Thermal Analysis of Phase Transition in Negative-Thermal-Expansion Oxide, ZrW2O8
Thermal Analysis of Phase Transition in Negative-Thermal-Expansion Oxide, ZrW2O8
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负热膨胀氧化物 ZrW2O8 相变的热分析
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
Y. Morito
中科院分区：
文献类型：
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作者：
T. Hashimoto;Y. Morito
在干燥的氮气气氛下，获得了负热膨胀氧化物ZrW2O8的差示扫描量热法(DSC)曲线。在加热测量时，在124℃和169℃分别观察到一个吸热峰和基线漂移。在连续的冷却和加热测量中，重现了169°C的基线移动，但在124°C的峰值在两条曲线上都消失了。169℃时的基线漂移对应于热膨胀系数的变化，这是由于结构相变引起的，即从具有P213空间群的偏心立方相(第198号空间群)到具有PA3空间群的中心相(第205号空间群)。热重(TG)和热重-差热分析-质谱仪(TG-DTA-MS)的同时测量表明，在124℃处的吸热峰的来源是与ZrW2O8样品有关的H2O的分离，其量小于1.6mol%。结果表明，微量H2O对材料的热膨胀行为影响不大，热膨胀系数在164C附近的变化可归因于λ相变。
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.