| Micro-Raman and electron nano-probe techniques are used to show that lead zirconate-titanate (PZT) and samarium-doped bismuth titanate undergo local phase transformations during electrical shorting. In PZT dendrite-like shorts of a few microns diameter, produced by extreme bipolar voltage cycling fatigue, are mapped spectroscopically in 1 µm2 areas and exhibit almost pure regions of α-PbO, β-PbO and rutile TiO2. [Note that β-PbO is not the stable ambient phase.] Similarly, the Sm-doped bismuth titanate converts under large dc voltages from layered-perovskite structure to a pyrochlore structure during filamentary electrical breakdown, with the loss of Bi. The results complement the very recent hot luminescence study of J. C. Tsang and B. P. Lindner, Appl. Phys. Lett. 84 (2004) 4641 in related thin-film gate oxides. |
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