Raman analysis of asymmetrical chains in YBa2CuO7-δ films

초록

YBa2Cu3O7-delta/MgO(1 0 0) thin films with depletion of oxygen have been studied with Raman spectroscopy. The depletion changes the intensity of 233 and 596 cm(-1) phonons induced from Cu(1)-O(1) asymmetrical chains. A simple model of a symmetry-broken chain row is introduced to explain this phenomenon. With depletion, the row is configured as asymmetrical [O(1)-Cu(1)-o(1)] chains, where O(1) and o(1) are full and deficient oxygen in the orthorhombic and tetragonal structures, respectively. The Raman peaks at 233 and 596 cm-1 increase with an increase in a population density of the asymmetrical chains in the row and decrease as the row has more symmetric sites of full or deficient oxygen. As a result, the intensity of the chain-induced modes reflects a degree of the opposite structure involved in the phase transition in a single-phase film, which is verified by both the relative intensity of the 232 cm(-1) phonon and the full width at half maximum of a Cu(2) superposition band from the coexisting phases in the film. All the results support the asymmetrical-chain model. (c) 2007 Elsevier B.V. All rights reserved.

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