2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session W5: Functional Ceramics: the Nano/Microstructure-Property Relationship in Electronic, Optical, Biological and Structural Materials
2:30 PM–5:30 PM,
Thursday, March 24, 2005
LACC
Room: 502B
Sponsoring
Unit:
FIAP
Chair: Robert Marzke, Arizona State University
Abstract ID: BAPS.2005.MAR.W5.2
Abstract: W5.00002 : Metastable Phase Evolution in Oxide Systems
3:06 PM–3:42 PM
Preview Abstract
Abstract
Author:
Carlos G. Levi
(Materials Department, University of California, Santa Barbara)
Multi-component ceramics are often synthesized by routes that
facilitate mixing at the molecular scale and subsequently
generate a solid product at low homologous temperatures.
Examples include chemical and physical vapor deposition, thermal
spray, and pyrolytic decomposition of precursor solutions. In
these processes the solid evolves rapidly from a highly energized
state, typically in a temperature regime wherein long-range
diffusion is largely constrained and the equilibrium
configuration can be kinetically suppressed. The resulting
product may exhibit various forms of metastability such as
amorphization, nanocrystallinity, extended solid solubility and
alternate crystalline forms. The approach allows access to novel
combinations of structure and composition with unprecedented
defect structures that, if reasonably durable, could have
properties of potential technological interest.
Understanding phase selection and evolution is facilitated by
having a suitable reference framework depicting the thermodynamic
hierarchy of the phases available to the system under the
relevant processing conditions. When transformations are
partitionless the phase menu and hierarchy can be readily derived
from the relative position of the T0 curves/surfaces for the
different pairs of phases. The result is a phase hierarchy map,
which is an analog of the phase diagram for partitionless
equilibrium. Such maps can then be used to assess the kinetic
effects on the selection of metastable states and their
subsequent evolution.
This presentation will discuss the evolution of metastable phases
in oxides, with emphasis on systems involving fluorite phases and
their ordered or distorted derivatives. The concepts will be
illustrated primarily with zirconia-based systems, notably those
of interest in thermal barrier coatings, fuel cells and
ferroelectrics (ZrO$_2$-MO$_{3/2}$, where M = Y, Sc, the
lanthanides and combinations thereof, as well as
ZrO$_2$-YO$_{3/2}$-TiO$_2$, ZrO$_2$-TiO$_2$-PbO, etc.). Of
particular interest are the durabilities of metastable phases in
systems that operate at high temperature, their decomposition
paths and the implications to their functionality.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.W5.2