zirconium tungstate ZrW2O8

Negative Thermal Expansion of ZrW₂O₈

ZrW2O8 has been show to exhibit negative thermal expansion over a wide temperature range.
This property has been related to the unusual topology of the structure, which exhibits a large number of rigid unit modes. These can be described as vibrations in which the constituent ZrO6 octahedra and WO4 tetrahedra of ZrW2O8 are undistorted. Many of these modes have a negative Gruneisen parameter and thus tend to cause a contraction of the structure when populated. These are low energy modes and thus remain populated even at very low temperatures. Physical measurements by Ramirez and co-workers support this basic model. Much of our work on ZrW2O8 has been performed in collaboration with Art Sleight of Oregon State University.

The cubic structure of ZrW2O8
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Watch animations showing the potential structural flexibility of ZrW2O8:

At 448 K cubic a-ZrW2O8 undergoes a phase transition to b-ZrW2O8 which contains disordered oxygen ions. This phase transition involves oxygen migration, and can be thought of as reversing the direction in which pairs of WO4 tetrahedra are oriented in the structure.

Schematic of oxygen migration in ZrW2O8

Under applied pressure cubic a-ZrW2O8 undergoes a phase transition to orthorhombic g-ZrW2O8. This phase transition involves first a migration of oxygen, then a coupled rotation of polyhdedral units. The final structure contains cross linked WOn polyhedra in which all the oxygen atoms are 2-coordinate.

Schematic of high pressure phase transition

More detailed information on our work on ZrW2O8 is available in the following references:

J. S. O. Evans, W. I. F. David and A. W. Sleight, "Structural Investigation of the Negative Thermal Expansion Material ZrW2O8", Acta Cryst. B, 1999, 55, 333-40.

W. I. F. David, J. S. O. Evans and A. W. Sleight, "Direct Evidence for a Low Frequency Phonon Mode Mechanism in the Negative Thermal Expansion Compound ZrW2O8", Europhys. Lett., 1999, 46, 666-669.

J. S. O. Evans, T. A. Mary, T. Vogt, M. A. Subramanian and A. W. Sleight, "Negative Thermal Expansion in ZrW2O8 and HfW2O8", Chem. Mater., 1996, 8, 2809-2823.

T. A. Mary, J. S. O. Evans, T. Vogt and A. W. Sleight, "Negative thermal expansion from 0.3 to 1050 Kelvin in ZrW2O8", Science, 1996, 272, 90-92.

J. S. O. Evans, J. Jorgensen, R. M. Ibberson, W. I. F. David and A. W. Sleight, "Thermal Expansion in the Orthorhombic g Phase of ZrW2O8", Phys. Rev. B, 1999, submitted.

J. D. Jorgensen, Z. Hu, S. Teslic, D. N. Argyriou, S. Short, J. S. O. Evans and A. W. Sleight, "Pressure-induced cubic-to-orthorhombic phase transition in ZrW2O8", Phys. Rev. B, 1999, 59, 215-225.

J. S. O. Evans, Z. Hu, J. D. Jorgensen, D. N. Argyriou, S. Short and A. W. Sleight, "Compressibility, phase transitions, and oxygen migration in zirconium tungstate, ZrW2O8", Science, 1997, 275, 61-65.

Z. Hu, J. D. Jorgensen, S. Teslic, S. Short, D. N. Argyriou, J. S. O. Evans and A. W. Sleight, "Pressure-induced phase transformation in ZrW2O8 - Compressibility and thermal expansion of the orthorhombic phase", Physica B, 1997, 241, 370-372.

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Modified 30-Jan-2011 by John S.O. Evans.