Ba2Co9O14: New Inorganic Building Blocks with Magnetic Ordering through Super-Super Exchanges Only
详细信息 查看全文
- 作者：Ghislaine Ehora ; Sylvie Daviero-Minaud ; Marie Colmont ; Gilles André ; Olivier Mentré
- 刊名：Chemistry of Materials
- 出版年：2007
- 出版时间：May 1, 2007
- 年：2007
- 卷：19
- 期：9
- 页码：2180 - 2188
- 全文大小：621K
- 年卷期：v.19,no.9(May 1, 2007)
- ISSN：1520-5002
文摘
Ba2Co2+3Co3+6O14 has been prepared by conventional solid-state reaction between BaO2 and CoO. Itscrystal structure has been refined from single-crystal X-ray diffraction data and powder neutron diffraction,a = 5.6963(8) Å, c = 28.924(6) Å, space group R
m, Z = 3, R1 = 4.44%, wR2 = 10.96%. It showsevidence of new building blocks called T' (ch'h'c stacking sequence of cubic O4 and hexagonal BaO3layers) by analogy with the related T-blocks (hh'h'h) of the barium hexaferrites. T' consists of CoII,IIIO2brucite-like layers pillared by CoIIO4 tetrahedra and CoIII3O12 octahedral trimers. Below TN = 39 K,tetrahedral and octahedral high spin CoII (S = 3/2) diluted in the framework mainly containing low spinCoIII (S = 0) interact through CoII-O-O-CoII through super-super exchanges (SSE) only. The analysisof the competition between the multiple SSE paths has been performed through geometrical considerations.The magnetic moments are lying antiferromagnetically in the a,b plane in good agreement with themagnetic group theory presented in our work. Their values of 1.70(4) 
B and 2.83(3) B for the octahedraland tetrahedral CoII, respectively, are explained by the high degree of covalency and magnetic transfertoward the surrounding anions involved in the SSEs. At high temperature, the creation of oxygen vacanciesis observed and strongly intervenes in the hopping conductivity as shown from the abrupt change in thematching Arrhenius law. This particular feature demonstrates potential mixed conductivity processes inthe medium-temperature range. At 1000 
C, it reversibly decomposes into CoO and BaCoO3-
. Finally,the medium crystallinity of the title compound is explained by the presence of defects and intergrowthswith other hexagonal perovskites of the Ba-Co-O system.
m, Z = 3, R1 = 4.44%, wR2 = 10.96%. It showsevidence of new building blocks called T' (ch'h'c stacking sequence of cubic O4 and hexagonal BaO3layers) by analogy with the related T-blocks (hh'h'h) of the barium hexaferrites. T' consists of CoII,IIIO2brucite-like layers pillared by CoIIO4 tetrahedra and CoIII3O12 octahedral trimers. Below TN = 39 K,tetrahedral and octahedral high spin CoII (S = 3/2) diluted in the framework mainly containing low spinCoIII (S = 0) interact through CoII-O-O-CoII through super-super exchanges (SSE) only. The analysisof the competition between the multiple SSE paths has been performed through geometrical considerations.The magnetic moments are lying antiferromagnetically in the a,b plane in good agreement with themagnetic group theory presented in our work. Their values of 1.70(4) B and 2.83(3) B for the octahedraland tetrahedral CoII, respectively, are explained by the high degree of covalency and magnetic transfertoward the surrounding anions involved in the SSEs. At high temperature, the creation of oxygen vacanciesis observed and strongly intervenes in the hopping conductivity as shown from the abrupt change in thematching Arrhenius law. This particular feature demonstrates potential mixed conductivity processes inthe medium-temperature range. At 1000 C, it reversibly decomposes into CoO and BaCoO3-. Finally,the medium crystallinity of the title compound is explained by the presence of defects and intergrowthswith other hexagonal perovskites of the Ba-Co-O system.