Oxygen Mobility in Polycrystalline NiCr 2 O 4 and α‐Fe 2 O 3

Oxygen diffusion coefficients have been determined for polycrystalline samples of NiCr 2 O 4 and α‐Fe 2 O 3 by exchange measurements with oxygen gas containing the stable isotope 18 O, using mass spectrometer analysis. Oxygen diffusion in NiCr 2 O 4 can be represented by the equation D = 0.017 exp (‐65,400/RT); oxygen diffusion in α‐Fe 2 O 3 can be represented by the equation D = 1 × 10 11 exp (‐146,000/RT). The large difference between D 0 and activation energy for these materials suggests that different diffusion mechanisms are involved.