Search

Physical review / B covering condensed matter and materials physics 100(13), 134104 (2019). doi:10.1103/PhysRevB.100.134104, The structural and dielectric characterization of 30% Sn-doped BaTiO3 (BaSn0.3Ti0.7O3) as a function of temperature is carried out combining, complementary probes to reveal structural modifications associated to the relaxor behavior. Dielectric data confirms the existence of relaxor-type behavior in BaSn0.3Ti0.7O3. The local and average structural changes as a function of temperature have been investigated in the region of broad changes of dielectric response. Local probes, such as x-ray absorption fine structure spectroscopy and Mössbauer spectroscopy reveal a special trend of the lattice related to the diffuse dielectric phase transition as observed from dielectric data. The analysis of Raman spectra as a function of temperature reveals a peculiar behavior in the temperature region corresponding to the dielectric transition. The analysis of x-ray diffraction patterns points out a pseudocubic structure throughout the temperature range while the volume exhibits a negative thermal expansion in the region of broad dielectric maximum. Our results suggest structural modifications occurring in the system throughout a wide temperature range, interestingly, associated with changes in macroscopic properties of relaxors such as dispersion in dielectric constants and raising of dipole moments, Published by Inst., Woodbury, NY

Journal of physics / Condensed matter 31(34), 345403 (2019). doi:10.1088/1361-648X/ab21ee, The present work is aimed at exploring the local atomic structure modifications related to the spin reorientation transition (SRT) in DyFeO$_3$ orthoferrite exploiting x-ray absorption fine structure (XAFS) spectroscopy. For this purpose we studied by XAFS the evolution of the local atomic structure around Fe and Dy as function of temperature (10–300 K) in a DyFeO$_3$ sample having the SRT around 50–100 K. For sake of comparison we studied a YFeO$_3$ sample having no SRT. The analysis of the extended region has revealed an anomalous trend of Fe–O nearest neighbour distribution in DFO revealing (i) a weak but significant compression with increasing temperature above the SRT and (ii) a peculiar behavior of mean square relative displacement (MSRD) [$\sigma^2$] of Fe–O bonds showing an additional static contribution in the low temperature region, below the SRT. These effects are absent in the YFO sample supporting these anomalies related to the SRT. Interestingly the analysis of Dy L$_3$-edge data also reveal anomalies in the Dy–O neighbour distribution associated to the SRT, pointing out a role of magnetic Re ions across $T_{SRT,Fe}$. These results point out micro-structural modification at both Fe and Dy sites associated to the magnetic transitions in DFO, it can be stated in general terms that such local distortions across $Fe^{3+}$ and magnetic Re$^{3+}$ may be present in other orthoferrites exhibiting multiferroic nature., Published by IOP Publ., Bristol