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The double perovskites, AFe0.5Mo0.5O3with A=(Ba,Sr) or (Sr,Ca), were prepared by a sol-gel method, and the substitution effect at site A was studied by Mossbauer spectrometry. In the Mossbauer spectra of the double perovskite (Ba, Sr)Fe0.5Mo0.5O3, the isomer shifts decreased fromδ=0.72 mm/s to δ=0.4 mm/s and the internal magnetic fields increased with the increase of the Sr content. The Ba-rich samples were shown to contain superparamagnetic components under the same preparation conditions. Better crystallinity and larger hyperfine fields were obtained when 5% of the Sr-content of SrFe0.5Mo0.5O3was substituted by Ca as compared with substitution by Ba. Phonon density of states (DOS) of SrFe0.5Mo0.5O3substituted with Ca or Ba were obtained by nuclear inelastic scattering. The peaks of phonon DOS were shifted, depending on chemical compression/expansion of the lattice. The chemical pressure effect could be observed in the Mossbauer spectra and the phonon DOS spectra.

Resonant nuclear inelastic scattering (NIS) spectra of (Sr,Ca)(Fe,Co)O3- and (Ba,Ca)(Fe,Co)O3- were measured with the energy resolution of 3.5 MeV by detecting the 6.3 keV Fe K X-rays following after Mossbauer effect on 57 Fe transition excited by the monochromatized 14.41 keV synchrotron radiation. Both series of oxides annealed in air and in CO2 were examined. Soft phonon peak arising at ~8 MeV in NIS spectra of (Sr0.5Ca0.5)(Fe0.5Co0.5)O3- and (Ba0.5Ca0.5)FeO3- was found to be correlated with the oxygen ordering into brownmillerite structure, whereas more complex multi-phonon structure was observed in the spectra of less oxygen-deficient oxides such as (Sr0.95Ca0.05)(Fe0.5Co0.5)O3- and (Sr0.7Ca0.3)(Fe0.5Co0.5)O3- showing rather random distrubution of the oxygen vacancies. The changes in phonon DOS after CO2 absorbtion were also detected. Lam-Mossbauer factors of these oxides were calculated on the base of Debye Model.