57Fe-enriched perovskites M(Fe0.5Nb0.5)O3 (M – Pb, Ba) studied by Mössbauer spectroscopy, NMR and XRD in the wide temperature range 4.2–533 K

The ⁵⁷Fe enriched perovskites Pb(Fe_0.5Nb_0.5)O₃ and Ba(Fe_0.5Nb_0.5)O₃ prepared by a ceramic method were studied by Mössbauer spectroscopy, NMR, conventional and synchrotron XRD. The temperature dependences of hyperfine and structural parameters from 4.2 K to temperatures above the ferroelectric ordering shows the presence of AF magnetic ordering transitions and the spin-glass transition under the Néel temperatures. In PFN sample, the structural change from trigonal to cubic structure around T_N is observed, while the cubic structure is stable in the temperature range from 4.2 K to 530 K for BFN. The Fe/Nb perturbed arrangement was suggested based on results of Mössbauer and NMR spectroscopies.