New Low-Frequency Relaxation Process in La₂CuO_4+δ by Internal Friction Experiments

The low-frequency relaxation internal friction spectrum of La₂CuO_4+δhas been measured from -170 to 200°C in an automatic torsion apparatus at frequencies between 0.1 and 5.0Hz. Three new relaxation processes are found with maxima, which are attributed to thermally activated diffusive jumps of oxygen atoms or vacancies in the oxygen sublattice, according to various activation enthalpies of three experimental runs. It is shown that the content of oxygen defect have important influences on the physical properties of La₂CuO_4+δ.