The physical properties of an oxygen stoichiometric sample, YBaCo4O7, have been studied by T-dependent measurements of the electrical resistivity (p), Seebeck coefficient (S) and magnetization. Its structural characterization by X-ray diffraction reveals an orthorhombic crystallo-graphic cell at room temperature (Pbn2(1) space group, a = 6.298 angstrom, b = 10.939 angstrom and c = 10.228 angstrom). In that structure made of corner shared CoO4 tetrahedra, the magnetic array of the cobalt cations form a 1: 1 regular stacking of Kagome and triangular layers. All the physical measurements point towards an hysteretic transition in the range 300-310 K, with a sharp increase of both S and p at T-S as the temperature decreases. A clear similarity to other LBaCo4O7 compound (L = lanthanide) is found, supporting strongly the existence of a structural transition at TS. It is also shown that the ionic radius of the L cation governs T-S. (c) 2006 Elsevier Masson SAS. All rights reserved.
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