Self-diffusion mechanism in solid sodium by NMR
Self-diffusion mechanism in solid sodium by NMR
复制标题
通过核磁共振研究固体钠的自扩散机制
DOI：
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发表时间：
1980
期刊：
影响因子：
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通讯作者：
D. Wolf
中科院分区：
文献类型：
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作者：
G. Brünger;O. Kanert;D. Wolf
用核磁共振法测定了其在固体钠中的自扩散机理。为此，测量了超纯钠中自旋晶格弛豫时间${T}_{1}$和${T}_{1\ensuremath{\rho} $以及$^ b{23}\ mathm {Na}$的Knight位移$K$作为温度在$10l~Tl~371$ K（熔点）范围内的函数。在所有温度下，Zeeman弛豫时间${T}_{1}$由传导电子决定，导致体积校正的Korringa关系${T}_{1}T=4.68\ifmmode\pm\else\textpm\fi{}0.13$ K s。在150-280 K的温度范围内，观察到由于原子自扩散引起的核偶极相互作用的波动引起的旋转框架弛豫率${T}_{1\ensuremath{\rho}} {\ensuremath{-}1}$。通过将弛豫率的运动诱导部分与Mundy示踪测量值进行比较，确定了相关因子，从而确定了钠中的自扩散机制。假设有以下三种扩散机制可以解释在阿伦尼乌斯图中观察到的曲率：(1)单空位和空空位的结合；(2)单空位与温度相关的指前因子和激活焓；(3)具有空位双跳可能性的单空位。结果表明，测量到的相关因子对温度的依赖性与单位和位差的同时迁移是一致的，而其他两种机制可以被排除为观测到的效应的唯一原因。
The self-diffusion mechanism in solid sodium has been determined by means of NMR. For that purpose, the spin-lattice relaxation times ${T}_{1}$ and ${T}_{1\ensuremath{\rho}}$ and the Knight shift $K$ of $^{23}\mathrm{Na}$ in ultrapure sodium have been measured as a function of temperature in the range of $10l~Tl~371$ K (melting point). At all temperatures, the Zeeman relaxation time ${T}_{1}$ is determined by conduction electrons leading to a volume-corrected Korringa relation of ${T}_{1}T=4.68\ifmmode\pm\else\textpm\fi{}0.13$ K s. In the temperature range 150-280 K, an additional contribution to the rotating-frame relaxation rate, ${T}_{1\ensuremath{\rho}}^{\ensuremath{-}1}$, arising from fluctuations in the nuclear dipole interaction due to atomic self-diffusion is observed. By comparing the motion-induced part of the relaxation rate with the tracer measurements of Mundy, the correlation factor and thus the self-diffusion mechanism in sodium is determined. The following three diffusion mechanisms have been assumed to interpret the observed curvature in the Arrhenius plot: (1) a combination of mono- and divacancies; (2) monovacancies alone with a temperature-dependent pre-exponential factor and activation enthalpy; and (3) monovacancies with the possibility of vacancy double jumps. It is found that the temperature dependence of the measured correlation factor is consistent with the simultaneous migration of mono- and divacancies while the other two mechanisms can be ruled out as solely responsible for the observed effects.