Moessbauer studies of the system La/sub 1-x/Sr/sub x/Co/sub 1-y/Ti/sub y/O3

The system La/sub 1-x/Sr/sub x/Co/sub 1-y/Ti/sub y/O3 for (a) x = 0 and (b) x = y is investigated through Moessbauer spectroscopy measurements carried out between 77 and 800 K. None of the Moessbauer spectra show hyperfine splitting even at 77 K as Ti4+ substitution restricts the generation of Co4+ which is primarily responsible for itinerant electron ferromagnetism in La/sub 1-x/Sr/sub x/CoO3. In all the samples, two resonances are observed expect in the samples with y = 0.3 and 0.5 in the system (a) where three resonances are observed. Three resonances are assigned to low spin cobalt states (i.e. Co/sup II/, Co/sup III/ and Co/sup IV/), high spin Co3+ (t/sub 2g//sup 4/e/sub g//sup 2/) and high spin Co2+(t/sub 2g//sup 5/e/sub g//sup 2/) states, the first two being common in all the samples. The variation of the isomer shift and other data with temperature is discussed in the framework of spin-state and valence-state equilibria of cobalt ions in these materials. The difference in behaviour between the systems (a) and (b) is explained in terms of generation of different valence and spin states of cobalt with the increase in x and is further compared with the system La/sub 1-x/Sr/sub x/CoO3. The susceptibility, electron transport, and other data reported earlier support the results obtained from Moessbauer studies. (author)