La-doped and La/Mn-co-doped Barium Titanate Ceramics

Barium titanate ceramics doped with 0.3 mol.% lanthanum and co-doped with 0.3 mol.% lanthanum and 0.05 mol.% manganese were investigated. The powders were prepared by a modified polymeric precursor method based on the Pechini process. The ceramics were obtained by sintering at 1300 degrees C for 8 h. The influence of dopants on structural changes and grain size reduction was analyzed. The presence of dopants influenced the tetragonality of the barium titanate crystal structure. Reduction of polygonal grain size with dopant addition was noticed. In the doped ceramics, characteristic phase transitions were shifted to lower temperatures in comparison with pure barium titanate. The dielectric permittivity value showed the tendency of a slight increase with lanthanum addition and further increase with adding of manganese. La as a single dopant increased the diffuseness of phase transitions indicating the formation of a diffuse ferroelectric material but in the co-doped ceramics the phase transition diffuseness decreased. The resistivity of the co-doped ceramics was higher than for lanthanum doped ceramics, indicating possible segregation of manganese at grain boundaries that influenced the total resistivity of the material

Low frequency noise characteristics of BaTiO3-NiFe2O4 composites at phase transition

In this work we present detailed investigation of low frequency noise characteristics of BaTiO3-NiFe2O4 ceramic composites of different percentage of NiFe2O4. At the particular temperatures (that gets under the broad maximum of dielectric permittivity observed around 300 K) very intensive few separate peaks of random telegraph noise signal were observed. It shows that phase transition in the investigated materials goes through separate stages instead of the smeared out one. Characteristic times of the physical processes during the phase transition are close to one millisecond, and activation energy is around (0,340,49) eV