Impact of quenched random fields on the ferroelectric-to-relaxor crossover in the solid solution (1−x)BaTiO3−xDyFeO3<

Abstract

Lead-based perovskite relaxor ferroelectrics are widely used as materials for numerous applications due to their extraordinary dielectric, piezoelectric and electrostrictive properties. While the mechanisms of relaxor behavior are disputable, the importance of quenched (static) random electric fields created at nanoscale by the disordered heterovalent cations has been well recognized. Meanwhile, an increasing amount of scientific and technological efforts have been concentrated on lead-free perovskites, in particular, solid solutions of classical ferroelectric BaTiO 3 (BT), which better meet ecological requirements. Among BT-based solutions the homovalent systems are elaborately studied where strong random electric fields are absent, while the solubility limit of heterovalent solutions is typically too low to fully reveal the peculiarities of relaxor behavior. In this work, we prepared a new perovskite solid solution system (1-x)Ba 2+ Ti 4+ O 3-xDy 3+ Fe 3+ O 3 (0 ≤ x ≤ 0.3) and studied it as a model heterovalent lead-free system. We determined crystal structure, ferroelectric and 2 dielectric properties of ceramics in a wide range of temperatures and concentrations, constructed phase diagram, found and analyzed the concentration-induced crossover from normal ferroelectric to relaxor behavior. We demonstrated that quenched random electric fields of moderate strength promote the ferroelectric-to-relaxor crossover, but do not change qualitatively the peculiarities of relaxor behavior, while strong enough fields destroy the relaxor state, so that the material becomes an ordinary linear dielectric. The experimental results are compared with the predictions of known theories of relaxor ferroelectricity.

Rare Earth Orthoferrite Tuning of Transmitted Waves as Natural Metamaterials

“…Rare earth orthoferrites are a model system to study the nature of iron spins in correlated electron systems. , When the temperature is lowered below the Néel temperature, iron spins begin to order antiferromagnetically and interact strongly. ,− Rare earth orthoferrites have a distorted perovskite structure with an FeO 6 octahedron tilt angle. This slight distortion, which causes an antiferromagnetic moment from the unstrict antiparallel arrangement, results in a weak ferromagnetic moment. − Coupling between spin subsystems produces a variety of complex and interesting phenomena. ,− Spin reorientation transitions and the excitation of ferromagnetic and antiferromagnetic resonances have been observed by experimentally collecting and analyzing electromagnetic pulses. − Frequency shifts have been observed upon lowering the temperature because of changes in the anisotropic energy. ,,, Frequency shifts of antiferromagnetic and ferromagnetic resonances in the spin reorientation transition process of single crystal NdFeO 3 have been reported . Frequency shifts during the cooling of TbFeO 3 , TmFeO 3 , and HoFeO 3 ceramics have also been reported. − These results obtained by using terahertz (THz) waves to excite intrinsic resonances and observations of the frequency shifts during spin reorientations show that temperature engineering can be used to tune the responses of rare earth orthoferrites.…”