Grain-Boundary-Phase Identification of a Lead-Based Relaxor by X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy was used to study a lead-based relaxor dielectric ceramic to identify the grain-boundary phase most likely to be responsible for the insulation degradation of relaxor dielectric ceramics under humid loading conditions. The grain-boundary phase consisted mainly of lead and oxygen. The binding energies of Pb4f7/2 and O1s in the grain-boundary phase were found to be 137.3 eV and 528.8 eV, respectively, and these values agreed well with those for Pb3O4 and PbO2. In addition, the broadness of the Pb4f7/2 peak suggested the presence of PbO. Measurements were made of lead dissolution from dielectric ceramics in hot water; specimens with a grain-boundary phase gave a 30 to 50 times greater lead concentration in the hot water than specimens without a grain-boundary phase. This demonstrated that the grain-boundary phase easily dissolved in hot water. Thus, it was concluded that the grain-boundary phase contained water-soluble PbO2 and PbO. The results strongly supported the resistance degradation mechanism of relaxor dielectric ceramics under humid loading conditions as previously proposed by the authors.