A comparative study on the kinetics and mechanism for the formation of R2Ba4Cu6O13 (R = Y, La, Nd, Sm, Eu or Er) from citrate precursors using non-isothermal TG

The kinetics and mechanism of the two-step reactions occurring in the precu rsor powders for the formation of the R2Ba4Cu6O13 (R = Y, La, Nd, Sm, Eu or Er) by citrate-fire method were studied by employing dynamic TG at linear heating rates of 5, 10 and 20 degreesC/min in static air. The two-step reac tion sequence occurring in the precursors comprising essentially R(OH)(3) ( or RO(OH)/R2O3), BaCO3 and CuO were analyzed by the integral approach using 23 functional forms for G(alpha). In the case of Y or La bearing precursor s, the first step leading to the partial formation of BaCuO2 and R2Cu2O5 fo llowed PT4 mechanism while the final weight loss of CO2 corresponding to th e formation of R2Ba4CU6O13 followed the 1D diffusion. However, in the case of other lanthanides (Nd, Sm, Eu and Er) the mechanisms were found to be 2D diffusion for the first step (partial formation of BaCuO2 and R2CuO4) and 3D diffusion for the final step corresponding to the loss of CO2 from remai ning BaCO3 leading to the formation of R2Ba4Cu6O13. (C) 2001 Elsevier Scien ce B.V. All rights reserved.