Dielectric Properties in Transition Metal and Rare‐Earth‐Doped Multiferroic BaTiO 3 Nanoparticles

The temperature, doping concentration, size, and magnetic field dependences of the real part of the dielectric function ϵ ′ for Fe and Er ion‐doped BaTiO 3 bulk and nanoparticles—are calculated using microscopic models and the Green's function technique. The Fe ions substitute the Ti ions and cause a tensile strain. The maximum value of ϵ ′ and the ferroelectric phase transition temperature T C decrease with increasing the Fe doping concentration. Moreover, ϵ ′ decreases with decreasing particle size and increases with increasing an external magnetic field. The latter is an evidence for a strong magnetodielectric effect. By substituting the Ba with Er ions, there appears a strong compressive strain. It causes an increase in the maximum of ϵ ′ and T C with increasing the Er ion concentration.