Chemical ordering and magnetic phase transitions in multiferroic BiFeO_(3)-AFe_(1/2)Sb_(1/2)O_(3)(A-Pb,Sr)solid solutions fabricated by a high-pressure

synthesisCeramic samples of BiFeO_(3)-based perovskite solid solutions with the highly ordered complex perovskites PbFe_(1/2)Sb_(1/2)O_(3)(PFS)and SrFe_(1/2)Sb_(1/2)O_(3)(SFS)were obtained using high-pressure synthesis at 4-6 GPa.Mössbauer studies revealed that BiFeO_(3)-SFS compositions are characterized by a larger compositional inhomogeneity as compared to BiFeO_(3)-PFS ones.In line with this result,concentration dependence of the magnetic phase transition temperature TN for BiFeO_(3)-SFS compositions is close to the TN(x)dependence for BiFeO_(3)solid solution with disordered perovskite PbFe_(1/2)Nb_(1/2)O_(3)(PFN).In contrast to this TN(x)dependence for BiFeO_(3)-PFS compositions nicely follows the theoretical TN(x)dependence calculated for the case of the ordered distribution of Fe3+and non-magnetic Sb^(5)+ions in the lattice(chemical ordering).