The thermodynamic effect of nonhydrostatic stress on the Verwey transition
The thermodynamic effect of nonhydrostatic stress on the Verwey transition
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DOI：
10.1016/j.epsl.2011.11.021
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发表时间：
2012-02-15
影响因子：
5.3
通讯作者：
Wright, Jonathon P.
中科院分区：
文献类型：
--
作者：
Coe, Robert S.;Egli, Ramon;Wright, Jonathon P.
磁铁矿在压缩下的Verwey转变温度变化的实验结果表现出令人费解的变异性，斜率从-6到+16K/Gpa不等。我们对磁铁矿中Verwey转变的热力学分析很大程度上解释了磁铁矿晶体结构从立方向单斜晶型转变时的转变应变。由于这种应变在形状上的变化比在体积上大得多，所以相界温度(T-v)的变化对非静水压力比对静水压力敏感得多。据预测，单轴压缩和拉伸都会增加T-v，这种影响在符号上是相反的，对于有利的方向，每千兆卡的T-v比压力大6倍。此外，由于具有最高T-v的单斜孪晶取向在热力学上是有利的，我们的处理还展示了如何通过施加适当取向的应力来唯一地选择任何所需的孪晶，从而消除了理解由于存在多个孪晶而导致的磁铁矿中的各种低温现象的障碍。对强磁场的热力学效应也进行了类似的分析，预测T-v将普遍降低。同样，T-v最高(即降低最少)的双胞胎将是最稳定的。每千兆卡应力的孪生选择性是每特斯拉磁场的两到三倍。(C)2011爱思唯尔B.V.保留所有权利。
Experimental results on the change in the Verwey transition temperature in magnetite under compression exhibit puzzling variability, with slopes ranging from -6 to +16 K/GPa. Our thermodynamic analysis of the Verwey transition in magnetite explains much of this variability in terms of the transformation strain as magnetite changes in crystal structure from cubic to monoclinic. Because this strain involves a much larger change in shape than in volume, the change in temperature of the phase boundary (T-v) can be much more sensitive to nonhydrostatic stress than to hydrostatic pressure. Uniaxial compression and tension both are predicted to increase T-v, an effect that is opposite in sign and, for favorable orientations, up to six times greater per gigapascal than for pressure. Moreover, because the monoclinic twin orientation with highest T-v is thermodynamically favored, our treatment also shows how any desired twin may be selected uniquely by applying stress of appropriate orientation, thereby removing obstacles to understanding many kinds of low-temperature phenomena in magnetite caused by the presence of multiple twins. A similar analysis for the thermodynamic effects of strong magnetic fields is outlined, predicting that T-v will generally be lowered. Again, the twin for which T-v is highest (i.e., is lowered the least) will be the most stable. Twin selectivity per gigapascal of stress is up to two to three times stronger than that per Tesla of magnetic field. (C) 2011 Elsevier B.V. All rights reserved.