Enhanced ferroelectric relaxor behavior of Ho₂O₃-modified barium zirconate titanate ceramics

Ho₂O₃ doped Ba(Zr_0.1Ti_0.9)O₃ ceramics were prepared by conventional solid state reaction route and their microstructure, dielectric properties and ferroelectric properties were investigated with the variation of Ho₂O₃ content using X-ray diffraction, scanning electron microscope, LCR measuring system and ferroelectric tester. It is found that the Ho³⁺ ions initially substitute the B-site host ions maintaining the perovskite structure in Ba(Zr_0.1Ti_0.9)O₃ ceramics and then contribute to the formation of secondary phase with the continuous increase of Ho₂O₃ content. The average grain size decreases significantly as the Ho₂O₃ concentration increases. The ferroelectric-paraelectric phase transition temperature T_m of Ba(Zr_0.1Ti_0.9)O₃ ceramics decreases with increasing Ho₂O₃ content. Based on the increase of critical exponent γ from the modified Curie–Weiss equation as well as the increase of deviation from Curie–Weiss law, the diffuse phase transition behavior is enhanced with increasing Ho₂O₃ content, indicating a composition-induced diffuse transition. A normal ferroelectric behavior with diffuse phase transition is obtained for the undoped Ba(Zr_0.1Ti_0.9)O₃ ceramics. However, the relaxor-like ferroelectric behavior with a strong frequency dispersion of relative permittivity maximum ε_rmax at T < T_m and a strong diffuse phase transition is found for Ba(Zr_0.1Ti_0.9)O₃ ceramics with high Ho₂O₃ content. The high Ho₂O₃ content ceramics obey the empirical Vogel–Fulcher relation, which confirms the relaxor behavior of Ba(Zr_0.1Ti_0.9)O₃ ceramics with high Ho₂O₃ content. The remnant polarization increases and then decreases with the increasing Ho₂O₃ content while the coercive field decreases with the increase of Ho₂O₃ content in Ba(Zr_0.1Ti_0.9)O₃ ceramics.