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Title: Pressure Induced Phase Transformations in Ceramics

Abstract

The study of materials with unusual properties offers new insight into structure-property relations as well as promise for the design of novel composites. In this spirit, the PIs seek to (1) understand fundamental mechanical phenomena in ceramics that exhibit pressure-induced phase transitions, negative coefficient of thermal expansion (CTE), and negative compressibility, and (2) explore the effect of these phenomena on the mechanical behavior of composites designed with such ceramics. The broad and long-term goal is to learn how to utilize these unusual behaviors to obtain desired mechanical responses. While the results are expected to be widely applicable to many ceramics, most of the present focus is on silicates, as they exhibit remarkable diversity in structure and properties. Eucryptite, a lithium aluminum silicate (LiAlSiO 4), is specifically targeted because it exhibits a pressure-induced phase transition at a sufficiently low pressure to be accessible during conventional materials processing. Thus, composites with eucryptite may be designed to exhibit a novel type of transformation toughening. The PIs have performed a combination of activities that encompass synthesis and processing to control structures, atomistic modeling to predict and understand structures, and characterization to study mechanical behavior. Several materials behavior discoveries were made. It was discovered thatmore » small amounts of Zn (as small as 0.1 percent by mol) reverse the sign of the coefficient of thermal expansion of beta-eucryptite from negative to slightly positive. The presence of Zn also significantly mitigates microcracking that occurs during thermal cycling of eucryptite. It is hypothesized that Zn disrupts the Li ordering in beta-eucryptite, thereby altering the thermal expansion behavior. A nanoindentation technique developed to characterize incipient plasticity was applied to examine the initial stages of the pressure induced phase transformation from beta to epsilon-eucryptite and show that the transformation nucleation is related to the motion of the tetrahedral units making up the structure. It was revealed that the conduction of Li ions through the structure is also dictated by the tetrahedral unit arrangement and how their positions change with temperature. The critical pressure to obtain the high pressure phase of eucryptite was shown to depend on the grain size. The structure of the high pressure phase was determined with a combination of atomistic modeling and in situ x-ray diffraction experiments.« less

Authors:
ORCiD logo [1];  [1]
  1. Colorado School of Mines, Golden, CO (United States)
Publication Date:
Research Org.:
Colorado School of Mines, Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
OSTI Identifier:
1412074
Report Number(s):
DOE-CSM-07ER46397
DOE Contract Number:  
FG02-07ER46397
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; phase transformation; ceramics; thermal expansion; conduction; silicates

Citation Formats

Reimanis, Ivar, and Cioabanu, Cristian. Pressure Induced Phase Transformations in Ceramics. United States: N. p., 2017. Web. doi:10.2172/1412074.
Reimanis, Ivar, & Cioabanu, Cristian. Pressure Induced Phase Transformations in Ceramics. United States. doi:10.2172/1412074.
Reimanis, Ivar, and Cioabanu, Cristian. Sun . "Pressure Induced Phase Transformations in Ceramics". United States. doi:10.2172/1412074. https://www.osti.gov/servlets/purl/1412074.
@article{osti_1412074,
title = {Pressure Induced Phase Transformations in Ceramics},
author = {Reimanis, Ivar and Cioabanu, Cristian},
abstractNote = {The study of materials with unusual properties offers new insight into structure-property relations as well as promise for the design of novel composites. In this spirit, the PIs seek to (1) understand fundamental mechanical phenomena in ceramics that exhibit pressure-induced phase transitions, negative coefficient of thermal expansion (CTE), and negative compressibility, and (2) explore the effect of these phenomena on the mechanical behavior of composites designed with such ceramics. The broad and long-term goal is to learn how to utilize these unusual behaviors to obtain desired mechanical responses. While the results are expected to be widely applicable to many ceramics, most of the present focus is on silicates, as they exhibit remarkable diversity in structure and properties. Eucryptite, a lithium aluminum silicate (LiAlSiO4), is specifically targeted because it exhibits a pressure-induced phase transition at a sufficiently low pressure to be accessible during conventional materials processing. Thus, composites with eucryptite may be designed to exhibit a novel type of transformation toughening. The PIs have performed a combination of activities that encompass synthesis and processing to control structures, atomistic modeling to predict and understand structures, and characterization to study mechanical behavior. Several materials behavior discoveries were made. It was discovered that small amounts of Zn (as small as 0.1 percent by mol) reverse the sign of the coefficient of thermal expansion of beta-eucryptite from negative to slightly positive. The presence of Zn also significantly mitigates microcracking that occurs during thermal cycling of eucryptite. It is hypothesized that Zn disrupts the Li ordering in beta-eucryptite, thereby altering the thermal expansion behavior. A nanoindentation technique developed to characterize incipient plasticity was applied to examine the initial stages of the pressure induced phase transformation from beta to epsilon-eucryptite and show that the transformation nucleation is related to the motion of the tetrahedral units making up the structure. It was revealed that the conduction of Li ions through the structure is also dictated by the tetrahedral unit arrangement and how their positions change with temperature. The critical pressure to obtain the high pressure phase of eucryptite was shown to depend on the grain size. The structure of the high pressure phase was determined with a combination of atomistic modeling and in situ x-ray diffraction experiments.},
doi = {10.2172/1412074},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2017},
month = {10}
}