Study of Negative Thermal Expansion and Shift in Phase Transition Temperature in Ti4+- and Sn4+-Substituted ZrW2O8 Materials

The negative-thermal-expansion material ZrW2O8 is known to undergo an order−disorder phase transition which affects its expansion behavior. In this study, Ti4+ and Sn4+ are examined as possible substituting ions for the Zr4+ position in ZrW2O8. This substitution leads to a decrease in cell parameters, as the ionic radii of the substituents are smaller than the Zr4+ ionic radius. A remarkable decrease in transition temperature is noticed. DSC is used to quantify the enthalpy and entropy changes during the phase transition in order to reveal the mechanisms behind this decrease. It is shown that the strength of the M−O bond plays an important role, as it is a partner in the rigid unit mode motion and the order−disorder transition mechanism.