Combined effects of hole doping and off-stoichiometry on the structures, transport, and magnetic properties of Sr(2−y)NayFe(1−x)Mo(1+x)O6 (x = 0/5x = y; y = 0, 0.05, 0.1, 0.15, 0.2, and 0.3). Issue 42 (16th May 2017)

• Record Type: Journal Article
• Authors: Wang, Jin-Feng; Zhang, Yan-Ming
• Is Part Of: RSC advances. Volume 7:Issue 42(2017)
• Page Start: 26185
• Page End: 26193
• Publication Date: 2017-05-16
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7ra02919e
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Composition-dependent T C values in Sr(2− y ) Na y Fe(1− x ) Mo(1+ x ) O6 ( x = 0/5 x = y ; y = 0, 0.05, 0.1, 0.15, 0.2, and 0.3) do not monotonously depend on the carrier density. Abstract : A series of double perovskite, Sr(2− y ) Na y FeMoO6 ( y = 0, 0.05, 0.1, 0.15, 0.2, and 0.3) and Sr(2− y ) Na y Fe(1− x ) Mo(1+ x ) O6 (5 x = y ; y = 0.05, 0.1, 0.15, 0.2, and 0.3), ceramics were synthesized via a solid-state reaction. The influences of the doped Na ( y ) and off-stoichiometry (excess Mo: x ) content on the structure, magnetization, chemical states, resistivity, magnetoresistance (MR), and the Curie temperature ( T C ) were systematically and comparatively investigated. The X-ray diffraction results indicated that the Fe/Mo ordering degree in Sr(2− y ) Na y FeMoO6 and Sr(2− y ) Na y Fe(1− x ) Mo(1+ x ) O6 exhibited a slight suppression for y = 0–0.15, whereas a significant decrease was observed for y = 0.2 and 0.3. X-ray photoelectron spectroscopy results confirmed that the chemical states of Fe and Mo cations in all the samples had +3 and +5 valences. With the decreasing y values, it was observed that the saturated magnetization M s demonstrated a gradual decrease, in good agreement with the suppression of the Fe/Mo ordering degree. This close correlation between the magnetic properties and the Fe/Mo ordering degree indicates that the magnetic behaviors are predominantly controlled by the ordering degree of Fe/Mo in all the ceramics. The MR behavior in the samples is mainly determined by the grain boundary conditions. Upon comparing Sr(2− y ) Na y FeMoO6 with Sr(2− y ) Na y Fe(1− x ) Mo(1+ x ) O6 (5 x = y ) for the same y value, Sr(2− y ) Na y Fe(1− x ) Mo(1+ x ) O6 (5 x = y ) showed a decreased grain boundary strength (the resistivity); thus, a diminished MR performance was observed, indicating that introducing excess Mo into the hole-doped Sr2 FeMoO6 system was disadvantageous for practical applications. Interestingly, the T C of both Sr(2− y ) Na y FeMoO6 and Sr(2− y ) Na y Fe(1− x ) Mo(1+ x ) O6 (5 x = y ) gradually decreased until y = 0.15, but improved on further increasing the y value. This composition-dependent tendency of T C cannot be explained only on the basis of the itinerant electron density, which is responsible for the optimized T C in the electron-doped Sr2 FeMoO6 systems.