Study of Ti substitution in ZrW2O8 negative thermal expansion materials

Powder XRD-analysis and thermo-mechanical analysis on sintered TiO₂-WO₃-ZrO₂ mixtures revealed the formation of Zr_1−xTi_xW₂O₈ solid solutions. A noticeable decrease in unit cell parameter ‘a’ and in the order-disorder transition temperature could be seen in the case of Zr_1−xTi_xW₂O₈ 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.