Mixed Metallic Ba(Co,Fe)X0.2O3鈭捨?/sub> (X = F, Cl) Hexagonal Perovskites: Drastic Effect of Fe-Incorporation on Structural and Electronic Features
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- 作者：Mihaela Iorgulescu ; Pascal Roussel ; Nathalie Tancret ; Nicolas Renault ; Florence Porcher ; Gilles Andr茅 ; Houria Kabbour ; Olivier Mentr茅
- 刊名：Inorganic Chemistry
- 出版年：2012
- 出版时间：July 16, 2012
- 年：2012
- 卷：51
- 期：14
- 页码：7598-7608
- 全文大小：670K
- 年卷期：v.51,no.14(July 16, 2012)
- ISSN：1520-510X
文摘
Starting from the parent 10H鈥揃a5Co5X1鈥?i>xO13鈭捨?/sub> (trimeric strings of face-sharing CoO6 octahedra with terminal CoO4 tetrahedra, stacking sequence (chhch鈥?2) and 6H鈥揃a6Co6X1鈥?i>xO16-未 (similar with tetrameric strings, stacking sequence chhhch鈥? hexagonal perovskites forms (X = F, Cl; c, h = [BaO3] layers ; h鈥?= [BaOX1鈥?i>y] layers), we show here that the Fe incorporation leads to large domains of solid solutions for both X = F and Cl but exclusively stabilizes the 10H-form independently of the synthesis method. In this form, the lowest concentration of h-layers is stabilized by a sensitive metal reduction with increasing the Fe ratio. In a more general context of competition between several hexagonal perovskite polymorphs available for most of the transition metals, this redox change is most probably the key factor driving 1D (face-sharing chains) to 3D (corner-sharing) connectivities. Strikingly, ND data evidence the location of oxygen deficiencies in the tetrahedral (Co/Fe) coordination. This effect is exaggerated at high temperature, while (Co/Fe)O4-未 coordinations are completed by the displacement of X鈥?/sup> anions toward the (Co/Fe) sphere of coordination following a 鈥?i>push-and-pull鈥?mechanism within h鈥测€揫BaOX1鈥?i>y] layers. The Fe-incorporation is also accompanied by increasing conduction gaps with predominant 1D variable range hopping. The full series show antiferromagnetic behavior with increasing TN as [Fe] increases. For Fe-rich compounds TN is estimated about 600 K, as rarely observed for hexagonal perovskite compounds. Finally, magnetic structures of all iron-doped compounds show a site-to-site AFM ordering, different of the magnetic structure of Co-only parent compounds. Here, DFT calculations predict low-spin octahedral Co configurations, but high-spin Fe species in the same sites.