Influence of impurities on the properties of rare-earth-doped barium‐titanate ceramics

Abstract

Investigations of impurity centers, electrical resistivity and microstructure of BaTiO 3 ceramics doped with rareearth ions Y, La, Nd, Sm, Dy and Lu at concentrations x~0.001±0.005 were carried out. Electron paramagnetic resonance, X-ray diffraction and electron microscopy were used for measurements. The most intense EPR lines were shown to belong to paramagnetic complexes Fe 3z ±V O and Ti 3z ±Ln 3z (Ln~rare-earth ion, V O~o xygen vacancy). A change in symmetry of the center Fe 3z ±V O at the transition temperature from the ferroelectric to paraelectric phase has been revealed for the ®rst time. Measurements of the dependence of EPR line intensities and electrical resistivity with rare-earth ion concentrations were performed. The observed correlation in their behaviour showed an essential role of the identi®ed paramagnetic complexes in the appearance of BaTiO 3 ceramic semiconducting properties and the positive temperature coef®cient of resistance (PTCR) effect. The latter effect was at a maximum for x#x c where x c #0.002±0.003 is the critical rare-earth ion concentration which determines the excess charge compensation mechanism. Up to x c , the rare earths investigated, (except for the small ion Lu), substitute for barium, and the main compensation mechanism is an electronic mechanism. At high concentrations (xwx c ) in the case of large ions (e.g. La), substitution is at barium sites, with the creation of titanium vacancies, whereas intermediate ions (e.g. Y) begin to substitute for titanium. The in¯uence of impurities on the BaTiO 3 microstructure, including the grain sizes, is discussed.

Study of Batio_3 Ceramics Doped With Mn and Ce or Nb and Sr

“…Magnetic field (mT) complex Ti 3+ -Ln 3+ (Ln 3+ is a rare-earth ion) [11], while in [12] it was supposed that it belongs to Ti 3+ -V O . Another line in the spectrum has g-factor 5.549.…”

Semi-oxalate synthesis of (1−x)BaTiO3−xM0.5Bi0.5TiO3 (M = Li, Na, K) PTCR materials

“…The starting chemicals used in the preparation of 2 at above 800 ℃ for 2 h. In the second step of the synthesis process, extra-pure M 2 CO 3 (M = Li, Na, K), Bi 2 O 3 , and TiO 2 were added to BaTiO 3 in order to obtain solid solutions (semi-oxalate (SO) method). The powders were mixed by ball milling with ethanol for 4 h. The resultant mixtures were fired for 4 h at temperatures from 800 to 870 ℃.…”

“…Materials with positive temperature coefficient of resistance (PTCR) [1][2][3][4] based on ferroelectrics-semiconductors are of particular interest. These materials are characterized by the presence of semiconductor cores and dielectric boundaries of ceramic grains.…”

[Retracted Article] Performance of Ba_0.95Ca_0.05Zr_0.15Ti_0.85O₃/PVDF composite flexible films

“…To improve the ferroelectric properties, researchers concentrate their attention on the doping of metal ions into BaTiO 3 crystal. 8), 9) Metal oxides-doped BaTiO 3 ceramics have been found to possess a significant improvement in dielectric properties, as well as an interesting dielectric relaxation behavior. Li et al 8) doped a small amount of CuO into BaTiO 3 ceramics, probed into its effect on the microstructures and dielectric properties of BaTiO 3 .…”

“…8), 9) Metal oxides-doped BaTiO 3 ceramics have been found to possess a significant improvement in dielectric properties, as well as an interesting dielectric relaxation behavior. Li et al 8) doped a small amount of CuO into BaTiO 3 ceramics, probed into its effect on the microstructures and dielectric properties of BaTiO 3 . It was discovered that the permittivity increases markedly for CuO dopant content x = 0.2 0.4% and the dielectric loss decreases significantly after being doped by CuO and down to a minimum value for x = 0.8%.…”