Valence states and dielectric properties of fine-grained BaTiO3 ceramics co-doped with double valence-variable europium and chromium

Abstract

(Ba1–xEux)(Ti1–xCrx)O3 (x = 0.01‒0.05) (BETC) and (Ba1–xEux)(Ti1.01–xCrx–0.01)O3 (x = 0.02‒0.05) (BETC1) ceramics with single-phase perovskite structures were prepared using a mixed-oxides method. The structure, microstructure, site occupations, valence states of Eu/Cr, and dielectric properties of these ceramics were investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, fluorescence spectroscopy, emission spectroscopy, electron paramagnetic resonance, and dielectric measurements. The mixed valence states of Eu3+/Eu2+ and Cr3+/Cr5+ were confirmed. Co-doping with Eu and Cr greatly inhibited the grain growth of BaTiO3 ceramics, resulting in a fine-grained microstructure (0.7 µm). Two permittivity peaks of BETC with x ≥ 0.02 were characteristic of an inhomogeneous dopant concentration distribution forming a core–shell structure. For BETC1, the mixed valence states and site occupations of Eu/Cr were analyzed to elucidate an expansion in the unit-cell volume, very high Eu/Cr ratio (= 3.5) in coarser grains, regular diffuse phase transition behavior, rapid Tm-shifting rate of − 24 °C/at% (Eu/Cr), higher ε′RT (= 4550), and lower tan δ (= 0.0196) in BETC1, as well as the destruction of the core-shell structure in BETC.