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X-ray photoelectron spectroscopy was used to study a lead-based relaxor dielectric ceramic to identify the grainboundary 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, and 01s 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 Pb,O, and PbO,. In addition, the broadness of the Pb4fTI2 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 PbO, and PbO. The results strongly supported the resistance degradation mechanism of relaxor dielectric ceramics under humid loading conditions as previously proposed by the authors.

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