New Mixed Valent Ferrites (Tl1.5Hg0.5)Sr3−xBaxFe2O9−δ(0≤x≤2) with the Tl-2212-Type Structure

✍ Scribed by N. Nguyen; D. Groult; P. Boullay; C. Michel; B. Raveau

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 679 KB
• Volume: 132
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7464

✦ Synopsis

A new series of layered ferrites (Tl 1.5 Hg 0.5 )Sr 3؊x Ba x Fe 2 O 9؊ has been synthesized and characterized for the composition range 04x42. The structure has been refined from powder XRD data and shown to be similar to that of the tetragonal Tl-2212type superconducting copper oxides. Electron diffraction and high-resolution electron microscopy studies reveal a regular stacking of the [(Tl, Hg)O], [(Sr, Ba)O] and [FeO 2 ] layers without defects or atomic ordering on both the (Tl, Hg) and (Sr, Ba) sites. Magnetic susceptibility measurements and 57 Fe-Mo¨ssbauer spectroscopy have been performed for (Tl 1.5 Hg 0.5 ) Sr 2 BaFe 2 O 9؊ . They provide evidence for antiferromagnetic ordering below 50 K with localized Fe 3؉ and Fe 4؉ species at 4.2 K, while intermediate valence states due to electron delocalization between iron sites must be taken into account at 293 K. The role of mercury is discussed.