La/Mn codoped BaTiO3 ceramics with various La2O3 content, ranging from 0.3 to 1.0 at% La, were investigated regarding their microstructure and dielectric properties. The content of MnO2 was kept constant at 0.01 at% Mn in all samples. La/Mn codoped and undoped BaTiO3 were obtained by a modified Pechini method and sintered in air at 13000C for two hours. The homogeneous and completely fine-grained microstructure with average grain size from 0.5 to 1.5mm was observed in samples doped with 0.3 at% La. In high doped samples, apart from the fine grained matrix, the appearance of local area with secondary abnormal grains was observed. The dielectric properties were investigated as a function of frequency and temperature. The dielectric permittivity of the doped BaTiO3 was in the range of 3945 to 12846 and decreased with an increase of the additive content. The highest value for the dielectric constant at room temperature (er= 12846) and at the Curie temperature (er= 17738) were measured for the 0.3 at% La doped samples. The dissipation factor ranged from 0.07 to 0.62. The Curie constant (C), Curie-Weiss temperature (T0) and critical exponent (g) were calculated using the Curie-Weiss and the modified Curie-Weiss law. The highest values of Curie constant (C=3.27?105 K) was measured in the 1.0 at% La doped samples. The obtained values for g ranged from 1.04 to 1.5, which pointed out the sharp phase transformation from the ferroelectric to the paraelectric phase.

Doped BaTiO3-ceramics is very interesting for their application as PTCR resistors, multilayer ceramic capacitors, thermal sensors etc. Ho doped BaTiO3 ceramics, with different Ho2O3 content, ranging from 0.01 to 1.0 wt% Ho, were investigated regarding their microstructural and dielectric characteristics. The samples were prepared by the conventional solid state reaction and sintered at 1320? and 1380?C in an air atmosphere for 4 hours. The grain size and microstructure characteristics for various samples and their phase composition was carried out using a scanning electron microscope (SEM) equipped with EDS system. SEM analysis of Ho/BaTiO3 doped ceramics showed that in samples doped with a rare-earth ions low level, the grain size ranged from 20-30?m, while with the higher dopant concentration the abnormal grain growth is inhibited and the grain size ranged between 2- 10?m. Dielectric measurements were carried out as a function of temperature up to 180?C. The low doped samples sintered at 1380?C, display the high value of dielectric permittivity at room temperature, 2400 for 0.01Ho/BaTiO3. A nearly flat permittivity-response was obtained in specimens with higher additive content. Using a Curie-Weiss low and modified Curie-Weiss low the Curie constant (C), Curie temperature (Tc) and a critical exponent of nonlinearity (?) were calculated. The obtained value of ? pointed out that the specimens have almost sharp phase transition.

This paper examined the microstructural and dielectric characteristics of BaTiO3 - based ceramics of the general formula BaTi1-x-yNbxMnyO3. The concentration of Mn as acceptor was variable 0.01 and 0.05 at%, while the donor (Nb) was fixed at 0.5 at%. The starting ceramic powders were produced by a conventional solid-state reaction method and sintered at 1290 and 1320oC. In BaTiO3 ceramics doped with a higher Mn concentration (0.05 at% Mn) at a sintering temperature of 1290?C, a bimodal structure with a grain of 10-30 ?m, and 1-5 ?m, was obtained. Sintering at a higher temperature (Tsin = 1320?C), regardless of Mn content, provides the achievement of a uniform microstructure with grains under than 6 ?m. The ceramics doped with 0.01 at% Mn and sintered at 1320?C are characterized by high values of the dielectric constant at room temperature and notable changes in the dielectric constant with temperature. Nb-0.05Mn BaTiO3 doped ceramics sintered at 1290?C show lower dielectric constant values due to the presence of Mn-enriched areas representing paraelectric regions. Areas richer in Mn are associated with the fine-grained structure. The dielectric constant in the investigated systems achieves a constant value for frequencies higher than 3kHz. The Curie temperature of all samples was shifted to lower values in relation to undoped BaTiO3 ceramics. According to Curie-Weiss law were determined the Curie constant C and the Curie temperature Tc.