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Low-temperature heat capacities and Raman spectra of negative thermal expansion compounds ZrW 2 O 8 and HfW 2 O 8

Low-temperature heat capacities and Raman spectra of negative thermal expansion compounds ZrW 2 O... Heat capacities of ZrW 2 O 8 and HfW 2 O 8 were precisely measured between 1.8 and 330 K. Heat-capacity curves of ZrW 2 O 8 and HfW 2 O 8 are very similar to each other. The heat capacity of HfW 2 O 8 at low temperature is larger than that of ZrW 2 O 8 due to atomic mass effect, but both heat capacities cross around 220 K. Raman spectra of ZrW 2 O 8 and HfW 2 O 8 were recorded at room temperature. Frequency distributions of lattice vibrations were estimated through an analysis of the heat capacities for ZrW 2 O 8 and HfW 2 O 8 . It is found that the difference in the frequency distributions between ZrW 2 O 8 and HfW 2 O 8 arises from the different atomic mass and bond strength, and causes the different temperature dependence of the heat capacities. The properties of the optical-phonon modes with a large negative mode-Grüneisen parameter are discussed. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review B American Physical Society (APS)

Low-temperature heat capacities and Raman spectra of negative thermal expansion compounds ZrW 2 O 8 and HfW 2 O 8

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Publisher
American Physical Society (APS)
Copyright
Copyright © 2002 The American Physical Society
ISSN
1095-3795
DOI
10.1103/PhysRevB.66.014301
Publisher site
See Article on Publisher Site

Abstract

Heat capacities of ZrW 2 O 8 and HfW 2 O 8 were precisely measured between 1.8 and 330 K. Heat-capacity curves of ZrW 2 O 8 and HfW 2 O 8 are very similar to each other. The heat capacity of HfW 2 O 8 at low temperature is larger than that of ZrW 2 O 8 due to atomic mass effect, but both heat capacities cross around 220 K. Raman spectra of ZrW 2 O 8 and HfW 2 O 8 were recorded at room temperature. Frequency distributions of lattice vibrations were estimated through an analysis of the heat capacities for ZrW 2 O 8 and HfW 2 O 8 . It is found that the difference in the frequency distributions between ZrW 2 O 8 and HfW 2 O 8 arises from the different atomic mass and bond strength, and causes the different temperature dependence of the heat capacities. The properties of the optical-phonon modes with a large negative mode-Grüneisen parameter are discussed.

Journal

Physical Review BAmerican Physical Society (APS)

Published: Jul 1, 2002

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