Metal-insulator transition near oxygen content parameter δ ≃ 0.018 was observed for electron-doped Pr1.85 Ce0.15 CuO4+δ (-0.003 ≤ δ ≤ 0.03 cuprates. Cu K -edge X-ray absorption near-edge structure (XANES) studies with nearly identical threshold edge energy Eo of 8980.8 eV indicate a Cu formal valence smaller than 2 for all samples, which is consistent with the estimated Cu valence of ∼ 1.84 for 20.5 K superconductor Pr1.85 Ce0.15 CuO3.997 and ∼ 1.91 for Pr1.85 Ce0.15 CuO4.03 insulator. The XANES spectrum reflects the Cu 3dn character where low energy peak A1 reflects the 3d10 configuration of Cu(I) oxidation state and A2 peak reflects the 3d10 L (L for a oxygen ligand hole) configuration for Cu(II) oxidation state. The variation of energy separation Δ E (A2-A1) is consistent with the observed metal-insulator transition, increases sharply from 2.42 e V for Pr1.85 Ce0.15 CuO4.018 insulator to 2.74 e V for 15 K underdoped superconductor Pr1.85 Ce0.15 CuO4.015.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Materials Science(all)
- Condensed Matter Physics