High-pressure melting behavior of tin up to 105 GPa
High-pressure melting behavior of tin up to 105 GPa
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DOI：
10.1103/physrevb.95.054102
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发表时间：
2017-02-03
影响因子：
3.7
通讯作者：
McMillan, P. F.
中科院分区：
文献类型：
--
作者：
Briggs, R.;Daisenberger, D.;McMillan, P. F.
Sn的熔化曲线随压力的变化曲线开始急剧上升，但在40 GPa以上斜率（dT(m)/dP）逐渐减小，在50 GPa以上趋于平缓。以前的研究认为，在室温下，在这个范围内发生了体心四边形（bct）到立方（bcc）的相变。然而，我们的研究表明，该区域的相行为更为复杂，在32 GPa以上的x射线衍射模式中出现了正交分裂（bco）反射，并且在40和70 GPa之间观察到bco和bcc结构共存的衍射特征。在这里，我们已经记录了bco和bcc反射同时存在直到熔点，否定了它们共存可能表明动力学阻碍一阶相变的可能性。本文利用x射线衍射图中的液体漫射散射现象和热信号处理过程中的不连续现象，将锡熔化关系的观测扩展到兆巴（P > 100 GPa）范围，以诊断熔化的发生。这两种技术都能得出一致的结果，表明在检测的最高压力下，熔化线保持相同的低斜率，不会变平。在约40 GPa以下的结果与最近使用拟合现有或假设数据的多相状态方程得出的熔化关系吻合得很好。在此压力以上，实验熔点越来越低于预测的晶体-液相边界，但高于过去研究的平坦熔点，表明体心“γ”-Sn结构的热力学性质仍有待澄清。
The melting curve of Sn initially rises steeply as a function of pressure but exhibits a decrease in slope (dT(m)/dP) above 40 GPa to become nearly flat above 50 GPa. Previous studies have argued that a body-centered tetragonal (bct) to cubic (bcc) phase transition occurs in this range at room temperature. However, our investigations have shown that the phase behavior is more complex in this region with orthorhombic (bco) splitting of reflections occurring in the x-ray diffraction pattern above 32 GPa and coexisting diffraction signatures of bco and bcc structures are observed between 40 and 70 GPa. Here we have documented the simultaneous presence of bco and bcc reflections up to the melting point, negating the possibility that their coexistence might indicate a kinetically hindered first-order phase transformation. In this paper we have extended the observation of Sn melting relations into the megabar (P > 100 GPa) range using the appearance of liquid diffuse scattering in x-ray diffraction patterns and discontinuities during thermal signal processing to diagnose the occurrence of melting. Both techniques yield consistent results that indicate the melting line maintains the same low slope up to the highest pressure examined and does not flatten. The results below approximately 40 GPa agree well with the melting relations produced recently using a multiphase equation of state fitted to available or assumed data. Above this pressure the experimental melting points lie increasingly below the predicted crystal-liquid phase boundary, but above the flat melting from past studies, indicating that the thermodynamic properties of the body-centered "gamma" -Sn structure remain to be clarified.