Dopant distribution and grain growth control in BaTiO3 ceramics doped with ZnO-SiO2-P2O5

In the present work, high-density BaTiO3 ceramics with homogeneous fine-grained microstructure have been obtained by incorporating small amounts of SiO2, P2O5 and ZnO and sintering at temperatures between 1175 and 1225 degrees C. Dilatometry and porosimetry tests showed that sintering starts at higher temperature (around 200 degrees C higher) for the doped material. As a consequence, for the doped material porosity coalescence and removal is promoted while grained growth is inhibited during the first sintering step. SEM and TEM analysis did not reveal any secondary phases in the microstructure of the samples sintered below 1250 degrees C. Grain growth control and microstructural homogeneity seem related to the dopant distribution. XPS analysis showed that the dopants are distributed on the surface of the BaTiO3 particles before the temperature at which sintering starts is reached. The behaviour of the Curie temperature indicates that dopants are incorporated as a solid solution after sintering below 1250 degrees C. this incorporation may lead to compositional changes at the grain boundaries which would be the origin of the lower AC grain boundary which would be the origin of the lower AC grain boundary conductivity measured by complex impedance analysis nd the observed low dielectric losses (well below 1%) of the doped samples. The dielectric characteristics of the doped materials, and the flat dependence of the permittivity with the temperature, make these materials very promising ones for X7R applications. (C) 1997 Elsevier Science Limited.