A new layered cobaltite (Ga{sub 1/3}Co{sub 2/3}){sub 2}Sr{sub 2}CoO{sub 6+{delta}} with high spin Co{sup 3+}: modulated structure and physical properties
- Laboratoire CRISMAT, UMR CNRS-EnsiCaen 6508, 6 bd Marechal Juin, 1 4050 Caen Cedex (France)
Investigations in the Sr-Co-Ga-O system by means of transmission electron microscopy techniques have allowed the detection of a new layered cobaltite. Its structure has been obtained by combining high-resolution images and powder X-ray diffraction. The modulated structure of this novel oxide (Ga{sub 1/3}Co{sub 2/3}){sub 2}Sr{sub 2}CoO{sub 6+{delta}} is derived from the perovskite with a=a{sub p}{radical}2, b=a{sub p}{radical}2, c=19.2A and a modulation vector q*=q{sub 1}a*+q{sub 2}c*. For the as-prepared samples, the {delta} value is close to 0.4 and the modulated structure (q{sub 1}{approx}1/3 and q{sub 2}=1) can be described in an ideal orthorhombic 3D supercell Bb2b with the unit cell parameters a=3a{sub p}{radical}2=16.3030(5)A, b=5.4725(2)A and c=19.2034(4)A. The layer stacking consists in an intergrowth between a [SrCoO{sub 3}] perovskite-type block and a block of triple layers, [(SrO)(Co{sub 2/3}Ga{sub 1/3}O{sub 1+{delta}}{sub /2})(Co{sub 2/3}Ga{sub 1/3}O{sub 1+{delta}}{sub /2})] derived from [AO] rock-salt type layers. The magnetic study shows that the Co{sup 3+} cations exhibit a high spin state in this structure. The {theta}{sub p} value, -570K, suggests that antiferromagnetic interactions dominate in this compound as in the brownmillerite cobaltites. Nonetheless, its resistivity {rho}{sub 300K}=10{sup -1}{omega}cm is lower than that of the brownmillerite compounds. Since the positive Seebeck coefficient indicates the presence of holes (Co{sup 4+}) in the CoO{sub 2} conducting layers, the existence of weak ferromagnetic Co{sup 3+}-O-Co{sup 4+} interactions developing below {approx}150K is proposed to explain the electronic properties of this new oxide.
- OSTI ID:
- 20725837
- Journal Information:
- Journal of Solid State Chemistry, Vol. 178, Issue 3; Other Information: DOI: 10.1016/j.jssc.2004.12.035; PII: S0022-4596(04)00656-5; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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