Vacancy encounter model for stochastically fluctuating electric field gradients in the Cu3Au crystal structure
Vacancy encounter model for stochastically fluctuating electric field gradients in the Cu3Au crystal structure
复制标题
Cu3Au 晶体结构中随机波动电场梯度的空位遭遇模型
DOI：
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
J. Williams
中科院分区：
文献类型：
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作者：
M. Zacate;J. Williams
摘要超精细方法是一类通过示踪核的超精细相互作用来测量电场梯度的实验技术。当EFG以与超精细方法的逆特征时间尺度相当的速率波动时，存在可用于确定EFG波动速率的信号相干性的损失。这已被用于测量，例如，EFG波动伴随原子跳跃的放射性示踪剂使用扰动角相关光谱（PAC）。名义上，EFG波动和示踪剂跳跃之间存在一一对应关系，但当示踪剂跳跃由空位扩散机制介导时，多个示踪剂-空位交换的子集在它们发生得比超精细时间尺度快得多时不会影响光谱，如果不考虑这种相关的随机游走效应，则会导致低估潜在的示踪剂跳跃率。目前的工作计算EFG波动率的因素不同的示踪剂跳跃率的基础上的时间依赖性，随机行走分析的示踪剂位移概率在一个空位遇到模型的特殊情况下，在L12晶体结构中的自扩散。
ABSTRACT A class of experimental techniques known as hyperfine methods can be used to measure electric field gradients (EFGs) through the hyperfine interaction experienced by tracer nuclei. When EFGs fluctuate at rates comparable to the inverse characteristic timescale of the hyperfine method, there is a loss of signal coherence that can be used to determine EFG fluctuation rates. This has been used to measure, for example, EFG fluctuations accompanying atomic jumps of radiotracers using perturbed angular correlation spectroscopy (PAC). Nominally, there is a one-to-one correspondence between EFG fluctuation and tracer jump, but when tracer jumps are mediated by a vacancy diffusion mechanism, a subset of multiple tracer-vacancy exchanges will not affect spectra when they occur much faster than the hyperfine timescale, leading to an underestimate of underlying tracer jump rate if this correlated random-walk effect is not taken into consideration. The present work calculates the factor by which EFG fluctuation rate differs from tracer jump rate based on a time-dependent, random-walk analysis of tracer displacement probabilities in a vacancy encounter model for the special case of self-diffusion in the L12 crystal structure.