOICHIOMETRIC PEROVSKITE-TYPE OXIDES

The controlled synthesis of non-stoichiometric perovskite type oxides is of importance for fundamental and applied studies. The present cont ribution focuses on how data from thermal analysis, mainly thermogravi metry and X-ray powder diffraction, can be utilized for defining optim um synthesis conditions. The perovskite oxides frequently have (or are formed from binary oxides with) high stability and low reactivity. Th e synthesis of a homogeneous and pure reaction product is limited by d iffusion controlled mass transport, and precursor materials with mixin g of cations on a microscopic level are therefore needed. The decompos ition of citrate precursors, the formation and decomposition of interm ediates, the control of oxygen non-stoichiometry, the decomposition of the product and reactions/phase transitions on cooling are considered . As examples, thermal analysis data are provided and discussed for ma jor steps in the syntheses of non-stoichiometric LaMO(3) (M is V, Cr, Mn, Fe, Co or Ni).