Reducing ultra-low thermal expansion of β-Zr2O(PO4)2 by substitutions?

The ultra-low thermal expansion of β-Zr2O(PO4)2 could still be reduced by chemical modifications, according to previous works on uranium and thorium IV homologues that evidenced a contracting effect of big cations. However, the present study shows that the only isovalent cations likely to substitute for ZrIV or PV are either harmful, or unstable, chemically or thermally. Furthermore, aliovalent modifications seem to be forbidden by the crystal structure of the material, leaving probably very few perspectives of improvement. Vanadium however improves significantly the crystallinity of the material and lowers the α–β transition temperature.