Study of Ti4+ substitution in ZrW2O8 negative thermal expansion materials

摘要

Powder XRD-analysis and thermo-mechanical analysis on sintered TiO2-WO3-ZrO2 mixtures revealed the formation of Zr1-xTixW2O8 solid solutions. A noticeable decrease in unit cell parameter 'a' and in the order-disorder transition temperature could be seen in the case of Zr1-xTixW2O8 solid solutions. Studies performed on other ZrW2O8 solid solutions have attributed an increase in phase transition temperature to a decrease in free lattice volume, whereas a decrease in phase transition temperature was suggested to be due to the presence of a more disordered state. Our studies indicate that the phase transition temperature in our materials is strongly influenced by the bond dissociation energy of the substituting ion-oxygen bond. A decrease in bond strength may compensate for the effect of a decrease in lattice free volume, lowering the phase transition temperature as the degree of substitution by Ti4+ increases. This hypothesis is proved by differential scanning calorimetry. (C) 2007 Elsevier Inc. All rights reserved.