Extended x-ray absorption fine structure determination of local structure in sol-gel-derived lead titanate, lead zircona
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Extended x-ray absorption fine structure determination of local structure in sol-gel-derived lead titanate, lead zirconate, and lead zirconate titanate S.S. Sengupta, L. Ma, D. L. Adler, and D. A. Payne Department of Materials Science and Engineering, Seitz Materials Research Laboratory, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (Received 14 March 1994; accepted 17 February 1995) We report on extended x-ray absorption fine structure (EXAFS) measurements for partially heat-treated gels in the lead zirconate titanate system (PZT). Self-consistent results obtained from the titanium and zirconium A"-edges and the lead Lm-edge were used to determine bonding pathways between cations. For lead titantate (PT) and PZT gels, separate networks of predominantly Ti-O-Ti, Zr-O-Zr, and P b - O - P b linkages were observed. For lead zirconate (PZ) gels, both Zr-O-Pb and Z r - O - Z r linkages were observed. The results indicate heterogeneity at the molecular level. These findings are discussed in terms of the evolution of structure for PZT materials prepared by our sol-gel method.
The versatility of the sol-gel synthesis method for mixed oxide compositions has led to the preparation of ceramic materials at greatly reduced temperatures.1 For example, materials in the Pb(Zri_xTix)O3 (PZT) system have been integrated on semiconductors by solgel processing and are currently under investigation for nonvolatile-memories, electro-optic modulators, and decoupling capacitors.2'3 In the as-deposited state, the sol-gel-derived thin layers are amorphous, and postdeposition heat treatment is required for densification and crystallization into the perovskite structure. A study of the evolution of structure during heat treatment of amorphous gels should provide a deeper understanding of how local order and coordination influences the subsequent lowtemperature crystallization of chemically derived sol-gel materials. In particular, we are interested in how the structure of the amorphous precursor may affect the ability to densify and crystallize materials at low temperatures. EXAFS is a sensitive structural probe that can be used to determine the local geometry and chemistry in disordered or amorphous materials. EXAFS can, in principle, be used to identify the coordination, type, and bond distance for nearest and higher-order neighbors ("shells") around a specific atom in virtually any solid material.4"7 EXAFS has been used effectively to study many disordered, even liquid, systems, including silica gels and doped fluorite structures.5"11 Despite its obvious applicability, reports on EXAFS for sol-gelderived heterometallic oxide systems have been relatively scarce.12'13 For PZT compounds, the local structure obtained from the different metal atoms can be used to provide a self-consistent picture of the entire local structure of the material. In particular, no study has presented information obtained from all three metal edges in these compounds. J. Mater. Res., Vol. 10, No. 6, Jun 1995 http://journa
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