Microstructural evolution during pyrolysis of triol-based sol-gel single-layer Pb(Zr 0.53 Ti 0.47 )O 3 thin films
- PDF / 562,787 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 74 Downloads / 180 Views
David Hind, Steven J. Milne, Andy P. Brown, and Rik Brydson Department of Materials, University of Leeds, Leeds LS2 9JT, U.K. (Received 24 January 2002; accepted 28 May 2002)
Advanced analytical transmission electron microscopy has been used to investigate microstructural evolution during pyrolysis in triol-based sol-gel thin films. At pyrolysis temperatures up to 300 °C, the films remained amorphous; however, nanometer-sized precipitates were observed in films heat-treated up to 400 °C for 10 min. Analytical transmission electron microscopy indicated that the precipitates were Pb-rich, as well as deficient in O, Ti, and Zr. Films pyrolyzed up to 500 °C for 10 min were composed of a nanocrystalline pyrochlore phase; however, pores could be observed, situated in the same position as the nanometer-sized precipitates at 400 °C. Face-centered cubic Pb-rich crystallites were also present on the surface of pyrolyzed films but absent in the fully crystallized films annealed at 650 °C. A tentative mechanism is proposed to explain these observations.
I. INTRODUCTION
Lead zirconate titanate (PZT) thin films have been widely investigated for use as nonvolatile memories, thermal imaging arrays, and piezoelectric micro- or nanoactuators.1,2 Sol-gel techniques have been used extensively for the preparation of PZT thin films due to advantages such as high purity, ease of compositional control, low processing temperature, and low capital cost.3,4 Sol-gel processing of PZT thin films usually involves coating using a solution precursor and pyrolysis of the dried gel at approximately 400 °C, followed by crystallization of the layers by annealing at between 500 and 700 °C. Pyrolysis is an important and complicated step transforming amorphous metalorganic precursors into inorganic glassy materials, ready for crystallization. In PZT gels, differential thermal analysis shows exothermic peaks between 400 and 500 °C due to combustion of organics.5–7 It has been reported that PZT gel samples prepared in methoxyethanol often exhibit a black color in the temperature range 250–500 °C, resulting from the formation of carbon residues, which may be prevented by steam treatment of the dried gels at 300 °C.6 Some authors have found elemental Pb from the reduction of Pb2+ by organic residues during pyrolysis, particularly when samples are rapidly heated to 400 °C.8,9 However, the formation of Pb (and PbO) destroys the homogeneous
a)
Address all correspondence to this author. e-mail: [email protected]
2066
http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 8, Aug 2002
Downloaded: 15 Mar 2015
distribution of all components in the amorphous PZT, contradicting the aim of sol-gel processing which is to have an intimate, homogeneous mix of all elements prior to crystallization. A triol-based sol-gel route has been recently devised by Milne et al.,7,10 which is capable of producing crackfree single layer films of up to 500-nm thick. However, pores and formation of second phases remain a problem in films 艌100 nm.11 This work chara
Data Loading...
