Beta-Zirconium Oxide Monophosphate: Structural Keys for an Ultralow Expansion Material

Rietveld analyses performed on high-temperature X-ray (HTXRD) and neutron (HTND)
powder patterns of β-(Zr2O)(PO4)2 have allowed us to follow accurately the thermal variations
of the cell parameters and to explain its strong dilatometric anisotropy in terms of structural
distortions. It appeared that the anomaly resulted from two simultaneous mechanical
effects:  libration movements of the bridging oxygen atoms related to a rocking of the ZrO7
and PO4 polyhedra and a rotation effect resulting from electrostatic repulsions between ZrIV
cations of neighbor polyhedra. Both effects lead to a strong shrinkage of the b parameter
and contribute to the ultralow overall expansion that has made β-(Zr2O)(PO4)2 famous as a
thermal-shock resistant material.