Site occupation of indium and jump frequencies of cadmium in FeGa3
Site occupation of indium and jump frequencies of cadmium in FeGa3
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FeGa3 中铟的占位和镉的跃迁频率
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
M. Zacate
中科院分区：
文献类型：
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作者：
Randal Newhouse;G. Collins;M. Zacate
使用 In-111 探针对 FeGa3 进行扰动角相关 (PAC) 测量，作为金属间化合物中铟位点占据和镉扩散更广泛研究的一部分。在室温下观察到一个 PAC 信号，其超精细参数 ω1= 513.8(1) Mrad/s 和 η= 0.939(2)。通过与同构 RuIn3 上 PAC 测量中观察到的四极频率进行比较，确定铟仅占据 FeGa3 结构中的 8j 位点（下面表示为 Ga(2)），因为三个 Ga 位点中的两个具有这种点对称性。高温下的 PAC 光谱表现出电场梯度 (EFG) 的阻尼特性，当 Cd 探针在激发的 PAC 能级寿命内在 Ga(2) 位点之间跳跃时，电场梯度会发生波动。开发了一种 EFG 波动的随机模型，该模型基于连接一个 Ga(2) 位点与相邻 Ga(2) 位点的四种可想象的单步跳跃路径，并用于拟合 PAC 光谱。这四种途径导致两种可观察到的 EFG 重新定向率，并且发现这些重新定向率强烈依赖于 EFG 定向。使用密度泛函理论的计算用于减少模型中关于 EFG 方向的未知数。这使得能够以合理的精度确定与位点对称的镜面方向的变化相对应的Ga(2)位点中Cd的总跳跃率。发现该总跳跃率是热激活的，激活焓为 1.8 ±0.1 eV。
Perturbed angular correlation (PAC) measurements using the In-111 probe were carried out on FeGa3 as part of a broader investigation of indium site occupation and cadmium diffusion in intermetallic compounds. One PAC signal was observed with hyperfine parameters ω1= 513.8(1) Mrad/s and η= 0.939(2) at room temperature. By comparison with quadrupole frequencies observed in PAC measurements on isostructural RuIn3, it was determined that indium occupies only the 8j site in the FeGa3 structure, denoted Ga(2) below because two out of the three Ga sites have this point symmetry. PAC spectra at elevated temperature exhibited damping characteristic of electric field gradients (EFGs) that fluctuate as Cd probes jump among Ga(2) sites within the lifetime of the excited PAC level. A stochastic model for the EFG fluctuations based on four conceivable, single-step jump-pathways connecting one Ga(2) site to neighboring Ga(2) sites was developed and used to fit PAC spectra. The four pathways lead to two observable EFG reorientation rates, and these reorientation rates were found to be strongly dependent on EFG orientation. Calculations using density functional theory were used to reduce the number of unknowns in the model with respect to EFG orientation. This made it possible to determine with reasonable precision the total jump rate of Cd among Ga(2) sites that correspond to a change in mirror plane orientation of site-symmetry. This total jump rate was found to be thermally activated with an activation enthalpy of 1.8 ±0.1 eV.