1212-Molybdo-Cuprates; effect of oxygenation in the structure, properties and electronic states
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1212-Molybdo-Cuprates; effect of oxygenation in the structure, properties and electronic states Sourav Marik1, 2, A. J. Dos santos-Garcia1, 3, Christine Labrugere2, Emilio Morán1, Olivier 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) ABSTRACT The influence of oxygenation in the magnetism, superconductivity and electronic states for the Mo0.3Cu0.7Sr2RECu2Oy (RE = Y, Er and Tm) compounds are discussed here. The magnetic measurements on the as-prepared (AP) samples suggest the existence of short-range magnetic correlations due to the presence of the paramagnetic MoV cations in the copper chain site. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high pressure oxygenated sample shows the highest superconducting transition temperature of TC = 84 K. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of X-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP material; annealing under flowing oxygen enhances both the MoVI and CuII amounts. A detailed study of the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy samples has been performed and is also discussed. INTRODUCTION In recent years, layered cuprates have attracted much interest in the scientific community for their ability to host a variety of functional properties, especially high temperature superconductivity (HTSC). The structure of CuBa2YCu2O7-δ (YBa2Cu3O7-δ, YBCO, Y-123) and related phases contain two crystallographically distinct Cu sites: the chain site (Cu1, CuO chain) and the square–pyramidal or planar site (Cu2, CuO2 planes). CuO chain layers can act as a charge reservoir by supplying the carriers necessary for the superconductivity to take place in the CuO2 planes. Pure CuSr2YCu2O7-δ (YSr2Cu3O7-δ or YSCO, TC = 60 K), the strontium analog of ‘‘123’’ superconductor YBCO, can only be prepared at very high pressure.1 But these phases can be stabilized at ambient pressure by substituting Pb, Al, Ti, Fe, W, Mo, and Ga partially or completely for Cu in the chains.2-5 Although, the rare earth planes in CuBa2RECu2O7-δ (REBCO, RE = rare earth cations) and related phases are well isolated from each other and sandwiched between two CuO2 planes, three-dimensional (3D) magnetic ordering has been discovered in the compounds with RE =Er, Gd, Dy, and Nd.6,7 CuBa2TmCu2O7-δ (TmBCO)8 shows relatively strong paramagnetism compared to other CuBa2RECu2O7-δ 6,7 compounds (RE =Er, Gd, Dy, and Nd); such behaviour
has been mainly attributed to the strong Tm-magnetic anisotropy that operates in b
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