Abstract
Polycrystalline samples La2 − xSr x CuO4 − δ (0.06 ≤ x ≤ 1.0) and the corresponding vacuum annealed samples were investigated systematically by means of XRD, infrared (IR) spectra, ESR, and resistivity. It is found that the doping of Sr and the oxygen vacancies in CuO2 planes show different effects on the lattice parameters a and c, and the changes of a and c of La2 − xSr x CuO4 − δ samples (x ≥ 0.2) rest with the cooperation of the two factors. The two high frequency IR vibration modes at 500 and 689 cm−1, which are referred to the vibrations of apical oxygen and planar oxygen, are analyzed in detail. The disappearance of the mode at 689 cm−1 is interpreted in terms of the screened effect of charge carriers in CuO2 planes. ESR results indicate that oxygen deficiency of CuO2 layers not only decreases carrier concentration, but also destroys the antiferromagnetic spin correlation or spin fluctuation and results in localized Cu2+ spins. The effect of localized Cu2+ spins (or spin scattering) on the superconductivity and transport properties is discussed in the text.
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