Non-isothermal crystallization kinetics of the heavy-group lanthanide dititanates

The systematic investigation of crystallization kinetics of heavy-group lanthanide dititanate pyrochlores, HL2Ti2O7 (HL=Lu, Tm, Er, Ho, Y, Dy, and Tb) is presented. Materials are prepared by the Pechini-type polymerized complex route, and their thermal properties were studied by differential thermal analysis under non-isothermal conditions. For this group, the crystallization temperature became larger with increasing the ionic radius of lanthanides, from 1066 K for Lu2Ti2O7 to 1125 K for Tb2Ti2O7. The linear dependence of crystallization temperature on radius of heavy lanthanide ions is found to follows Tc[K]=168.86+920.89×rion[Å] semi-empirical equation. Apparent activation energies of crystallization were obtained from calculations based on the Arrhenius equation, isoconversional method and Pérez-Maqueda method, and are ∼805 kJ mol−1 calculated by three different methods. The crystallization kinetics followed the so-called Avrami-Erofeev (A3) model, as confirmed using several criteria, namely, the Málek, master plot, and Pérez-Maqueda methods. The crystallization mechanism of all lanthanide dititanate pyrochlores is found to be the same, and the crystallization process involves a constant rate of nucleation and two-dimensional growth of nuclei.