MATERIALS THAT SHRINK ON HEATING: PRESSURE-INDUCED PHASE TRANSITIONS IN NEGATIVE THERMAL EXPANSION MATERIALS, AND THEIR ENERGETICS
Despite the fact that all chemical bonds expand on heating, a small class of materials shrinks when heated. These, so called negative thermal expansion (NTE) materials, are a unique class of materials with some exotic properties. The present chapter offers insight into the structural aspects of pressure- (or temperature-) induced phase transformations, and the energetics of those changes in these fascinating materials, in particular NTE compound cubic ZrW2O8, orthorhombic Sc2W3O12 and Sc2Mo3O12, as well as other members of the 'scandium tungstate family'. In subsequent sections, (i) combined in situ high-pressure synchrotron XRD and XAS studies of NTE material ZrW2O8; (ii) an in situ high-pressure synchrotron XRD study of Sc2W3O12, Sc2Mo3O12, and Al2W3O12; and (iii) thermochemical studies of the above materials are presented and discussed. In all of these studies, chemical bonds change, sometimes break and new ones form. Correlations between structure, chemistry, and energetics are revealed. It is also shown that (iv) NTE materials are good candidates as precursors to make novel solid state materials, such as the conducting Sc0.67WO4, using high-pressure, high-temperature synthesis, through modification of bonding and electronic structure, and thus provide vast opportunities for scientific exploration.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1033076
- Report Number(s):
- PNNL-SA-77023; TRN: US201202%%578
- Resource Relation:
- Related Information: Advances in Chemistry Research, 10:1-54
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BONDING
CHEMICAL BONDS
CHEMISTRY
ELECTRONIC STRUCTURE
EXPLORATION
HEATING
MODIFICATIONS
PHASE TRANSFORMATIONS
SCANDIUM
SYNCHROTRONS
SYNTHESIS
THERMAL EXPANSION
TUNGSTATES
X-RAY DIFFRACTION
Materials
Shrink
heating
pressure
induced
phase
transitions
negative
thermal
expansion
energetics