Partition of Solute Atoms among Sublattices in Intermetallic Compounds

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Non-technical Abstract:Many technological materials are compounds with ordered crystal structures. Mechanical strength and other properties have frequently been improved by dissolving solute atoms into the compound. This project will explore how solute atoms partition between sublattices of the host elements. The ways in which solutes partition may have important and unrecognized influences over materials properties. However, the partition, that is, the distribution of solute atoms on the two sublattices, has been difficult to measure. An experimental hyperfine interaction method similar to that used in magnetic resonance imaging will be employed that can measure the distribution accurately. The principal goal is to determine how the precise composition of the host compound, the amount of dissolved solute, and temperature all affect the partition. Knowledge gained should help predict how solutes partition for other combinations of host compounds and solutes and thereby advance the general field of solutions in solids. Other impacts include education and training of undergraduate and graduate students and dissemination of research findings by all research participants to the broader public through participation in scientific meetings, seminars, and publications. Technical Abstract:The goal of this project is to determine how solute atoms partition among different sites in a compound. Considering an ordered binary compound AB2, do solute atoms distribute on one or both sublattices? Investigations will be carried out to determine how the partition varies with deviation from a stoichiometric A:B composition ratio, with the mole fraction of solute, and with temperature. A thematic hypothesis to be explored is that the sum of mole fractions of solutes and antisite atoms is constrained by phase boundaries and the solubility. The partition of solute atoms has heretofore been difficult to measure. Lattice locations of In-probe atoms will be resolved using the nuclear method perturbed angular correlation of gamma rays (PAC). Studies will focus on GdAl2. Phase boundaries and solubility limits will be precisely measured. Solute partition will also be studied in hosts for which the phase field extends to both sides of the stoichiometric composition, leading to differing types of structural point defects. Properties of many functional and structural materials are improved by addition of 1 at.% of solute. The ways in which solutes are partitioned may have important influences over material properties that have not been recognized up until now. The project is expected to comprehensively advance understanding of solute partition. Broader impacts include advanced education and training of students in solid-state physics, nuclear laboratory methods, and data analysis. Research findings are to be disseminated by all research participants to the broader public through participation in local and national scientific meetings, seminars, and publications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.