Phase Transition and Negative Thermal Expansion in Tetragonal NbOPO₄

In this: publication
By this: publisher
In this Subject: <a title="Chemistry (General)" href="/content/subcat?j_subject=166&j_availability=">Chemistry (General)
By this author: Amos T.G. ;&nbsp; Yokochi A. ;&nbsp; Honig A.J.W.M.

Authors: Amos T.G.; Yokochi A.; Honig A.J.W.M.

Source: Journal of Solid State Chemistry, Volume 141, Number 1, November 1998 , pp. 303-307(5)

Buy & download fulltext article:

Price: $52.63 plus tax (Refund Policy)

Abstract:

The structure of tetragonal NbOPO₄ 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 NbO₆ octahedra and PO₄ tetrahedra. Copyright 1998 Academic Press.