New 1212-Molybdo-Cuprate phases using High pressure and high temperature synthesis
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New 1212-Molybdo-Cuprate phases using High pressure and high temperature synthesis Sourav Marik1, 2, A. J. Dos santos-Garcia1, 3, Emilio Morán1, O. Toulemonde2, M. A. Alario-Franco1* 1 Dpto. Química Inorgánica, Facultad de CC.Químicas, Universidad Complutense de Madrid, 28040-Madrid (Spain) 2 CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, Pessac, F-33608, France 3 Dpto. Química Industrial y Polímeros, E. U. I. T. I, Universidad Politécnica de Madrid, 28012, Madrid (Spain) * E mail: [email protected] ABSTRACT New 1212- type Molybdo-Cuprates of with composition Mo0.5Cu0.5Sr2RECu2O7.5 (RE = Rare Earth) have been prepared by High Pressure and High Temperature (HPHT) synthesis. Their crystal structures are characterized by combining the X-Ray/Neutron powder diffraction and electron diffraction techniques. All the materials show tetragonal symmetry, crystallizing in the P4/mmm space group (S.G.). The chain oxygens are randomly distributed in the two different oxygen sites, which are not completely filled and the defect induced by oxygen vacancies in fact makes the chain fragmented and disordered. The microstructure of these compounds is interpreted by a well-known diagonal cell √2ap × √2ap × 3ap, as confirmed by the Electron diffraction (ED) and transmission electron microscope (TEM). X-ray photoelectron spectroscopy (XPS) studies show the predominance of the non magnetic MoVI state over the MoV one. At the same time oxidation state of copper is found to be dominated by CuII. INTRODUCTION Since the discovery of high temperature superconductivity (SC) in YBa2Cu3Oy (YBCO), most of the work devoted to the search of high temperature superconductors has relied upon the synthesis of new materials derived from YBa2Cu3Oy and, in particular, upon the substitution of one of the copper atoms located in the so-called charge reservoir layer (CRL).1 The 1212−type layered cuprates with general formula MA2RECu2O8 or M – 1212 (where M is commonly a transition metal element, A is an alkaline earth metal, and RE is a rare earth ion), iso-structural with the classical YBa2Cu3Oy (YBCO or Cu−1212) in which Y, Ba, and Cu1 (the chain copper site) are completely or partially replaced with rare earth elements, alkaline earth metal, and transition metal ions, respectively. Obviously, the valance state of substituent cation plays an important role in controlling the effective copper valance (p).2 In particular; cation substitution at the Cu-sites may change p and affect the physical properties accordingly [see ref. 2 and the references therein]. Coexistence of Weak ferromagnetism (WFM) and superconductivity (SC) have even been discovered in the ruthenocuprate with nominal composition RuSr2GdCu2O8.3,4 Depending on the magnetic state of the substituted transition metal ion, other 1212 compounds show a wide diversity of electronic properties.3-12 However, at room pressure, not all the members of 1212 type compounds can be made. The use of high pressure has proven very useful in this context.12-16 Recently, and contrary to previous
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