title: The defect structure and chemical lattice strain of the double perovskites Sr2BMoO6-δ (B = Mg, Fe).
abstract: The defect structure of B-site ordered double perovskites Sr2BMoO6-δ was analyzed. The defect structure model was proposed and successfully verified using data on oxygen nonstoichiometry of Sr2MgMoO6-δ and Sr2FeMoO6-δ. As a result, equilibrium constants of the defect reactions involved were estimated. Fe and Mo in Sr2FeMoO6-δ were found to be in the mixed oxidation state close to +2.5 and +5.5, respectively. Chemical strain of the Sr2FeMoO6-δ double perovskite lattice was studied by in situ high temperature XRD at 1100 °C depending on pO2. Parameter a of the Sr2FeMoO6-δ cubic cell was found to increase with decreasing pO2 because of lattice chemical expansion. The tetragonal polymorph of Sr2FeMoO6-δ was shown to exhibit transversal isotropy with respect to chemical expansion. It was also found that its crystal lattice expands in the ab-plane and simultaneously contracts along the c-axis when the oxygen content in the double perovskite decreases. In order to describe the degree of anisotropy of chemical strain a new phenomenological coefficient was introduced. This coefficient was shown to affect both the magnitude and change direction of an oxide cell volume caused by its reduction/oxidation. Excellent agreement between the chemical expansion along the a-axis calculated for both polymorphs of Sr2FeMoO6-δ according to the model recently developed and that measured experimentally was shown. Chemical contraction observed along the c-axis with a decreasing oxygen content in the tetragonal polymorph was also found to coincide completely with that calculated using the approach developed in the present study.
authors.affiliation: Department of Chemistry, Institute of Natural Sciences, Ural Federal University, Ekaterinburg, 620000, Russia. dmitry.tsvetkov@urfu.ru.
authors.forename: D S
authors.initials: DS
authors.lastname: Tsvetkov
authors.affiliation: Department of Chemistry, Institute of Natural Sciences, Ural Federal University, Ekaterinburg, 620000, Russia. dmitry.tsvetkov@urfu.ru.
authors.forename: I L
authors.initials: IL
authors.lastname: Ivanov
authors.affiliation: Department of Chemistry, Institute of Natural Sciences, Ural Federal University, Ekaterinburg, 620000, Russia. dmitry.tsvetkov@urfu.ru.
authors.forename: D A
authors.initials: DA
authors.lastname: Malyshkin
authors.affiliation: Department of Chemistry, Institute of Natural Sciences, Ural Federal University, Ekaterinburg, 620000, Russia. dmitry.tsvetkov@urfu.ru.
authors.forename: A S
authors.initials: AS
authors.lastname: Steparuk
authors.affiliation: Department of Chemistry, Institute of Natural Sciences, Ural Federal University, Ekaterinburg, 620000, Russia. dmitry.tsvetkov@urfu.ru.
authors.forename: A Yu
authors.initials: AY
authors.lastname: Zuev