Solute-solute interactions in intermetallic compounds

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• 作者：Debashis Banerjee ; Ryan Murray ; Gary S. Collins…
• 关键词：Quadrupole interactions ; PAC ; Solute atoms ; Intermetallics ; Defect interactions
• 刊名：Hyperfine Interactions
• 出版年：2017
• 出版时间：November 2017
• 年：2017
• 卷：238
• 期：1
• 全文大小：
• 刊物类别：Physics and Astronomy
• 刊物主题：Nuclear Physics, Heavy Ions, Hadrons; Atomic, Molecular, Optical and Plasma Physics; Condensed Matter Physics; Surfaces and Interfaces, Thin Films;
• 出版者：Springer International Publishing
• ISSN：1572-9540
• 卷排序：238

文摘

Experiments were carried out on highly ordered GdAl₂ samples containing extremely dilute mole fractions of111In/Cd probe-atom solutes (about 10−11), intrinsic antisite atoms Al_Gd having mole fractions of order 0-10−2, and doped with Ag solutes at mole fractions of order 10−2. Three types of defect interactions were investigated. (1) Quadrupole interactions caused by Ag-solute atoms neighboring111In/Cd solute probe atoms were detected using the method of perturbed angular correlation of gamma rays (PAC). Three complexes of pairs of In-probes and Ag-solutes occupying neighboring positions on Gd- and Al-sublattices were identified by comparing site fractions in Gd-poor and Gd-rich GdAl₂(Ag) samples and from the symmetry of the quadrupole interactions. Interaction enthalpies between solute-atom pairs were determined from temperature dependences of observed site fractions. Repulsive interactions were observed for close-neighbor complexes In_Gd+Ag_Gd and In_Gd+Ag_Al pairs, whereas a slightly attractive interaction was observed for In_Al+Ag_Al. Interaction enthalpies were all small, in the range ±0.15 eV. (2) Quadrupole interactions caused by intrinsic antisite atoms Al_Gd neighboring In_Gd probes were also detected and site fractions measured as a function of temperature, as in previous work on samples not doped with Ag-solutes [Temperature- and composition-driven changes in site occupation of solutes in Gd_1+3xAl_2−3x, Zacate and Collins (Phys. Rev. B69, 174202 (1))]. However, the effective binding enthalpy between In_Gd probe and Al_Gd antisite was found to change sign from -0.12 eV (attractive interaction) in undoped samples to + 0.24 eV (repulsive) in Ag-doped samples. This may be attributed to an attractive interaction between Al_Gd antisite atoms and Ag-dopants that competes with the attractive interaction between In_Gd and Al_Gd defects observed in undoped samples. Alternatively, it may be attributed to competing flows of Ag and Al atoms that, in effect, change the numbers of available sites on the two sublattices (termed degeneracies). (3) The site preference of In-probes to occupy Gd- and Al-sublattices, without nearby defects, in Ag-doped samples was measured. Effective transfer enthalpies between the two sublattices were found in doped samples that were much smaller than the value 0.343(3) eV found in the previous study in undoped GdAl₂. Two approaches to understanding why the measured enthalpies in doped and undoped samples differ are discussed.