A Displacive Structural Transformation in the CuO₂ Planes of YBa₂Cu₃Oₓ at the Underdoped-Overdoped Phase Separation Line

الأصل · EN

A structural phase transformation in the CuO₂ planes of YBa₂Cu₃Oₓ has been observed at the onset of the overdoped regime, x=6.95. We have measured as a function of x the dimpling in the CuO₂ planes by EXAFS, and the O2,3 in-phase (A₁g) mode by Raman scattering. The data show for x>6.95 anomalously large static displacements of the Cu2 atoms off the O2,3 layer, and a gap in the distribution of the O2,3 in-phase Raman shifts. We conclude the structure of overdoped YBa₂Cu₃Oₓ to be a martensitic form of the structure most favourable for the superconductivity, and possibly at the origin of the split superconducting transition in the overdoped regime.