Effects of Nb and Y substitution on negative thermal expansion of ZrV2-xPxO7 (0 ≤ X ≤ 0.8)

Zirconium vanadates with a novel chemical composition including niobium and yttrium were synthesized by the sol-gel method. An aqueous solution of NH4H2PO4 and NH4VO3 and an ethanol solution of ZrOCl2, NbCl5, and YCl3 were prepared. These two solutions were stirred and mixed to prepare precursors of zirconium vanadates at 333 K, following the evaporation of the solvent at 363 K. The precursor gels obtained were heated at 373-973 K in air. A zirconium vanadate phase began to crystallize above 673 K and a single phase of zirconium vanadate was synthesized at 973 K. Although ZrV2O7 generally had a positive thermal expansion in the temperature range above RT, the degree of positive thermal expansion decreased with the two types of substitution of P for V and a set of Nb and Y for Zr of ZrV2O7. X-ray diffraction peaks due to a superlattice structure, causing a positive thermal expansion from RT, were not observed in the synthesized (Nb, Y)-substituted zirconium vanadates. (C) 2011 Elsevier Ltd. All rights reserved.