Abstract
Differential scanning calorimetry (DSC) curves of negative-thermal-expansion oxide, ZrW2O8, were obtained under dry N2 atmosphere. An endothermic peak and base-line shift were observed at 124 and 169°C, respectively, upon heating measurements of as-prepared ZrW2O8. Upon successive cooling and heating measurements, the base-line shift at 169°C was reproduced, however, the peak at 124°C disappeared in both curves. The base-line shift at 169°C corresponded to the variation of the thermal expansion coefficient due to a structural phase transition from the acentric cubic phase with the space group of P213 (No. 198) to the centric phase with the space group of Pa3 (No. 205). Thermogravimetry (TG) and thermogravimetry differential thermal analysis mass spectroscopy (TG-DTA-MS) simultaneous measurement revealed that the origin of the endothermic peak at 124°C was the secession of H2O involved with the ZrW2O8 specimen, whose amount was less than 1.6 mol%. It was clarified that the trace amount of H2O negligibly affected the thermal expansion behavior of ZrW2O8 and that the variation of the thermal expansion coefficient around 164°C could be attributed to the λ-type transition.
