Why does uranium oxide phosphate contract on heating?

G. Wallez (1) , S. Launay (1) , M. Quarton (1) , N. Dacheux (2) , J.-L. Soubeyroux (3)

1 LCS - Laboratoire de Cristallochimie du Solide
2 IPNO - Institut de Physique Nucléaire d'Orsay
3 ILL - Institut Laue-Langevin

(U2O)(PO4)2 is related to ultra-low expansion β-(Zr2O)(PO4)2 ceramics, but shows a continuous thermal contraction. High-temperature neutron diffraction has allowed to follow accurately the thermal variations of its cell edges and to give a structural explanation to the phenomenon: like in β-(Zr2O)(PO4)2, the dilatometric anomaly arises simultaneously from a contractive push–pull effect due to Coulombic repulsions and from a libration of the PO4 and UO7 polyhedra, but in the present case, the second mechanism predominates. The size of the tetravalent cation appears as a key parameter in monitoring the thermal expansion of ceramics of this family.

Mots clés: Negative thermal expansion; Neutron diffraction; Crystalline oxides; Ceramics

Domaines: Chimie-Physique [physics.chem-ph]

G. Wallez, S. Launay, M. Quarton, N. Dacheux, J.-L. Soubeyroux. Why does uranium oxide phosphate contract on heating?. Journal of Solid State Chemistry, 2004, 177, pp.3575-3580. ⟨10.1016/j.jssc.2004.06.014⟩. ⟨in2p3-00025662⟩