Barium titanate/noble metal laminates prepared by the oxidation of solid metallic precursors
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A novel and attractive method for preparing multicomponent electronic ceramics and ceramic-metal composites is the oxidation of solid metallic precursors (SMP). This metallurgical processing route consists of the following steps: (i) preparation of a solid metallic precursor containing the proper ratio of elements for the final ceramic or ceramic-metal composite, (ii) compaction and forming of the metallic precursor into a desired shape, and (iii) oxidation to produce a monolithic ceramic or ceramic-metal composite. While the SMP method has been used to prepare wires and tapes containing a variety of superconducting oxides, this method has not been widely used to synthesize other electronic ceramics. In this paper, the synthesis of dielectric BaTiO3/noble metal laminates from solid metallic precursors is discussed. Ba-Ti precursor powders have been produced by solid-state mechanical alloying. The precursor powder was sealed inside noble metal tubes and rolled to form thin Ba-Ti/noble metal laminates. Exposure of the Ba-Ti core in such tapes to temperatures s=300 °C in pure oxygen resulted in rapid oxidation. Post-oxidation annealing at elevated temperatures (^900 °C) yielded dielectric BaTiO 3 /Ag or BaTiO 3 /Pd laminates.
I. INTRODUCTION Ceramic-metal composites are used, or are being considered for use, as key components in a variety of advanced electronic devices. Integrated circuit packages and multilayer capacitors are examples of dielectric ceramic/metal laminates that are in widespread use. 1 Multilayer piezoelectric ceramic/metal laminates are also finding increased application in "smart" systems that can sense and respond to environmental changes.2 Multifilamentary superconducting oxide/noble metal wires and tapes are being developed for magnetic levitation (trains, ore separation), magnetic energy storage, electric motors, and magnetic resonance imaging.3"5 Electronic ceramic/noble metal laminates are commonly prepared by blending ceramic or metal powders with organic materials (e.g., an organic binder, plasticizer, solvent, etc.), tape-casting the ceramic-organic mixtures and screen-printing the metal-organic mixtures in alternating layers to form a multilayer green tape, and then firing the tape to burn off the organics and to obtain a dense multilayer component.1 Incomplete or nonuniform pyrolysis of the organic material during firing can result in flawed components (e.g., delaminations, retained carbon, etc.) and/or components of undesired shape.1'6'7 Thus, new processes that do not require the use of organic binders, plasticizers, etc. for producing shaped ceramic components are desired. An alternate method for preparing ceramic/noble metal multilayer composites is the oxidation of metallic 2968
http://journals.cambridge.org
J. Mater. Res., Vol. 8, No. 11, Nov 1993
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precursor/noble metal laminates (see schematic in Fig. I). 8 This solid metallic precursor (SMP) processing route consists of the following steps: (i) preparation of a metallic precursor powder, containing the
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