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Origin of the metal-insulator transition in the superconducting series Bi2Sr2Ca1−xYxCu2O8+δ

Physica C Superconductivity
Publication Date
DOI: 10.1016/0921-4534(93)90977-x
  • Physics


Abstract The metal-insulator transition in the solid solution Bi 2Sr 2Ca 1−xY xCu 2O 8+δ (0≤ x≤1) has been investigated by TGA (oxygen content) and by X-ray absorption spectroscopy (Bi and Cu valence states). Resistivity and AC magnetic susceptibility measurements have shown that the superconducting properties and the metallic behavior vanish for x>0.55. The oxygen content δ is larger than x/2 for x≤0.3 and smaller than x/2 for x≥0.6. For x=0, the Cu K edge shows a shift towards high energy with respect to the Cu(II) oxide La 2CuO 4; this shift decreases with increasing x in agreement with the decrease of the doping hole density and the variations of the physical properties. For 0≤ x≤0.3, the Bi L 3 edge shows a shift of 1 eV towards low energy with respect to the Bi(III) oxide Bi 2O 3 in agreement with the charge transfer between [CuO 2] ∞ and [BiO] ∞ planes. This shift also decreases with increasing x, but is still present for the x=0.6 composition for which δ is smaller than x/2. A model of the metal-insulator transition in this series is proposed based on the fact that the intercalation of excess oxygen raises the bottom of the Bi-O band with respect to the Fermi level and decreases the contribution of the Bi-O electron pocket to the hole density.

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