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Defect Characterization of Pyroelectric Materials

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Final technical rept.

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Two methods for identify point defects applicable to the study of technologically relevant pyroelectric oxide materials have been investigated, namely Positron Annihilation Lifetime Spectroscopy PALS and Electron Paramagnetic Resonance EPR. For this study a PALS spectrometer was constructed. Preliminary PALS and EPR results on powder and ceramic materials are presented. An operational positron annihilation lifetime spectrometer has been constructed and tested. The resolution function width of approximately 205 ps with a count rate of 130 counts S-1 from a 370 kBq-1 source was achieved. Two independent analysis algorithms were tested using simulated lifetime spectra. Systematic studies were performed on a series of polycrystalline pure metal samples. This work confirmed the need for accurate source annihilation correction and allowed a methodology to be developed. Further, this procedure allowed the variation in backscatter source contribution with atomic number to be studied. The spectrometer was then used to study two pyroelectric Pb based perovskite oxide ceramic samples, a La doped PZT sample, Pb,LaZr,TiO3, and an undoped PbSc0.5,Ta0.5O3 PST sample. Fits using maximum entropy method and source corrected fitting using non-linear least square where found to be similar. A second vacancy defect contribution was clearly observed in both samples. Electron paramagnetic resonance measurements were extended from earlier single crystal PbTiO3 work to powder PbZr,TiO3 samples. A series of Mn doped samples was studied. The spectrum was found to contain contributions from both Mn4 and Mn2 charge states.

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  • Statistics and Probability
  • Electricity and Magnetism

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