Self Diffusion in Solid 4He and 3He-4He Mixtures Near the bcc-hcp Phase Transition
Self Diffusion in Solid 4He and 3He-4He Mixtures Near the bcc-hcp Phase Transition
复制标题
固体 4He 和 3He-4He 混合物中 bcc-hcp 相变附近的自扩散
DOI：
10.1023/a:1022384618191
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发表时间：
1998
影响因子：
2
通讯作者：
E. Polturak
中科院分区：
文献类型：
--
作者：
Inon Berent;E. Polturak
我们报道了固体4he和3he - 4he混合物的1.4%和2.8%在bcc-hcp过渡附近的塑性流动实验。塑性流动是通过使导线穿过宏观单晶而产生的。我们发现纯氦和混合氦晶体的塑性流动速率在bcc-hcp相变附近都有提高。结果用固体中的自扩散来解释。纯he和混合物的自扩散系数d值与各自的转变温度非常接近，并达到正常液体的自扩散系数d值。混合物中的自扩散活化能比纯4he低3 K。我们认为，与在金属中观察到的情况类似，固体He中的自扩散是通过声子辅助的原子空位交换发生的。在bcc- hcp跃迁附近的扩散增强是短波长的横向声子软化的结果。利用我们的数据计算的声子能量的温度依赖性符合朗道的软模驱动相变理论。在混合晶体中观察到加工硬化，而在纯4he中没有。这意味着3he杂质会导致位错线。
We report experiments on the plastic flow of solid4He and3He-4He mixtures of 1.4% and 2.8% near thebcc-hcptransition. Plastic flow was generated by moving a wire through a macroscopic single crystal. We found that the plastic flow rate both in pure4He and in mixture helium crystals is enhanced in vicinity of thebcc-hcpphase transition. The results are interpreted in terms of self diffusion in the solid. Values of the self diffusion coefficient Dsat the respective transition temperatures of pure4He and of the mixtures are very close, and reach that found in normal liquids. The activation energy for self diffusion in the mixtures is lower by up to 3 K than in pure4He. We suggest that similar to what is observed inbccmetals, self-diffusion in solid He takes place through phonon assisted atom-vacancy exchange. The enhancement of the diffusion near thebcc-hcptransition is a result of the softening of a short wavelength transverse phonon. The temperature dependence of the energy of the phonon calculated using our data is in accord with the Landau theory of a phase transition driven by a soft mode. Work hardening was observed in mixture crystals, but not in pure4He. This implies that3He impurities pin dislocation lines.