Accession Number : ADA322576

Title :   Synthesis of Ceramics from Solutions: Functionally Graded Composites, NanoComposites and Single Crystal Thin Films.

Descriptive Note : Technical rept. no. 1 Dec 95-Nov 96,

Corporate Author : CALIFORNIA UNIV SANTA BARBARA COLL OF ENGINEERING

Personal Author(s) : Polli, Andrew D. ; Lange, Fred F. ; Levi, Carlos G.

PDF Url : ADA322576

Report Date : 28 FEB 1997

Pagination or Media Count : 34

Abstract : The crystallization, transformation, and partitioning of amorphous PbO-ZrO2-TiO2 powders produced by pyrolytic decomposition of mixed alkoxide precursors were investigated. Materials have the general formulation Pb1+xTi1/(1+PHI)ZrPHI/(1+PHI)O3+x, where -0.2<= x <= 0.2 is the fraction PbO excess/deficiency and 0 <= phi <= 1 is the Zr/Ti molar ratio. Most compositions first crystallized as a metastable fluorite structure with varying degrees of pyrochlore-like cation ordering, which transformed to a single perovskite phase upon additional heat treatment. Higher Zr/Ti ratios enhanced the retention of fluorite and reduced the incidence of cation ordering. Compositions with off-stoichiometric amounts of PbO often yielded extended solid solutions prior to partitioning. For example, metastable perovskites with as much as 20% PbO deficiency (x = -0.2) could be prepared for 0 <= phi <= 1, but only ^10% PbO excess could be incorporated in solution for 0.33 <= phi <= 1. Increasing PbO content was found to promote crystallization, suggesting that this oxide acts as a network modifier enhancing mobility within the initial amorphous precursor powder. Higher PbO was also noted to favor cation ordering in the metastable phase and to accelerate the transformation to perovskite, as well as to promote partitioning for hyperstoichiometric compositions. The findings are discussed in light of structural relationships between the fluorite, pyrochlore and perovskite phases, as well as current understanding of the thermodynamics of the system.

Descriptors :   *COMPOSITE MATERIALS, *THIN FILMS, *SINGLE CRYSTALS, *CERAMIC MATERIALS, *ZIRCONIUM OXIDES, *TITANIUM OXIDES, *PEROVSKITES, *LEAD OXIDES, SOLUTIONS(MIXTURES), SYNTHESIS, STRUCTURAL PROPERTIES, THERMODYNAMICS, POWDERS, PRECURSORS, LIGHT, AMORPHOUS MATERIALS, CRYSTALLIZATION, PHASE, HEAT TREATMENT, DECOMPOSITION, SOLID SOLUTIONS, METASTABLE STATE, PYROLYSIS, TRANSFORMATIONS.

Subject Categories : Inorganic Chemistry
      Geology, Geochemistry and Mineralogy
      Ceramics, Refractories and Glass
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE