Phase transition of Zr1-xHfxV2O7 solid solutions having negative thermal expansion
Phase transition of Zr1-xHfxV2O7 solid solutions having negative thermal expansion
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DOI：
10.2109/jcersj.114.607
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发表时间：
2006-07-01
影响因子：
1.1
通讯作者：
Yamamura, Yasuhisa
中科院分区：
文献类型：
--
作者：
Hisashige, Tetsuo;Yamaguchi, Teppei;Yamamura, Yasuhisa
用X射线衍射、TMA和DSC等方法研究了Zr（IV）取代后的Zr 1-xHfxV 2 O 7（x=0-1）固溶体的相变。X射线衍射实验表明，所有组成的Zr_（1-x）Hf_xV_2 O_7（x=0-1）都是具有立方结构的单相。由于Hf（IV）离子的离子半径小于Zr（IV）离子的离子半径，Zr（1-xHfxV 2 O 7）（x=0-1）的室温晶格常数随Hf含量的增加而线性减小。在T-1=350 K和T-2=375 K附近的两个相变温度下，所有样品在TMA中均观察到突然的正热膨胀，在380 K以上观察到负热膨胀。DSC测量清楚地表明，所有的Zr 1-xHfxV 2 O 7（x=0-1）样品也经历了两个连续的相变之间的330和390 K。Zr 1-xHfxV 2 O 7（x=0-1）样品的两个转变温度和相变温度随x含量的增加而降低，反映了超晶格结构的降低。连续两个相变的跃迁熵之和随室温下超晶格线归一化相对强度的增加而增加。
The phase transition of Zr1-xHfxV2O7 (x=0-1) Solid solutions substituted for Zr(IV) sites was investigated using X-ray diffraction, TMA and DSC methods. X-ray diffraction experiments revealed that all compositions of Zr1-xHfxV2O7 (x=0-1) were of a single phase having a cubic structure. Lattice parameters of Zr1-xHfxV2O7 (x=0-1) at room temperature decreased linearly with increasing Hf content, due to the smaller ionic radius of the Hf (IV) ion than that of the Zr (IV) ion. Abrupt positive thermal expansions in TMA were observed for all samples at two phase transition temperatures in the vicinity of T-1=350 K and T-2=375 K, and negative thermal expansions were seen above about 380 K. DSC measurements clearly showed that all of the Zr1-xHfxV2O7 (x=0-1) samples also underwent two successive phase transitions between 330 and 390 K. Two transition temperatures and phase transition enthalpies of Zr1-xHfxV2O7 (x=0-1) samples decreased with the increase of x content, reflecting the decrease of superlattice structure. The sum of transition entropy for successive two phase transitions increased with increasing the normalized relative intensity of the superlattice line at room temperature.