Nanostructure Evolution During the Transition of TiO 2 , PbTiO 3 and PZT from GELS to Crystalline thin Films.
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NANOSTRUCTURE EVOLUTION DURING THE TRANSITION OF T10 2 , PbTiO3 AND PZT FROM GELS TO CRYSTALLINE THIN FILMS. Z.C. KANG*+, A. GUPTA#+, M.J MCKELVY+, L. EYRING*+ and S.K. DEY# *Department of Chemistry; +Center for Solid State Science; kChemical, Bio and Materials Engineering Department; Arizona State University, Tempe, AZ 85287 ABSTRACT The nanostructure evolution of PZT, PT and T thin fi]ms has been studied by high-resolution electron microscopy (HREM) supported by other techniques such as thermal analysis, thermal mass spectrometric analysis and X-ray diffraction analysis. The evolution follows a common progression from amorphous film, to the development of condensed regions that develop crystalline order, to the final polycrystalline oxide thin film. If the precursor gel contains lead, the film develops fluctuating surface "blisters" that evolve to an oxide final product as well. Minor structural and compositional differences exist across the final oxide thin film. INTRODUCTION Ferroelectric thin films prepared by sol-gel processing are being paid considerable attention [1]. Processing involves drawing or spinning the thin-film gel followed by heat treatment to produce the crystalline thin, ferroelectric film. It is clearly of fundamental and techno.cgical value to understand the sequence of reactions and transformations that accompany gel to crystalline thin-film processing. A brief report of the nanostructure evolution of a Pb(Zr 0 4 5 Ti 0 55 )03 (PZT) thin-film gel has been made [2]. In this paper a systematic study of the structural evolution from alkoxy gel to PZT, PbTiO 3 (PT) and TiO2 (T) utilizing high-resolution electron microscopy (HREM) together with thermal analysis (TGA and DTA), thermal mass spectrometric analysis (TMSA) and X-ray diffraction (XRD) is reported. EXPERIMENTAL ?ART The preparation procedures of the PZT thin-film gels for HREM studies was similar to that reported previously [2]. rhe specimens fur the other techniques required powders made from dried gel2. The precursor sol for PT was made from lead acetate, and titanium isoprrnpoxide in methoxyethanol. The precursor sol for T was titanium isopropox-de solution. Electron-bean, heating was used to age the thin-film specimens in the microscope. RESULTS AND DISCUSSION The amorphous state of the thin-film gels As previously reported [2], the dipped and quickly dried PZT precursor film is amorphous. The same is true for the PT and T thin films as confirmed by the images and diffraction patterns of Fig. 1. The diffraction patterns all show a broad inner ring corresponding to nearest neighbor distances of 3.03 + 0.03 A and a weak second halo suggesting a continuous random network [3].
Mat. Res. Soc. Symp. Proc. Vol. 230. ,11992 Materials Research Society
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Figure 1. The amorphous state of T, PT and acid- and base-catalyzed PT and PZT.
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All the images shown were taken about 10 minutes after beginning microscopic observation. There is no long-range order. However, if the beam for optical diffraction is small there are imaged regions t
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