Kinetics and Thermodynamics of the Degree of Order of the <i>B</i> Cations in Double-Perovskite Sr₂FeMoO₆

Abstract

Here we show that the B-site cation (Fe/Mo) ordering in the double-perovskite magnetoresistor, Sr2FeMoO6, 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-O2-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 MS values of 3.7−3.9 μB were obtained.