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Title: Negative thermal expansion in ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8}

Abstract

Isostructural ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8} show strong negative thermal expansion from 0.3 K up to their decomposition temperatures of approximately 1050 K. This behavior is especially unusual because these compounds are apparently cubic over their entire existence range. Detailed structural studies of ZrW{sub 2}O{sub 8} were conducted using high-resolution neutron powder diffraction data taken at 14 temperatures from 0.3 to 693 K. Below 428 K, ZrW{sub 2}O{sub 8} adopts the acentric space group P2{sub 1}3 and has a well-ordered structure containing corner-sharing ZrO{sub 6} octahedra and two crystallographically distinct WO{sub 4} tetrahedra. Above the phase transition at 428 K, which appears to be second order, the space group becomes centric Pa3. The structure is now disordered with one oxygen site 50% occupied, suggesting the possibility of high oxygen mobility. Oxygen motion above 428 K is also suggested by dielectric and ac impedance measurements. The negative thermal expansion of ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8} is related to transverse thermal vibrations of bridging oxygen atoms. These lead to coupled rotations of the essentially rigid polyhedral building blocks of the structure. A semiquantitative model for both the negative thermal expansion and phase transition of these materials is proposedmore » in light of the diffraction results. 71 refs., 15 figs., 3 tabs.« less

Authors:
; ;  [1]
  1. Oregon State Univ., Corvallis, OR (United States); and others
Publication Date:
OSTI Identifier:
518368
Resource Type:
Journal Article
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 8; Journal Issue: 12; Other Information: PBD: Dec 1996
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ZIRCONIUM OXIDES; THERMAL EXPANSION; TUNGSTEN OXIDES; HAFNIUM OXIDES; PHASE TRANSFORMATIONS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0000-0013 K; TEMPERATURE RANGE 0013-0065 K; TEMPERATURE RANGE 0065-0273 K; TEMPERATURE RANGE 0400-1000 K; CUBIC LATTICES; NEUTRON DIFFRACTION

Citation Formats

Evans, J S.O., Mary, T A, and Sleight, A W. Negative thermal expansion in ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8}. United States: N. p., 1996. Web. doi:10.1021/cm9602959.
Evans, J S.O., Mary, T A, & Sleight, A W. Negative thermal expansion in ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8}. United States. doi:10.1021/cm9602959.
Evans, J S.O., Mary, T A, and Sleight, A W. Sun . "Negative thermal expansion in ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8}". United States. doi:10.1021/cm9602959.
@article{osti_518368,
title = {Negative thermal expansion in ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8}},
author = {Evans, J S.O. and Mary, T A and Sleight, A W},
abstractNote = {Isostructural ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8} show strong negative thermal expansion from 0.3 K up to their decomposition temperatures of approximately 1050 K. This behavior is especially unusual because these compounds are apparently cubic over their entire existence range. Detailed structural studies of ZrW{sub 2}O{sub 8} were conducted using high-resolution neutron powder diffraction data taken at 14 temperatures from 0.3 to 693 K. Below 428 K, ZrW{sub 2}O{sub 8} adopts the acentric space group P2{sub 1}3 and has a well-ordered structure containing corner-sharing ZrO{sub 6} octahedra and two crystallographically distinct WO{sub 4} tetrahedra. Above the phase transition at 428 K, which appears to be second order, the space group becomes centric Pa3. The structure is now disordered with one oxygen site 50% occupied, suggesting the possibility of high oxygen mobility. Oxygen motion above 428 K is also suggested by dielectric and ac impedance measurements. The negative thermal expansion of ZrW{sub 2}O{sub 8} and HfW{sub 2}O{sub 8} is related to transverse thermal vibrations of bridging oxygen atoms. These lead to coupled rotations of the essentially rigid polyhedral building blocks of the structure. A semiquantitative model for both the negative thermal expansion and phase transition of these materials is proposed in light of the diffraction results. 71 refs., 15 figs., 3 tabs.},
doi = {10.1021/cm9602959},
journal = {Chemistry of Materials},
number = 12,
volume = 8,
place = {United States},
year = {1996},
month = {12}
}