熱収縮性酸化物ZrW_2O_8の構造相転移の熱分析 : 微少量H_2O及びλ転移の検出

概要

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Differential scanning calorimetry (DSC) curves of negative-thermal-expansion oxide, ZrW_2O_8, were obtained under dry N_2 atmosphere. An endothermic peak and base-line shift were observed at 124 and 169℃, respectively, upon heating measurements of as-prepared ZrW_2O_8. Upon successive cooling and heating measurements, the base-line shift at 169℃ was reproduced, however, the peak at 124℃ disappeared in both curves. The base-line shift at 169℃ 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 P2_13 (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℃ was the secession of H_2O involved with the ZrW_2O_8 specimen, whose amount was less than 1.6 mol%. It was clarified that the trace amount of H_2O negligibly affected the thermal expansion behavior of ZrW_2O_8 and that the variation of the thermal expansion coefficient around 164℃ could be attributed to the A-type transition.
2002-09-01