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
Abstrakt
The 57Fe enriched almost single-phase perovskites Pb(Fe0.5Nb0.5)O3 (PFN) and Ba(Fe0.5Nb0.5)O3 (BFN), prepared by a ceramic method (solid-state synthesis), were studied by Mössbauer spectroscopy, nuclear magnetic resonance (NMR), conventional and synchrotron X-ray powder diffraction (XRD). The temperature dependences of hyperfine and structural parameters of PFN, BFN from 4.2 K to temperatures above ferroelectric ordering of PFN (TS~375 K), with attention to the values of magnetic and structural transitions, were obtained.
The antiferromagnetic magnetic ordering transitions were found under the Néel temperatures TN~167(3) K and 32(2) K for PFN and BFN, respectively. The spin-glass transition was at TG~10(3) K and 20(5) K for PFN and BFN, respectively.
In PFN sample a small change of structural parameters around TN and structural change from trigonal to cubic structure at TTILDE OPERATOR+D91400 K was observed by XRD. The temperature dependence of XRD shows stable cubic structure in the temperature range from 4.2 K to 530 K for BFN.
From Mössbauer and NMR spectroscopies it is found that both structures have perturbed environments for Nb and Fe. However, in case of PFN the low values of transferred hyperfine fields disfavour random Fe/Nb arrangement and allow proposing a picture of Fe/Nb arrangement.