High Solubility of Hetero-Valence Ion (Cu2+) for Reducing Phase Transition and Thermal Expansion of ZrV1.6P0.4O7.

Large thermal expansion at room temperature and high phase transition temperature of ZrV₂O₇ limit its practical applications and are reduced by the high solubility of hetero-valence ion (Cu²⁺) on the basis of an equal-valence substitution of P⁵⁺ for V⁵⁺. The temperature-dependent Raman spectra show that Zr_0.9 Cu_0.1 V_1.6 P_0.4 O_6.9 maintains a normal parent cubic structure till 173K and transforms to a 3 × 3 × 3 cubic superstructure below 173K. Temperature dependent x-ray diffraction patterns of Zr_0.9 Cu_0.1 V_1.6 P_0.4 O_6.9 show near zero and negative thermal expansion. High solubility of lower valence Cu²⁺ relates to an equal-valence substitution of smaller P⁵⁺ for V⁵⁺, which extends the bond angle of V(P)—O—V in ZrV_1.6 P_0.4 O₇ close to 180°. The change of microstructure is considered to be responsible for reduced phase transition temperature and thermal expansion. [ABSTRACT FROM AUTHOR]