Thermal equations of state for B1 and B2 KCl
Thermal equations of state for B1 and B2 KCl
复制标题
B1 和 B2 KCl 的热状态方程
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
S. Buhre
中科院分区：
文献类型：
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作者：
D. Walker;L. Cranswick;P. Verma;S. Clark;S. Buhre
固体的压缩性通常随着压缩的进行而下降。在同一结构中，随着密度的增加，键变短变硬。然而，在许多测量的碱卤化物中，对于B1-B2相的转变，键长随着向致密相的转变而增加。红外模式频率降低（Hofmeister 1997），导致反直觉的期望，即压缩性应该在进入密度更大的B2阶段时增加。过去的体积测量在识别任何这种压缩性增加方面充其量是模棱两可的。CLRC Daresbury实验室16.4站原位x射线衍射测量相体积得到的B1和B2 KCl的新状态热方程，对于可压缩性在转变过程中是增加还是减少的问题同样模棱两可。相比之下，新的体积测量表明，从B1到B2 KCl的热膨胀增加很容易解决。产物a·K比α和K更为人所知，从B1的0.0195±0.0005 kbar/°C增加到B2 KCl的0.0275±0.0009 kbar/°C。Yagi（1978）证明了KF的类似增加，这主要是由a的增加所支持的。RbCl也出现了这种增加（Walker et al. 2001）。热膨胀增加所表明的键变弱与预期在B1-B2转变过程中难以捉摸的可压缩性增加是一致的，但这并不能从体积测量中得到解决。在整个转变过程中，热效应比压缩效应对α·K的影响更为明显。减压后键紧降低了α，增加了固体粘度，从而降低了瑞利数。随着配位数的减小而发生减压相变的材料上升流，其对流轻快度可以在这种相变中得到抑制
Abstract Compressibility of solids generally drops as compression proceeds. Bonds shorten and stiffen with density increase in the same structure. However for the B1-B2 phase transition in many measured alkali halides, bond lengths increase in going to the denser phase. And IR mode frequencies decrease (Hofmeister 1997), leading to the counter-intuitive expectation that compressibility should increase in going to the denser B2 phase. Past volume measurements have been equivocal at best in recognizing any such compressibility increase. New thermal equations of state for B1 and B2 KCl from in-situ X-ray diffraction measurements of phase volumes on Station 16.4 of the CLRC Daresbury Laboratory are no less equivocal about the issue of whether compressibility increases or decreases across the transition. In contrast, the new volume measurements show an easily resolved thermal expansion increase in going from B1 to B2 KCl. The product a·K, which is better known than either α or K, increases from 0.0195 ± 0.0005 kbar/°C in B1 to 0.0275 ± 0.0009 kbar/°C in B2 KCl. Yagi (1978) demonstrated a similar increase for KF, also supported mainly by increases in a. This increase can also be seen in RbCl (Walker et al. 2001). Bond weakening indicated by the thermal expansion increase is consistent with the elusive compressibility increase that is expected across the B1-B2 transition but which is not resolved from volume measurements. The thermal effects are more visible than the compressional effects on α·K across the transition. Bond tightening upon decompression reduces α, increases solid viscosity, and hence decreases the Rayleigh number. An upwelling of material undergoing a decompression phase change with decrease of coordination number may have its convective friskiness damped at such a transition