Metal-insulator transition and Cu K-edge XANES studies for Pr1.85Ce0.15CuO4+δ high-Tc superconductors

[[abstract]]A metal-insulator transition near oxygen content parameter δ ≃ 0.018 was observed for electron-doped Pr1.85Ce0.15CuO4+δ (-0.003 ⩽ δ ⩽ 0. 03) cuprates. Cu K-edge X-ray absorption near-edge structure (XANES) studies with nearly identical threshold edge energy E0 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 Pr1.85Ce0.15CuO3.997 and ~ 1.91 for Pr1.85Ce0.15CuO4.03 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 3d10L_(L_for a oxygen ligand hole) configuration for Cu(II) oxidation state. The variation of energy separation ΔE(A2-A1) is consistent with the observed metal-insulator transition, increases sharply from 2.42 e V for Pr1.85Ce0.15CuO4.018 insulator to 2.74 eV for 15 K underdoped superconductor Pr1.85Ce0.15CuO4.015[[fileno]]2010102010221[[department]]物理