Evidence of magnetoelectric coupling in 0.9BiFeO3-0.1Ba[Ti0.95(Yb0.5Nb0.5)0.05]O3 ceramic

Abstract

The physical properties of the Multiferroïc lead-free 0.9BiFeO3-0.1Ba[Ti0.95(Yb0.5Nb0.5)0.05]O3 ceramic were investigated by in-situ Mössbauer spectroscopy, X-ray diffraction (XRD), dielectric measurements and Raman scattering. Both BiFeO3 and 0.9BiFeO3-0.1Ba[Ti0.95(Yb0.5Nb0.5)0.05]O3 ceramics underwent in-situ Mössbauer spectroscopy in the temperature range of 300 K to 653 K and the parameters of hyperfine interactions were determined. The magnetic transition temperature TN of our doped sample was of 568 K, which was lower than that of BiFeO3. This reduction of TN originated from the presence of different exchange constants resulting from the weakening of JFe-Fe. The deviation of the reduced magnetic hyperfine field H(T)/H(0) as a function of the reduced temperature T/TN from the Brillouin curve of Fe3+ (S = 5/2) for the three sextets and the determination of the critical exponent β, of 0.375 ± 0.022 in the range of 0.01 < 1-T/TN < 0.5 revealed a 3D magnetic long range order phase transition. The complexity of the spatial spin structure was a result of the canting of antiferromagnetically ordered spins of BiFeO3. Our findings revealed the effect of the non-magnetic substituents Ba and Yb/Nb/Ti in A and B sites, respectively on the magnetic properties. Around the magnetic transition temperature, both isomer shift evolution and quadruple splitting distribution showed pronounced anomalies associated with the onset of magnetic ordering. The Debye temperature (θD) was deduced to be of 257 ± 21 K. These results revealed 0.9BiFeO3-0.1Ba[Ti0.95(Yb0.5Nb0.5)0.05]O3 as a promising material for piezoelectric devices. XRD analyses were performed for temperatures from 300 K up to 750 K. Gradual structural evolution, as temperature increased, exhibited an isostructural phase transition and an anomaly in the evolution of lattice parameters and the unit cell volume as well as a significant shift in the atomic positions near the magnetic transition temperature TN. These behaviors indicate magnetoelastic coupling. The temperature dependence of the real part of dielectric permittivity and dielectric loss (tan δ) was investigated over a wide range of temperatures at 1 kHz. During its evolution, an anomaly was observed at 568 K; which corresponded to the magnetic transition temperature TN. Raman scattering spectra were measured in the temperature range from 303 K to 728 K. Drastic changes, especially that of the three two-phonon modes centered at around 1000-1500 cm−1, were the results of magnetic rearrangement and atomic displacement leading to both modulating magnetic exchange interaction and polarization state. All these results prove the magnetoelectric coupling of 0.9BiFeO3-0.1Ba[Ti0.95(Yb0.5Nb0.5)0.05]O3 ceramic.