Effects of La_2O_3 and Nb_2O_5 doping on the dielectric properties of Ba_(0.9)Sr_(0.1)TiO_3 ceramics

摘要

Ba_(0.9)Sr_(0.1)TiO_3 ferroelectric ceramics with dopants of La_2O_3(0, 0.1, 0.1, 0.2 mol%) and Nb_2O_5(0, 0, 0.1, 0.1 mol%) were prepared in solid state process. The double donor substitutions can weaken lattice size effect by the two different size substitutions. XRD method was used to analyze the crystal structure of the samples, and SEM was used to observe the topography, grain's size and ceramics density. The results of dielectric-frequency relation indicate that when the contents of La_2O_3 and Nb_2O_5 are both 0.10 mol%, the permittivity can reach to 150 000, and the dielectric loss keeps only 0.118. When the total donor content is lower than 0.40 mol%, compensation effect is dominated by electrons. The giant permittivity is attributed to electrons inside grain and insulated grain boundary. When the dopant content is higher than 0.40 mol%, the compensation effect is dominated by the host cation vacancies. The permittivity decreases rapidly with the increase of the donor concentration.