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Phase Transition and Negative Thermal Expansion in Tetragonal NbOPO4

✍ Scribed by T.G. Amos; A. Yokochi; A.W. Sleight

Publisher: Elsevier Science
Year: 1998
Tongue: English
Weight: 304 KB
Volume: 141
Category: Article
ISSN: 0022-4596
DOI: 10.1006/jssc.1998.8045

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✦ Synopsis

The structure of tetragonal NbOPO 4 has been studied from room temperature to 500°°C by X-ray powder diffraction and to 327°°C by neutron powder diffraction. Rietveld refinements were conducted on neutron data collected at 25, 100, 175, 200, 225, 275, and 327°°C. A phase transition was found at about 200°°C. The space group is P4/n below this transition and P4/nmm above this transition. The c cell edge shows positive thermal expansion over the entire temperature range. The a and b cell edges show positive thermal expansion below the transition and negative thermal expansion above the transition. The negative thermal expansion is attributed to rocking motions of the corner-shared NbO 6 octahedra and PO 4 tetrahedra.

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