Structural and dielectric properties of nickel-doped and lanthanum-chromium-doped barium titanate ceramics

Nickel-doped BaTiO₃ (BaTi_1-xNi_yO _3-δ: BTN) and lanthanum-chromium double-doped BaTiO₃ (Ba_1-xLa_xTi_1-xCr_xO₃: BLTC) ceramics were synthesized and their symmetry and dielectric properties were studied. Samples were sintered at 1400°C in air from stoichiometric amounts of BaCO₃ and other metal oxides. X-ray diffraction data were obtained at 20°C. Dielectric properties were measured in the temperature range of 78 K to 453 K. With the increase of dopant ratio y, Curie temperature T_C of BTN decreases, but when y exceeds about 0.01, a hexagonal phase appears and the dielectric constant becomes smaller. On the other hand, in the entire range of x, BLTC shows a perovskite structure and the compounds with larger x exhibit conductive rhombohedral or orthorhombic phases. In the range of x smaller than 0.1, BLTC shows a diffuse phase transition and a high dielectric constant with small tan δ. The relaxor-like frequency dispersion was observed in BLTC at low temperatures.