The Role of the Fe/Mo Cations Ordering Degree and Oxygen Non‐Stoichiometry on the Formation of the Crystalline and Magnetic Structure of Sr₂FeMoO_6−δ

Abstract

Single‐phase Sr2FeMoO6−δ powders with various oxygen indices (δ) and degrees of the superstructural ordering (P) of the Fe/Mo cations are obtained from SrFeO2.52 and SrMoO4 reagents via solid‐state synthesis. It has been established by means of the X‐ray and neutron diffraction that, upon reducing the oxygen content and enhancing the superstructural ordering, the lengths of the Fe–O1 and Mo–O2 bonds in the crystal lattice increase, whereas the Fe–O2 and Mo–O1 bond lengths decrease. At the same time, the volume of the unit cell is reduced, which indicates an enhancement of the covalency degree of the bonds and stimulates a redistribution of the electron density, as well as an increase of the concentration of the spin‐down charge carriers located in the conduction band on the Mo(t2g)↓ orbitals. This circumstance leads to an increase of the density of states at the Fermi level, accompanied by an amplification of the exchange interaction and elevation of the Curie temperature, which points to the leading role of the spin‐polarized charge carriers at the Fermi level in the exchange interaction.

Challenges in Sr2FeMoO6−δ Thin Film Deposition

“…Contrarily to the view in this section, oxygen deficiencies δ were found to induce a superstructural ordering for samples with δ = 0.03…0.06 . However, XRD with superstructure peaks of different intensity were not related by the authors to a particular oxygen deficiency.…”

“…The authors of ref. [77] attribute the elevation of T C to an increase of free‐carrier concentration leading to a rise of the density of states at the Fermi level and, as a consequence, to an enhancement of exchange interaction. This explanation is in contradiction to ref.…”

“…The value of δ was determined only in a few number of reports . SFMO ceramics synthesized using SrCO 3 , Fe 2 O 3 , and MoO 3 powders as starting materials and applied to SFMO ceramics sintered at 1150 °C for 50 h in sealed ampoules together with Fe grains as oxygen trap possess an oxygen deficiency of δ ≈ 0.03 ± 0.02 as obtained by a redox method based on coulometric titration of both Fe 2+ and Mo 5+ in an inert Ar atmosphere .…”

“…This revealed values of δ = 0.132 and 0.296 for polycrystalline ceramic samples sintered in a flow of 5% H 2 /Ar gas mixture at 1160 °C for 9 and 15 h, respectively . By means of weighing the samples before and after their complete reduction in a hydrogen flux at 1100 °C for 20 h, values of δ = 0.03…0.06 were obtained in polycrystalline SFMO samples prepared by the solid‐state synthesis technique from SrFeO 2.52 and SrMoO 4 precursors and annealed in a flux of 5% H 2 /Ar gas mixture at 1150 °C for 5 h with a subsequent quenching to room temperature …”

Defect‐Induced Effects in Nanomaterials

“…Oxide materials. N. Kalanda et al performed thorough studies of the role of the Fe/Mo cations ordering degree and oxygen non‐stoichiometry on the formation of the crystalline and magnetic structure in the Sr 2 FeMoO 6− d double perovskites. P. Jozwik et al studied the accumulation and transformation of defects formed in bulk ZnO crystals at RT upon 300 keV Er ions bombardment using complementary techniques: Rutherford Backscattering Spectrometry in ion Channeling mode, X‐Ray reflectivity and X‐Ray diffraction.…”