Dielectric properties and defect chemistry of barium titanate ceramics co-doped R and Dy ions (R=Eu, Gd, Tb)

The structure, microstructure, dielectric behavior, point defects, mixed valence states, site occupations, and defect chemistry of nominal (Ba1-xRx)(Ti1-x,Dy-x)O-3 (x=0.06, R=Eu, Gd, Tb) (BRTD) ceramics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, electron paramagnetic resonance (EPR), dielectric and resistivity measurements. BRTD exhibited a tetragonal perovskite structure, a higher ceramic density of rho(r)=91% of theoretical density, a diffuse phase transition (DPT) behavior, and a nonlinear shift in dielectric-peak temperature (T-m) with the kind of doping ions. The feature of mixed valence states associated with site occupation is responsible for this abnormal T-m-shiftrate. BRTD with R=Tb exhibited a lowest dielectric loss of tan delta=0.025 at 1 kHz and a nearly frequency-independent stability up to 10(7) Hz at room temperature. A double-site compensation mode of Gd-Ba(center dot)-Dy'(Tl), could be formed and led to a rapid T-m-shift rate of approximately-10 degrees C/%(Gd-Dy). A symmetrical EPR signal at g=1.985 was designated as Gd3+ (4f(7)) Kramers ions. The mixed valence states of Ba-site Eu3+/Eu2+ (4f(7)) and Ba-site Tb3+/Ti-site Tb4+ (4f(7)) appeared in BRTD owing to the metastable nature of the 4f(7) electron configuration. The Raman spectra in a high-wavenumber region of 1500-6700 cm(-1) were discovered and might be likely linked to the 4f(7) doping ions, such as Eu2+, Gd3+, and Tb4+ ions. The defect chemistry is discussed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.