Thick-Film Processing of Pb 5 Ge 3 O 11 -Based Ferroelectric Glass-Ceramics
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ABSTRACT Processing techniques were investigated to produce c-axis orientation, or texture, of ferroelectric PbGe3O1l-based glass-ceramic compositions during crystallization of amorphous thickfilm printed samples from the Pb 5GCe 3 OI-PbTiO3 (PG-PT) and Pb5Ge3O11-Pb(Zr1,2TYi2)O 3 (PG-PZT) systems. In these systems the PG crystallized into a ferroelectric phase, producing a multiple ferroelectric phase composite at low temperatures, PG-PT or PG-PZT. In this way the nonferroelectric component of traditional ferroelectric glass-ceramics was eliminated. INTRODUCTION Ferroelectric glass-ceramics consist of a crystallized ferroelectric phase in a non-ferroelectric residual glass matrix. In this type of microstructure the connectivity of the ferroelectric phase is limited. Thus, electrical poling is difficult, preventing the development of piezo- and pyroelectricity. Lead germanate, PbGe3 O11 (PG), was selected because it is a unique ferroelectric which can be formed into a glass relatively easily. In addition, PG has a low melting temperature of 738"C [1] and, thus, has been extensively investigated as a liquid phase sintering aid to lower the processing temperatures of ferroelectric ceramics [2-15]. Lead germanate is of interest for pyroelectric applications [16-19] because of the combination of a relatively high pyroelectric coefficient with low dielectric constant and loss. However, the processing conditions to form PG as a polycrystalline solid are not well developed, especially in film form (thick or thin). A variety of processing problems have been encountered in previous research as well as in this research. However, by optimizing the processing conditions, primarily in thick-film form, unique pyroelectric properties may be achieved from orientation or texture of the microstructure at low processing temperatures [19]. The purpose of this research is to establish the potential for utilizing lead germanate as the glass forming component in ferroelectric glass-ceramics containing PT or PZT, and to develop improved methods of processing PG-based compositions for pyroelectric applications. The focus of this paper is centered on the (1) processing techniques that produce c-axis orientation of PG-based ferroelectric glass-ceramic compositions, (2) crystallization behavior of the screen-printed thick-films, and (3) effects of A120 3 and MgO substrates on the formation of the investigated compositions. EXPERIMENTAL PROCEDURE Amorphous compositions were prepared by melting and rapidly quenching PG-based materials in a counter-rotating twin steel-roller quenching apparatus to produce amorphous ribbon and ballmilled amorphous powder. The powders were then further processed by pressing bulk samples, or screen- printing thick-films. The samples were heat-treated to densify and crystallize the compositions, followed by characterization with x-ray difitaction (XRD), scanning electron microscopy (SEM) and electrical measurements. Additional details of this procedure are described elsewhere [13, 19-21]. The thick-films
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