Evidence for non-adiabatic, small-polaron-mediated transport both above and below the ferromagnetic ordering temperature in O-depleted La0.67Ca0.33MnO3-delta

The transport and magnetic behaviours of Ar-annealed (O-depleted) bulk samp les of an archetypal, 'optimally' doped manganese perovskite, La0.67Ca0.33M nO3, are reported, analysed and compared with those of an untreated specime n. These indicate that the transport data for both the paramagnetic and fer romagnetic phases of the O-depleted system are consistent with the predicti ons based on polaronic hopping, specifically non-adiabatic small-polaron ho pping ton the basis of the internal consistency of estimates for the charac teristic frequency Omega (0) from both the adiabatic and non-adiabatic form alisms). These results yield indirect support for models which attribute tr ansport in doped perovskites in general, and the colossal-magnetoresistance phenomenon in particular, to polaronic behaviour.