Phase separation in lead zirconate titanate and bismuth titanate during electrical shorting and fatigue

Micro-Raman and electron microprobe techniques are used to show that lead zirconate titanate and samarium-doped bismuth titanate undergo local phase transformations and separation during electrical shorting and in the dendritic precursors to microshorts caused by bipolar fatigue. These precursors for shorts, consisting of dark filaments, were studied just before they completely shorted the sample. The aim of the study was to compare electrical breakdown and breakdown precursors in AB O3 perovskite oxides and related Aurivillius phase layer structures with Bi (A site) substitution and with B -site substitution (e.g., Ti for Zr in PZT). The observation of phase separation and decomposition is related to congruent and incongruent meltings in these materials. Dendritelike shorts and short precursors of a few microns in diameter, produced by extreme bipolar voltage cycling fatigue, are mapped spectroscopically in 1 μ m2 areas and exhibit almost pure regions of α-PbO, Β-PbO, and rutile TiO2. The α-Β PbO phase boundary runs from 500 °C at 1 atm to room temperature at 0.4 GPa, easily accessible temperatures and pressures in the dynamical process. Similarly, under large dc voltages the Sm-doped bismuth titanate transforms from a layered-perovskite structure to a pyrochlore structure during filamentary electrical breakdown, with the loss of Bi. The interfacial phase separation has been attributed to the combination of defect aggregation and thermal decomposition effects.