Kinetics and Thermodynamics of the Degree of Order of the B Cations in Double-Perovskite Sr₂FeMoO₆

Here we show that the B -site cation (Fe/Mo) ordering in the double-perovskite magnetoresistor, Sr 2 FeMoO 6, is controlled by either kinetics or thermal equilibrium depending on the temperature range. To enhance the ordering, long synthesis periods at moderate temperatures are thus required. Employment of a special oxygen-getter-controlled low-O 2 -pressure encapsulation technique for the sample synthesis enabled us to use long heating periods without evident evaporation of Mo, and thereby reach the thermal equilibrium state and a high degree of B -site cation order. For samples fired at 1150 °C for long periods (≥36 h), record-high M S values of 3.7−3.9 μ B were obtained.