Excess oxygen diffusion in La2cuo4+? investigated by mechanical spectroscopy

Abstract

The diffusion of excess oxygen atoms in La2CuO4+δ, (0 < δ < 0.035) was studied by mechanical spectroscopy with a vibrating reed method (220 Hz<f< 1.3kHz; 4K < T < 380K). For samples with δ=0.013(2) we observe a very large internal friction peak (Tmax=275K, f=0.22kHz). It shifts to higher temperatures with increasing frequencies indicating a thermally activated relaxation behavior with an activation enthalpy of 0.31(3) eV. The relaxation peak vanishes after vacuum annealing the sample (δ ≈0) leading to the conclusion that the relaxation peak is due to the diffusion of excess oxygen atoms. A relaxation peak of similar strength as in the sample with δ =0.013 is also detected in an oxygen enriched sample (δ = 0.035). This unexpected finding of the relaxation strength is discussed in terms of the proposed phase diagrams for La2CuO4+δ. In addition, a shoulder at the high temperature wing of the strong relaxation peak is seen the position of which does not vary with the vibration frequencies.