Elastic and magnetoelastic relaxation behaviour of multiferroic (ferromagnetic + ferroelectric + ferroelastic) Pb(Fe0.5Nb0.5)O3 perovskite

摘要: Resonant Ultrasound Spectroscopy has been used to characterize elastic and anelastic anomalies in a polycrystalline sample of multiferroic Pb(Fe0.5Nb0.5)O3 (PFN). Elastic softening begins at ~550 K, which is close the Burns temperature marking development dynamical polar nanoregions. A small increase acoustic loss ~425 K coincides with value T* reported for nanoregions starting acquire static or quasi-static component. Softening shear modulus by ~30–35% through ~395–320 K, together peak loss, due classical strain/order parameter coupling cubic → tetragonal → monoclinic transition sequence ferroelectric/ferroelastic transitions. plateau high below ~320 K mobility under stress ferroelastic microstructure but, instead typical effects freezing twin wall motion some low temperature, there steady decrease stiffness ~85 K. This attributed succession strain-coupled defects range relaxation times consistent report literature that PFN develops tweed over wide interval. No overt anomaly was observed near expected Neel point, ~145 K, weak/absent spin/lattice but heat capacity measurements showed antiferromagnetic actually smeared out suppressed. Instead, weakly ferromagnetic up ~560 K, though it not possible exclude definitively possibility this could be magnetic impurity. Overall, evidence from RUS data permeating influence dynamic strain are local heterogeneity on mesoscopic length scale. These, turn, must have role determining properties character PFN.