Study of elementary processes of diffusion in compound crystals of the L1_2 and E2_1 structures by anelastic

几年前，我们提出了在Ni_3Al中观察到的机械弛豫效应是由应力引起的反位Al原子(占据Ni原子位)的扩散跃迁引起的，此后我们通过各种实验来探索这个问题。在本研究的第一年，我们研究了成分偏离化学计量比(25摩尔%Al)对Ni_3Al中弛豫效应的影响。我们发现，松弛速率不依赖于组成，但当组成超过化学计量比时，松弛强度显著增加。这些结果与假设机理的预测很好地吻合。在第二年对Ni3Ga进行了实验，发现了类似的机械松弛效应。弛豫速率及其与温度的关系表明，弛豫是由反位Ga原子引起的。假定Ga在Ni_3Ga中的扩散机制与Al在Ni_3Al中的扩散机制相同，我们计算了Al在Ni_3Al中的扩散系数和Ga在Ni_3Ga中的扩散系数。后者与文献中用放射性示踪实验直接测量的数据接近，表明弛豫实际上是由于反位Ga原子的扩散所致。作为将研究扩展到另一种L1_2化合物Ir_3Nb的准备，我们测量了化学扩散。最后，为了用同样的原理测量氧离子在E2_1(立方钙钛矿)结构的氧化物中的扩散，我们制备了(Ba，Sr)TiO_3样品，我们将在适当的时候对这些样品进行实验。

Several years ago we suggested that the mechanical relaxation effect observed in Ni_3A1 was caused by stress-induced diffusional jumps of anti-site Al atoms (occupying Ni atom sites), and since then we have pursued the problem by carrying out various experiments. In the first year of this investigation we examined the effect of deviation of composition from the stoichiometry (25 mol % Al) on the relaxation effect in Ni_3A1. We found that the relaxation rate did not depend on composition, but the relaxation strength was increased markedly as the composition exceeded the stoichiometry. These results are in excellent agreement with the predictions from the postulated mechanism.Experiments on Ni_3Ga were made in the second year, where a similar mechanical relaxation effect was discovered. The values of the relaxation rate and its temperature dependence indicate that the relaxation is due to anti-site Ga atoms. Assuming that the diffusion of Ga in Ni_3Ga occurs via the same mechanism as the diffusion of Al in Ni_3A1, we have evaluated the diffusion coefficient of Al in Ni_3Al and that of Ga in Ni_3Ga. The latter is close to the data in the literature, which were measured directly by radio-tracer experiments, indicating that the relaxation is in fact due to diffusion of anti-site Ga atoms. As a preparation for extending the study to another L1_2 compound Ir_3Nb, we have measured the chemical diffusion.Lastly, in order to measure the diffusion of oxygen ions in oxides of the E2_1 (cubic perovskite) structure by the same principle, we have prepared samples of (Ba, Sr)TiO_3. We will carry out experiments on these samples in due course.