Browsing by Author "Kwok, C. K."

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    Novel Method For Determining The Curie-Temperature Of Ferroelectric-Films
    Kwok, C. K.; Desu, Seshu B. (AIP Publishing, 1993-09-01)
    A novel technique to measure the Curie temperature of ferroelectric thin films has been developed. The method is based on identifying changes in slope of film stress versus temperature plot. At the Curie temperature, ferroelectric films undergo a phase transition from ferroelectric phase to paraelectric phase. Due to this phase transformation, physical properties of films such as elastic constants and coefficients of thermal expansion also change at the Curie temperature. Consequently, at this temperature the temperature coefficient of film stress changes since it is related to elastic constants and thermal expansion coefficient. Thus, by measuring the film stress as a function of temperature, the Curie temperature can be determined. The Curie temperatures measured by this method are in good agreement with the literature values. Small discrepancies that were observed can be attributed to the intrinsic stresses present in the films.
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    Pyrochlore to Perovskite phase-transformation in sol-gel derived lead-zirconate-titanate thin-films
    Kwok, C. K.; Desu, Seshu B. (AIP Publishing, 1992-03-01)
    Pyrochlore to perovskite phase transformation in sol-gel derived lead-zirconate-titanate (PZT) films was studied by x-ray diffraction and transmission-electron microscopy (TEM). X-ray diffraction studies of PZT films on sapphire substrates indicated that the pyrochlore to perovskite phase transformation was completed at 650-degrees-C. In contrast, TEM investigations of free-standing PZT films showed that the phase transformation was completed at much higher temperatures. This discrepancy in the behavior of free-standing films versus films on substrate can be related to the size effect.