Characterization of Dislocations in hcp $$^4\hbox {He}$$ by Torsional Oscillator and Thermal Conductivity Measurements
Characterization of Dislocations in hcp $$^4\hbox {He}$$ by Torsional Oscillator and Thermal Conductivity Measurements
复制标题
通过扭转振荡器和热导率测量表征 hcp $$^4hbox {He}$$ 中的位错
DOI：
10.1007/s10909-022-02669-0
复制
发表时间：
2022
影响因子：
2
通讯作者：
Brazhnikov M
中科院分区：
文献类型：
--
作者：
Brazhnikov M
我们应用两种互补技术来表征 hcp 样品中的移动位错，其浓度是通过封闭毛细管法在摩尔体积 19.5 下生长的，在温度 1.8–2.0 K 退火之前和之后，以及在 0.03 K 下高振幅扭曲和 0.5–1.0 K 下连续恢复加工硬化后。第一种技术依赖于固体氦对振荡扭曲的弹性响应在低于 1 K 的温度下，频率为 161 Hz 和 931 Hz，其中该响应受到移动位错的存在以及不同数量的捕获杂质的影响。监测适度强迫后的非平衡振幅依赖性可以计算移动位错的长度分布n(L)（Iwasa in J Low Temp Phys 171:30, 2013；Fefferman et al. in Phys Rev B 89:014105, 2014）。我们还测试了根据 Fefferman 等人测量的阻尼力值，在小应变幅值下根据剪切模量的实部或虚部的平衡温度依赖性来确定 n(L) 的方法。 。第二种技术利用低于 0.4 K 温度下的热导率测量，即热横向声子的位错限制平均自由程（Greenberg 和 Armstrong，在 Phys Rev B 20:1049, 1979 中；Armstrong 等人在 Phys Rev B 20:1061, 1979 中）。在超过屈服应力的高应变幅值的长时间交流扭转过程中，长位错消失，被许多保持活动的短位错所取代。然而，一旦停止这种扭曲，大多数位错就会变得固定，直到样品加热到 0.5 K 以上，以加速位错恢复到移动状态（Day 等人，在 Phys Rev B 79:214524, 2009 中；Beamish 和 Franck 在 Phys Rev B 26:6104, 1982 中）。这与捕获杂质对位错的固定不同，后者通常在较小的应变幅度下观察到，其特点是弛豫时间短得多，可以有效地解除捕获原子并使位错再次移动。我们研究了冷加工样品的恢复动态，在此期间短片段迅速消失，而最长的片段在较长的退火时间后出现；活化能估计为 22 K——指向热空位辅助过程。晶体缺陷的热横向声子的散射率的补充表征排除了非相互作用移动位错作为主要散射体的可能性。主要结论是，虽然样品的许多特性与孤立滑移位错的 Granato 和 Lücke 理论一致（Granato 和 Lücke in J Appl Phys 27:583, 1956），但低温下的一些观察结果（停止高振幅扭曲后位错的独立固定、零星的雪崩式应变弛豫、声子散射率的平坦温度依赖性）指出存在相互作用的位错，可能排列成位错墙。
We apply two complementary techniques for the characterization of mobile dislocations in samples of hcpwith the concentration of, grown by the blocked capillary method at molar volume 19.5, before and after annealing at temperatures 1.8–2.0 K, and also after work hardening by high-amplitude twisting at 0.03 K and successive recovery at 0.5–1.0 K. The first technique relies on the elastic response of solid helium to oscillatory twisting at frequencies 161 Hz and 931 Hz at temperatures below 1 K, where this response is affected by the presence of mobile dislocations with variable amounts of trappedimpurities. Monitoring the non-equilibrium amplitude dependence after moderate forcing allows to compute the length distributionn(L) of mobile dislocations (Iwasa in J Low Temp Phys 171:30, 2013; Fefferman et al. in Phys Rev B 89:014105, 2014). We also test methods of determiningn(L) from the equilibrium temperature dependence of either real or imaginary part of the shear modulus at small strain amplitudes, based on the values of the damping force measured by Fefferman et al. . The second technique utilizes measurements of thermal conductivity at temperatures below 0.4 K, i.e., of the dislocation-limited mean free path of thermal transverse phonons (Greenberg and Armstrong in Phys Rev B 20:1049, 1979; Armstrong et al. in Phys Rev B 20:1061, 1979). During a prolonged AC-twisting at a high amplitude of strain exceeding the yield stress, long dislocations disappear being replaced by many short ones which remain mobile. However, upon stopping this twisting, the majority of dislocations become immobilized until the sample is warmed up above 0.5 K to speed-up the recovery of dislocations to their mobile state (Day et al. in Phys Rev B 79:214524, 2009; Beamish and Franck in Phys Rev B 26:6104, 1982). This is different from the immobilization of dislocations by trappedimpurities, routinely observed at smaller strain amplitudes, which is characterized by much shorter relaxation times to effectively un-trapatoms and make dislocations mobile again. We investigated the dynamics of the recovery of cold-worked samples, during which short segments quickly disappear, while the longest one appear after longer annealing times; the activation energy was estimated to be 22 K—pointing at the thermal vacancy-assisted process. A complementary characterization by the scattering rate of thermal transverse phonons off crystalline defects rules out non-interacting mobile dislocations as the dominant scatterer. The main conclusion is that while many properties of the sample are consistent with the theory of Granato and Lücke of isolated gliding dislocations (Granato and Lücke in J Appl Phys 27:583, 1956), several observations at low temperatures (-independent immobilization of dislocations after stopping high-amplitude twisting, sporadic avalanche-like relaxation of strain, flat temperature dependence of the phonon scattering rate) point at the presence of interacting dislocations, probably arranged into dislocation walls.
登录
查看更多内容
解释扭转振荡器测量：剪切模量和超固态的影响
影响因子：
2
作者：
J. Reppy;X. Mi;Alexander W. Justin;E. Mueller
通讯作者：
E. Mueller
宇宙学和凝聚态物质中的缺陷演化
DOI：
--
发表时间：
2016
期刊：
影响因子：
--
作者：
C. Martins
通讯作者：
C. Martins
DOI：
--
发表时间：
1976
期刊：
影响因子：
--
作者：
R. Wanner;I. Iwasa;S. Wales
通讯作者：
S. Wales
固体 4He 中的弹性和声学测量
DOI：
--
发表时间：
2012
期刊：
影响因子：
--
作者：
Y. Mukharsky;A. Penzev
通讯作者：
A. Penzev
固体氦中的塑性变形和蠕变
影响因子：
2
作者：
J. Beamish
通讯作者：
J. Beamish