Electrical conductivity measurements show that Ln1-x Sr x CoO3, (Ln = Pr or Nd) undergoes a non-metal-metal transition when x≈0 3. The d.c. conductivity of compositions with 0<x<0.l obeys the T−1/4law up to 400 K and the a.c. conductivity data follow the ωδ law with δ in the range 0.6–0.8. Surprisingly, however, δ seems to increase with increasing temperature. Thermopower measurements show clear evidence for a change in the mechanism of conduction (around 350 K) from variable range hopping to transport at E c. All these transport properties suggest that Co4+ ions in Ln1-x Sr x CoO3 (0<x<0.1), considered as moving in a lattice of Co3+, form a degenerate gas and that the states at the Fermi energy are Anderson localized.
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