Local structure studies of the underdoped-overdoped transition in YBa_2Cu_3O_x. Measurement of the yttrium y-ray absorption fine structure

J. Röhler; P. W. Loeffen; S. Müllender; K. Conder; E. Kaldis

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Local structure studies of the underdoped-overdoped transition in YBa_2Cu_3O_x. Measurement of the yttrium y-ray absorption fine structure

J. Röhler·P. W. Loeffen·S. Müllender·K. Conder·E. Kaldis

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Abstract

We have measured the extended x-ray absorption-fine-structure (EXAFS) at the Y-K edge of YBa_2Cu_3O_x for x=6.801, 6.947, 6.968, 6.984 at T=20-300 K. Across the underdoped-overdoped transition the Y-Cu2 pairs exhibit harmonic vibrations which freeze out in the superconducting phase, whereas the Y-O2,3 pairs exhibit strong anharmonicities with a singularity at T_c. In the underdoped regime the average spacing O2,3-Cu2 increases with x due to displacements of Cu2 towards Ba, but the average position of O2,3 along c is almost unaffected. Optimum doping is a notable point in the x-T phase diagram, also concerning the lattice degrees of freedom. Here the O2,3-Cu2 spacing (buckling) is largest, and in the superconducting phase the Cu2 position along the c-axis is independent on temperature. In the overdoped regime increasing x displaces the Cu2 along c further towards Ba, but the O2,3 layer starts to shift in the same direction, thus decreasing the O2,3-Cu2 spacing.

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J. Röhler, P. W. Loeffen, S. Müllender, K. Conder, E. Kaldis. 1997-01-29. Local structure studies of the underdoped-overdoped transition in YBa_2Cu_3O_x. Measurement of the yttrium y-ray absorption fine structure. https://arxiv.org/abs/cond-mat/9701208

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