Kinetics and thermodynamics of B-site cation order in (Sr,Ba)2FeSbO6 perovskite

Several sample series of the (Sr0.5Ba0.5)2FeSbO6 double-perovskite compound are synthesized under various heat-treatment conditions starting from a sol-gel prepared precursor to investigate the kinetics and thermodynamics of the B-site cation ordering. The synthesis yields samples with different levels of Fe/Sb ordering ranging from essentially disordered up to fully ordered depending on the synthesis temperature and duration. In the temperature range 1050–1200°C the degree of order is kinetically controlled following Johnson-Mehl-Avrami-Kolmogorov type kinetics, while at 1300°C the thermodynamic equilibrium is quickly reached such that higher than 95% ordering degrees are obtained in heat-treatment periods as short as couple of hours. Also importantly, for the differently synthesized single-phase samples a linear relationship between the degree of order and the cubic sub-cell dimension is seen.